The secret of science fiction, said H. G. Wells, one of the founders of the genre, is the suspension of disbelief. The writer must introduce something incredible into the real world, but after that, everything flows logically from it. If the whole story is fantastic, it will not be accepted. But if just one item is, then readers are capable of suspending their disbelief.
Unfortunately, I have a harder task than most, because my degrees were in zoology. Most science fiction writers and, for that matter, readers have a general, popular knowledge of physics. They know what is plausible and what isn't. Also, our knowledge of physics is still incomplete, so it is theoretically possible to introduce such concepts as faster-than-light travel or teleportation and they will be accepted, provided they are introduced with a modicum of techno-babble, but not enough to get the reader thinking too deeply.
However, the physics of living flesh are not likely to change radically from one planet or one era to another. Therefore, although we are likely to be amazed at the variety of lifeforms on other planets, once they are discovered, there are some things which are extremely unlikely, if not impossible.
So don't read any further if you don't want your reading of sci-fi to be spoiled.
There are 16 posts, or chapters on this blog. Each one ends with a link to the following one, as well as back to this index. Alternatively, you can click on the "Home" button on the top left hand corner, or the "Older Posts" on the right hand column.
King Kong, Dragons, and the Tyranny of Size. The most common biological mistake of science fiction writers is to ignore the square-cube rule.
Tom Thumb and the Traits of Tininess. What the square-cube rule does to all those stories about shrunken people and tiny humanoids.
Eating for Your Size, or the Secret of the Dinosaurs. Why very big and very small animals have to be constantly eating, and how the dinosaurs got around it.
Geological and Historical Time. The second most common mistake in sci fi. Why the extraterrestrial civilisations most generally depicted will almost certainly not be discovered when we move out into space.
Interplanetary Hybrids. Why they're not possible.
Two Intelligent Species. They can't evolve on the same planet either.
Teeth, Brains, and the Elixir of Youth. These are two things writers usually ignore when describing extreme longevity.
The Trouble with Bionics is that everything is connected to everything else.
No, Mr. Wells, Germs Would Not Stop the Martians because they are adapted solely to terrestrial life.
Four-Armed Bipeds. Artists seem to have great difficulty drawing them. This article explains how it is done.
Evolutionary Anomalies. Evolution can work with only those things it already has - which is why certain combinations are unlikely to occur.
Man-Eating Plants. Why they don't exist, and probably can't exist.
The Trouble With Spock. Even as a boy I could see that a completely logical being such as Spock could not exist.
I now move out of strictly zoological topics to that of cybernetics, in:
Machines Cannot Think or Feel, because the only thing sillier than an intelligent being without emotions is a machine with emotions.
The Future of Robotics does not involve machines in human form.
Finally, I leave zoological issues completely, to remind writers:
Don't Forget the Human Factor. All too often they forget the way human nature works.
Friday 8 August 2014
King Kong, Dragons, and the Tyranny of Size
If there is one biological mistake which science fiction writers make more than any other it is ignoring the consequences of size. Size affects every aspect of an animal's biology, not just its strength. It affects it food requirements, its temperature control, its senses, even its very shape. Yet nearly all of these ramifications are the results of a simple paradox: an animal has three dimensions, but its surfaces and cross-sections have only two.
If, for example, King Kong is five times as tall as a normal gorilla, then it follows he must be five times as wide and five times as deep. Therefore, he must weigh 5 x 5 x 5 = 125 times as much, or about 20 tonnes - three times as much as the tyrannosaur he fought, and probably enough to cave in the roof of the Empire State Building. More relevant would be what it would do to his legs. The cross-section of leg bones would be only 25 times normal because a cross-section, by definition, has width and depth, but no height. It follows that, whenever the huge ape walked, every part of his legs would be carrying five times as much as that of a normal gorilla. The odds are he would break a leg as soon as he stood up.
Even if that were not the case, the acrobatics of the ape in the second King Kong remake would be totally impossible (like just about everything else in that film). When it comes to size, the bigger they are, literally the harder they fall. A mouse can emerged unscathed from a fall which would injure a man, and kill an elephant.
Obviously, King Kong would need a radical reshaping in order to cope. The first thing would be to reduce weight in areas which do not count - such as the non-weightbearing bones. An elephant's skull, for instance, must be huge to house the muscles used in chewing, and to support its tusks, but it is as full of air cavities as a honeycomb.
But the most obvious requirement would be to make his limbs far more massive. Compare a gazelle's legs with those of an elephant's. The limbs of very heavy animals always resemble tree trunks or pillars: very thick, with very broad, flat soles. At the same time, they move in such a fashion as to avoid placing too much weight on any one point for any length of time. Something as small as a gazelle walks on the tips of its toes i.e. its hooves. When it gallops, it launches all four feet off the ground, then lands abruptly on just one. On the other hand, an elephant endeavours, both in walking and running, to keep at least three feet on the ground at any one time.
Admittedly, this is not so easy if one has only two legs, but the bipedal dinosaurs seem to have managed. Nevertheless, their pace would be smoother and more even. Whereas a human being can take all his weight on a single heel, a tyrannosaur, or King Kong, would need to keep much of its weight over the whole foot while the heel of the second touched the ground, then swiftly transfer all the weight to the entire sole in one smooth motion. Even then, there is room for variety. The flesh-eating dinosaurs probably strode pigeon-toed, placing one foot directly in front of the other. A giant ape would be more likely to lurch from side to side.
Viewers of the Jurassic Park franchise may have noticed that the giant dinosaurs seemed to walk in an unnatural fashion: with a slow-motion, rolling sort of gait. Technical limitations may have been partly responsible, but I suspect it was actually a deliberate attempt by the producer to accurately depict the method the giant beasts would have used to transfer their weight. If this sounds cumbersome, remember that the only predator such a giant need fear is one suffering the same size restrictions. Also, animals as big as elephants are capable of surprising bursts of speed - if only because of the length of their stride.
Just the same, even the largest bipedal dinosaur was only a third the weight of King Kong. The fact that nothing so enormous has ever existed should raise doubts about whether one ever could.
Even at more mundane levels, size can have unexpected repercussions. In 1871 two giants got married. Martin Bates was 7 foot 2½ inches [220 cm], his bride, Anna Swan 7 foot 5½ inches [227 cm]. Anna was thus 1.4 times as tall as the average woman, and as the cube of 1.4 is 2.7, you should not be surprised to learn that she weighed 400 lb [182 kg]. Equally, it should be no cause for surprise that her first baby was 27 inches [68½ cm] long and weighted 18 lb [8.2 kg], her second 30 inches [76 cm] and nearly 24 lb [10.9 kg]. The reasons were probably not genetic, but mechanical. Giants typically suffer from excess growth hormone. The grow faster than normal people, but they are not normally born bigger. Anna's children were outsized probably because her womb was large, allowing for more space and more nourishment to grow. However, her birth canal still had only two dimensions to the womb's three. The results was a very protracted labour in both cases, and the death of both babies.
In a race of giants, of course, anatomy would be more closely adjusted to the requirements of reproduction. It would just happen to be different to human anatomy.
Also, although this blog is about zoology rather than botany, a few words need to be said about the absolutely gigantic trees which occasionally turn up in science fiction. If trees were made of stone, they could grow as high as the Washington Monument. If they were made of steel, they could reach the height of the Eiffel Tower. But they are made of wood, whose weight bearing strength is considerably lower. Also, they need to move sap without the use of any active pump. The maximum height on earth is not likely to be greatly excelled on other planets.
So, just what is the maximum size for a flying animal? Everyone knows that the extinct flying reptiles, the pterosaurs were outstanding in this regard: giant flying dinosaurs able to swoop down on any luckless human time traveller and carry him off to their eyries. Well, not exactly. For a variety of reasons, pterosaurs tended to possess longer wings than birds of a comparable body size. Also, the real giants appeared only at the end of the age of reptiles. For the whole of the Jurassic, which lasted 56 million years, only the occasional pterosaur was larger than a chicken.
For a long time the largest pterosaur was thought to be Pteranodon ingens, with a wingspan of 20 feet [6 metres]. Hence, a great deal of study has been done of its probable flying abilities. It is believed to have been a reptilian albatross, soaring on thermals above the sea, and eating fish. Wind tunnel tests suggest that its stalling speed would have been about 10 mph [16 kph], which implies that a headwind greater than that speed would enable it to take off by simply stretching its wings. In lighter breezes it would rise into the air by flapping its wings once a second. After that it would need to flap only on rare occasions. Its low stalling and low sinking speeds allowed it to soar on even the smallest thermals. A difference in temperature between sea and air of a mere one degree would have been sufficient.
All this, however, is somewhat different from how they are portrayed in fiction. For a start, Pteranodon itself weighed no more than a human being, and probably less. In 1971, however, came the discovery of the largest flying animal ever: one of the very last of the pterosaurs, Quetzalcoatlus northropi. Almost everything about the lifestyle of this monster is a matter of controversy, particularly its weight and its flight ability. With a wingspan of 36 feet [11 metres], it had a weight of probably twice that of a human being. It is hard to imagine that such a gigantic creature would be able to fly at all, but its huge wings indicate that it could. It probably stalked over the landscape with its head as high off the ground as a giraffe's, preying on (relatively) smaller reptiles and mammals like some monstrous stork, then flapping its wings to gain altitude before soaring on the hot Cretaceous thermals.
Irrespective of the nature of its aerodynamics, the bottom line is this: the all time monarch of the sky was only twice the size of a man, and at at the maximum size for sustained flight. So where does this leave all those stories of giant birds or reptiles carrying off hapless humans or, on a more positive note, being tamed by man and letting him ride them through the sky? Up in the air, that's where. The only way this could be even marginally possible would be in an environment of very much weaker gravity and/or denser air than we know on earth. Unfortunately, these two conditions tend to be mutually exclusive. If gravity is too weak, a planet is likely to lose its atmosphere. Mars is a good example. Dense atmospheres, on the other hand, will be limited mostly to high gravity planets. There are exceptions, of course, but they come with their own problems. Venus, for instance, is earth sized, but its heavy atmosphere has resulted in a hothouse inimical to life.
As for dragons, you may as well dispense with wings and allow them to fly like Superman. It can be stated with absolute confidence that nothing that size could ever hope to fly except by magic.
Part of the problem should be obvious from the previous discussion. Their spindly legs would collapse under their weight. Their stubby wings would beat uselessly against the weight of their massive bodies. It would be totally impossible to grow to mammalian size without adopting the body proportions of mammals. Nevertheless, one might might ask why a modified version of a giant insect is not possible.
Arthropods, which are what these creepy-crawlies are called, comprise 80% of all animal species in the world, and are by far the most successful of all animal types. Nevertheless, they are all small because they have a number of common features which are only compatible with smallness.
For a start, they have no bones. Their skeletons are completely external. Of course, this is more easily seen in a crustacean such as a lobster or prawn, but anyone who feels, or merely looks at, an insect can see that its "skin" is rigid. This exoskeleton, as it is called, must not only support its weight, but also serve as an attachment for its muscles. Every time it moves its leg, the exoskeleton of that leg will be warped by the pull of the muscles. Again, a ten-fold increase in size would result in a 1000-fold increase in weight and a mere 100-fold increase in the surface of its exoskeleton, leading to a ten-fold increase in the original strain. A 100-fold increase in dimensions means a 100-fold increase in strain. The only solution would be to greatly thicken the integument, then strengthen it with mineral deposits - all adding to its weight and rigidity. The outcome should be obvious. Imagine a knight whose armour must support his body as well as protect him. Imagine a giant tortoise. A spider or praying mantis the size of a lion would be a fearful sight, but you would have no trouble outrunning it.
Although such a cumbersome giant would lose much of its menace, it is nevertheless theoretically possible. But there are other factors. For reasons going back to the evolutionary origin of the group, arthropods do not have a blood circulation system such as ours. Our own bodies are designed so that the internal organs fit into a special body cavity. The corresponding cavity in an arthropod is filled with blood, bathing the innards. A primitive heart is present, along with some major blood vessels, but basically the function of the heart is to keep the blood sloshing around in the body cavity. Such a system works quite well for tiny creatures, but in a large animal it would be totally inefficient. Nevertheless, over vast periods of time evolution could find a solution. It would involve constricting the haemocoele, as the body cavity is called, until it was converted into a complex of genuine blood vessels. However, there is one more, insurmountable problem.
They have no lungs. Instead, respiration is performed by passive diffusion, using tracheae, or fine tubes through the integument, or book lungs, which are actually dry gills, designed to allow diffusion across their folded surface. But diffusion, by its very nature, is a slow process, suitable only for small organisms. Large animals require some sort of pump. And since diffusion is faster at high temperature, it is no mystery why the largest insects and spiders exist in the tropics, and the largest of all occurred in the Carboniferous Era, when the concentration of oxygen in the air was much greater than today.
A giant lobster might be more feasible. At least it had gills, which could probably adapt to large size, and water could support the heavy body.
The reason for these defects, if they can be so called, go back to the very origin of the arthropods. The way in which an animal group can evolve is determined by the direction it took at the very beginning. As an animal becomes larger and more complicated, all it can do is elaborate on the features it already possesses. It may elaborate them to the nth degree, to the point where they are hardly recognizable, but evolving a new organ from scratch is just too difficult. The first fish which crawled ashore were of moderate dimensions, and already possessed an air pocket would could develop into a lung. The first arthropods, however, evolved from very small, segmented worm-like creatures. When they came onto land it was a simple matter to breathe through their skin, then develop pores as the skin hardened. But it meant they could never change. Some creatures are destined to stay small.
It need not, of course, be exactly the same on another planet.
What is not often realised is that the same process applies in evolution. It is simpler for natural selection to alter the basic growth rate, or prolong it for a longer period, than alter the proportions of the parts. For that reason, short races have stumpier legs than tall races. If ever there evolved a race, or even a separate species, of human beings twice as tall as present, we may rest assured that they would be notable for their long, gangling arms and legs - unless, of course, long limbs had for some reason become a disadvantage.
"Unless" is the operative word. For example, the hunting style of cats dictates that their jaws are relatively short. The growth rate of their jaws has been slowed compared to (say) a dog species of the same size. But even then, big cats such as lions have longer jaws than their smaller counterparts.
Often the growth rate changes at certain stages of life e.g. at puberty or at birth. For example, most of the higher animals find it useful to come into the world with a fully functional brain. Thus, brain growth shows positive allometry before birth and negative allometry afterwards. Inevitably, this means that the larger the individual or species, the smaller the brain in relative terms, despite being bigger in absolute terms. The combination of positive allometry for jaws and negative allometry for brains results in an interesting phenomenon: once a certain size is reached there will not be enough space on the skull to anchor the muscles which work the jaws or hold the head upright. In each case, the solution is to produce bony crests along the top, and in a semicircle around the rear, of the skull. Indeed, it is largely the pull of the muscles against the bone during growth which cause the crests to develop, and you can see them on the skulls of any medium to large size mammal. It is only small animals and those, like us, with large brains who possess smooth skulls.
The rule of allometry applies to almost every external feature - tail, combs, crests, tufts of hair or feathers - wherever it is not actually ruled out by more important size restraints, or by special environmental considerations. Perhaps the most visible application is with elongated animals. An anaconda is not simply a common grass snake built large. If it were, it would have difficulty supporting its bulk. Elongated animals always become more elongated and thinner as they grow larger. Marine animals are a particular case in point, because the buoyancy of water often permits sizes not possible on land. If a scientist finds a shark tooth twice as long as the largest known specimen, he may rest assured that the owner was a lot more than twice as long. In fact, a really huge marine creature will have more than a passing resemblance to a sea serpent.
Here is a much more detailed academic discussion.
Now click to move to the next article, Tom Thumb and the Traits of Tininess.
Or go back to the Index.
If, for example, King Kong is five times as tall as a normal gorilla, then it follows he must be five times as wide and five times as deep. Therefore, he must weigh 5 x 5 x 5 = 125 times as much, or about 20 tonnes - three times as much as the tyrannosaur he fought, and probably enough to cave in the roof of the Empire State Building. More relevant would be what it would do to his legs. The cross-section of leg bones would be only 25 times normal because a cross-section, by definition, has width and depth, but no height. It follows that, whenever the huge ape walked, every part of his legs would be carrying five times as much as that of a normal gorilla. The odds are he would break a leg as soon as he stood up.
Even if that were not the case, the acrobatics of the ape in the second King Kong remake would be totally impossible (like just about everything else in that film). When it comes to size, the bigger they are, literally the harder they fall. A mouse can emerged unscathed from a fall which would injure a man, and kill an elephant.
Obviously, King Kong would need a radical reshaping in order to cope. The first thing would be to reduce weight in areas which do not count - such as the non-weightbearing bones. An elephant's skull, for instance, must be huge to house the muscles used in chewing, and to support its tusks, but it is as full of air cavities as a honeycomb.
But the most obvious requirement would be to make his limbs far more massive. Compare a gazelle's legs with those of an elephant's. The limbs of very heavy animals always resemble tree trunks or pillars: very thick, with very broad, flat soles. At the same time, they move in such a fashion as to avoid placing too much weight on any one point for any length of time. Something as small as a gazelle walks on the tips of its toes i.e. its hooves. When it gallops, it launches all four feet off the ground, then lands abruptly on just one. On the other hand, an elephant endeavours, both in walking and running, to keep at least three feet on the ground at any one time.
Admittedly, this is not so easy if one has only two legs, but the bipedal dinosaurs seem to have managed. Nevertheless, their pace would be smoother and more even. Whereas a human being can take all his weight on a single heel, a tyrannosaur, or King Kong, would need to keep much of its weight over the whole foot while the heel of the second touched the ground, then swiftly transfer all the weight to the entire sole in one smooth motion. Even then, there is room for variety. The flesh-eating dinosaurs probably strode pigeon-toed, placing one foot directly in front of the other. A giant ape would be more likely to lurch from side to side.
Viewers of the Jurassic Park franchise may have noticed that the giant dinosaurs seemed to walk in an unnatural fashion: with a slow-motion, rolling sort of gait. Technical limitations may have been partly responsible, but I suspect it was actually a deliberate attempt by the producer to accurately depict the method the giant beasts would have used to transfer their weight. If this sounds cumbersome, remember that the only predator such a giant need fear is one suffering the same size restrictions. Also, animals as big as elephants are capable of surprising bursts of speed - if only because of the length of their stride.
Just the same, even the largest bipedal dinosaur was only a third the weight of King Kong. The fact that nothing so enormous has ever existed should raise doubts about whether one ever could.
Even at more mundane levels, size can have unexpected repercussions. In 1871 two giants got married. Martin Bates was 7 foot 2½ inches [220 cm], his bride, Anna Swan 7 foot 5½ inches [227 cm]. Anna was thus 1.4 times as tall as the average woman, and as the cube of 1.4 is 2.7, you should not be surprised to learn that she weighed 400 lb [182 kg]. Equally, it should be no cause for surprise that her first baby was 27 inches [68½ cm] long and weighted 18 lb [8.2 kg], her second 30 inches [76 cm] and nearly 24 lb [10.9 kg]. The reasons were probably not genetic, but mechanical. Giants typically suffer from excess growth hormone. The grow faster than normal people, but they are not normally born bigger. Anna's children were outsized probably because her womb was large, allowing for more space and more nourishment to grow. However, her birth canal still had only two dimensions to the womb's three. The results was a very protracted labour in both cases, and the death of both babies.
In a race of giants, of course, anatomy would be more closely adjusted to the requirements of reproduction. It would just happen to be different to human anatomy.
Also, although this blog is about zoology rather than botany, a few words need to be said about the absolutely gigantic trees which occasionally turn up in science fiction. If trees were made of stone, they could grow as high as the Washington Monument. If they were made of steel, they could reach the height of the Eiffel Tower. But they are made of wood, whose weight bearing strength is considerably lower. Also, they need to move sap without the use of any active pump. The maximum height on earth is not likely to be greatly excelled on other planets.
Flight
Have you ever wondered why the largest birds, such as the ostrich and emu, are all flightless? Nowhere is the tyranny of size so evident as in flight. A 2-D wingspan is required to lift a 3-D body off the ground, a body whose greatest bulk lies in the very muscles which operate the wings. And the only thing holding up the wings is air, which is not a notoriously heavy medium. Increase in size means a rapid increase in the weight/lift ratio, which soon reaches a critical limit. For this reason, large birds such as swans are cumbersome at take off, getting airborne being rather more difficult than staying aloft. Even the 20 lb [9 kg] albatross is adapted for long-distance soaring rather than flapping flight. Indeed, all large birds operate close to their weight/lift limit; their prey must be much smaller than themselves if they have any hope of flying off with it.So, just what is the maximum size for a flying animal? Everyone knows that the extinct flying reptiles, the pterosaurs were outstanding in this regard: giant flying dinosaurs able to swoop down on any luckless human time traveller and carry him off to their eyries. Well, not exactly. For a variety of reasons, pterosaurs tended to possess longer wings than birds of a comparable body size. Also, the real giants appeared only at the end of the age of reptiles. For the whole of the Jurassic, which lasted 56 million years, only the occasional pterosaur was larger than a chicken.
For a long time the largest pterosaur was thought to be Pteranodon ingens, with a wingspan of 20 feet [6 metres]. Hence, a great deal of study has been done of its probable flying abilities. It is believed to have been a reptilian albatross, soaring on thermals above the sea, and eating fish. Wind tunnel tests suggest that its stalling speed would have been about 10 mph [16 kph], which implies that a headwind greater than that speed would enable it to take off by simply stretching its wings. In lighter breezes it would rise into the air by flapping its wings once a second. After that it would need to flap only on rare occasions. Its low stalling and low sinking speeds allowed it to soar on even the smallest thermals. A difference in temperature between sea and air of a mere one degree would have been sufficient.
All this, however, is somewhat different from how they are portrayed in fiction. For a start, Pteranodon itself weighed no more than a human being, and probably less. In 1971, however, came the discovery of the largest flying animal ever: one of the very last of the pterosaurs, Quetzalcoatlus northropi. Almost everything about the lifestyle of this monster is a matter of controversy, particularly its weight and its flight ability. With a wingspan of 36 feet [11 metres], it had a weight of probably twice that of a human being. It is hard to imagine that such a gigantic creature would be able to fly at all, but its huge wings indicate that it could. It probably stalked over the landscape with its head as high off the ground as a giraffe's, preying on (relatively) smaller reptiles and mammals like some monstrous stork, then flapping its wings to gain altitude before soaring on the hot Cretaceous thermals.
Irrespective of the nature of its aerodynamics, the bottom line is this: the all time monarch of the sky was only twice the size of a man, and at at the maximum size for sustained flight. So where does this leave all those stories of giant birds or reptiles carrying off hapless humans or, on a more positive note, being tamed by man and letting him ride them through the sky? Up in the air, that's where. The only way this could be even marginally possible would be in an environment of very much weaker gravity and/or denser air than we know on earth. Unfortunately, these two conditions tend to be mutually exclusive. If gravity is too weak, a planet is likely to lose its atmosphere. Mars is a good example. Dense atmospheres, on the other hand, will be limited mostly to high gravity planets. There are exceptions, of course, but they come with their own problems. Venus, for instance, is earth sized, but its heavy atmosphere has resulted in a hothouse inimical to life.
As for dragons, you may as well dispense with wings and allow them to fly like Superman. It can be stated with absolute confidence that nothing that size could ever hope to fly except by magic.
Giant Arthropods
Giant insects and spiders (no, spiders are not insects!) have long being a mainstay of science fiction. The tremendous strength and voracity of these tiny monsters, their utter, insensate "otherness" in their normal size, makes the thought of expanding them to our own size frame send a shiver up the average person's spine. Seldom does it occur to anyone to ask why they have never reached such a size on our own world.Part of the problem should be obvious from the previous discussion. Their spindly legs would collapse under their weight. Their stubby wings would beat uselessly against the weight of their massive bodies. It would be totally impossible to grow to mammalian size without adopting the body proportions of mammals. Nevertheless, one might might ask why a modified version of a giant insect is not possible.
Arthropods, which are what these creepy-crawlies are called, comprise 80% of all animal species in the world, and are by far the most successful of all animal types. Nevertheless, they are all small because they have a number of common features which are only compatible with smallness.
For a start, they have no bones. Their skeletons are completely external. Of course, this is more easily seen in a crustacean such as a lobster or prawn, but anyone who feels, or merely looks at, an insect can see that its "skin" is rigid. This exoskeleton, as it is called, must not only support its weight, but also serve as an attachment for its muscles. Every time it moves its leg, the exoskeleton of that leg will be warped by the pull of the muscles. Again, a ten-fold increase in size would result in a 1000-fold increase in weight and a mere 100-fold increase in the surface of its exoskeleton, leading to a ten-fold increase in the original strain. A 100-fold increase in dimensions means a 100-fold increase in strain. The only solution would be to greatly thicken the integument, then strengthen it with mineral deposits - all adding to its weight and rigidity. The outcome should be obvious. Imagine a knight whose armour must support his body as well as protect him. Imagine a giant tortoise. A spider or praying mantis the size of a lion would be a fearful sight, but you would have no trouble outrunning it.
Although such a cumbersome giant would lose much of its menace, it is nevertheless theoretically possible. But there are other factors. For reasons going back to the evolutionary origin of the group, arthropods do not have a blood circulation system such as ours. Our own bodies are designed so that the internal organs fit into a special body cavity. The corresponding cavity in an arthropod is filled with blood, bathing the innards. A primitive heart is present, along with some major blood vessels, but basically the function of the heart is to keep the blood sloshing around in the body cavity. Such a system works quite well for tiny creatures, but in a large animal it would be totally inefficient. Nevertheless, over vast periods of time evolution could find a solution. It would involve constricting the haemocoele, as the body cavity is called, until it was converted into a complex of genuine blood vessels. However, there is one more, insurmountable problem.
They have no lungs. Instead, respiration is performed by passive diffusion, using tracheae, or fine tubes through the integument, or book lungs, which are actually dry gills, designed to allow diffusion across their folded surface. But diffusion, by its very nature, is a slow process, suitable only for small organisms. Large animals require some sort of pump. And since diffusion is faster at high temperature, it is no mystery why the largest insects and spiders exist in the tropics, and the largest of all occurred in the Carboniferous Era, when the concentration of oxygen in the air was much greater than today.
A giant lobster might be more feasible. At least it had gills, which could probably adapt to large size, and water could support the heavy body.
The reason for these defects, if they can be so called, go back to the very origin of the arthropods. The way in which an animal group can evolve is determined by the direction it took at the very beginning. As an animal becomes larger and more complicated, all it can do is elaborate on the features it already possesses. It may elaborate them to the nth degree, to the point where they are hardly recognizable, but evolving a new organ from scratch is just too difficult. The first fish which crawled ashore were of moderate dimensions, and already possessed an air pocket would could develop into a lung. The first arthropods, however, evolved from very small, segmented worm-like creatures. When they came onto land it was a simple matter to breathe through their skin, then develop pores as the skin hardened. But it meant they could never change. Some creatures are destined to stay small.
It need not, of course, be exactly the same on another planet.
Allometry, or Why One Part is Longer Than Another
In everyday life we take it for granted that the proportions of the body change with growth. A baby comes into the world with short, stubby limbs. In order to reach adult proportions, they have to grow faster than the body as a whole - a phenomenon known as positive allometry. A side effect of that this process is that a tall person's limbs are also longer in proportion to his body than those of a short person. "Long and lanky" is a phrase that rolls off the tongue as readily as "short and stocky". Not everyone fits these stereotypes, of course. People grow sideways as well as upwards, so one can be tall and solid, or short and slight, but never, never tall and stocky.What is not often realised is that the same process applies in evolution. It is simpler for natural selection to alter the basic growth rate, or prolong it for a longer period, than alter the proportions of the parts. For that reason, short races have stumpier legs than tall races. If ever there evolved a race, or even a separate species, of human beings twice as tall as present, we may rest assured that they would be notable for their long, gangling arms and legs - unless, of course, long limbs had for some reason become a disadvantage.
"Unless" is the operative word. For example, the hunting style of cats dictates that their jaws are relatively short. The growth rate of their jaws has been slowed compared to (say) a dog species of the same size. But even then, big cats such as lions have longer jaws than their smaller counterparts.
Often the growth rate changes at certain stages of life e.g. at puberty or at birth. For example, most of the higher animals find it useful to come into the world with a fully functional brain. Thus, brain growth shows positive allometry before birth and negative allometry afterwards. Inevitably, this means that the larger the individual or species, the smaller the brain in relative terms, despite being bigger in absolute terms. The combination of positive allometry for jaws and negative allometry for brains results in an interesting phenomenon: once a certain size is reached there will not be enough space on the skull to anchor the muscles which work the jaws or hold the head upright. In each case, the solution is to produce bony crests along the top, and in a semicircle around the rear, of the skull. Indeed, it is largely the pull of the muscles against the bone during growth which cause the crests to develop, and you can see them on the skulls of any medium to large size mammal. It is only small animals and those, like us, with large brains who possess smooth skulls.
The rule of allometry applies to almost every external feature - tail, combs, crests, tufts of hair or feathers - wherever it is not actually ruled out by more important size restraints, or by special environmental considerations. Perhaps the most visible application is with elongated animals. An anaconda is not simply a common grass snake built large. If it were, it would have difficulty supporting its bulk. Elongated animals always become more elongated and thinner as they grow larger. Marine animals are a particular case in point, because the buoyancy of water often permits sizes not possible on land. If a scientist finds a shark tooth twice as long as the largest known specimen, he may rest assured that the owner was a lot more than twice as long. In fact, a really huge marine creature will have more than a passing resemblance to a sea serpent.
Here is a much more detailed academic discussion.
Now click to move to the next article, Tom Thumb and the Traits of Tininess.
Or go back to the Index.
Thursday 7 August 2014
Tom Thumb and the Traits of Tininess
Tom Thumb is one of the more enduring children's stories, while in adult literature one of the more enduring images is of Gulliver pinned down by the strings of the tiny Lilliputians. Meanwhile, the number of science fiction stories featuring shrunken humans or tiny humanoids is legion. Therefore, let us see how this concept stacks up against biology.
From what you have just read, you might think that large size is a hindrance rather than a help. Nevertheless, let's not forget that the dinosaurs lasted 120 million years, and if it hadn't been for the asteroid, they would probably still be here today. The fact is, within a species, the larger individuals tend to be dominant, have preferential access to resources, and are better at dealing with predators and prey. Thus, the species itself will tend to grow bigger with time - a phenomenon known as Cope's rule. Each species will therefore end up the maximum size possible for its lifestyle and habitat. Just the same, most of the giants are now extinct. Huge animals are evolutionary dead ends. They are too specialised, they need too much space and too much food, and they breed too slowly to respond to changing conditions. Also, even during the age of giants, the vast majority of species were small.
Their first trait of the tiny is their enormous relative strength. A man with the strength of an ant could lift a house. A flea the size of a man could leap tall buildings in a single bound. This sort of thing is grist to the mill of popular science articles, and there is a tendency among the less informed sci fi writers to take it literally. Again, you may pause to wonder why no animals of such tremendous strength have ever been known. The reason, of course, is the same square-cube rule which allows them to walk on spindly legs: their skeletons and muscles have a much greater cross-section per unit weight.
Likewise, although gorillas only occasionally climb trees, a mouse can scurry up a vertical trunk because its claws can find a grip on the tiniest crevices in the bark, and both claws and bark are firm enough to hold its tiny weight. Shrunken even further, an animal has the option of furnishing its extremities with tiny suction caps or drops of glue. In the 1986 version of The Fly, we saw a scientist genetically amalgamated with a fly (another biological impossibility) walk upside down on the ceiling. Nowhere was there any indication of how he could have done so. It was apparently some occult power granted only to flies, and unrelated to anything biological.
Another major characteristic of small animals, and a major handicap at that, is that they have a much greater surface area to body mass. This means that they gain and lose heat very quickly. This will be explored fully in the next chapter. In the meantime -
Insects, of course, do not possess voices as such. Their calls are made by rubbing, tapping, or vibrating their extremities. True voices are the possession of land vertebrates with lungs able to pass air over such organs as vocal chords, and allow it to resonate in their mouths and noses. The resultant sound vibrates at the natural frequency of the vocal structures, and thus the pitch is inversely proportional to their size. Thus, small animals produce high-pitched squeaks, squeals, and chirps, while larger species growl, roar, or bellow at a lower frequency.
There is an unexpected side effect to all of this. High-pitched sounds are the least dampened when they bounce off objects i.e. they produce the best echoes. They are therefore ideal for echolocation. When something is small as a shrew scurries around, the tiny squeaks it utters to keep in contact with other shrews may also act as a form of radar in the dark. It is not well known that some species of shrew can echolocate, just like bats.
This does not mean, of course, that larger species cannot echolocate; just look at dolphins. However, it does mean that it would have to fit into the general evolutionary scheme of things. An organ cannot evolve unless there is a continuing function for it all the way along the line. Therefore, if human beings could echolocate, you may take it for granted that apes and monkeys could do so too. It would have evolved when our ancestors were shrew sized, and would have required a gradual restructuring of the vocal apparatus as size increased - provided there was a continuing need for echolocation all through the evolutionary process.
At the other end of the scale, it has only recently been discovered that elephants communicate by infra-sound: deep rumbles too low in frequency for the human ear to hear, but which are nevertheless very loud. Sections of the herd can keep in touch while being separated by several miles, and a cow on heat will drive bulls mad for miles around. The implications are staggering, and are only now being worked out. One wonders what it was like with the dinosaurs. The corollary of all this is that a species' hearing ability is dependent on size, for hearing is simply registering the beating of waves of air pressure against the ear drum, whose size is dependent on the overall size of the animal. Thus, every species is more sensitive to the same frequencies of sound it makes.
However, not everything in the animal kingdom is relative. For some items, bigger really is better, and those items are eyes and brains. An eye is essentially a globular camera, focusing light on the light-sensitive cells at the rear. The optical acuity ie how much fine detail can be distinguished, is determined by the absolute number of these cells, and there is a limit as to how closely they can be packed. So, for example, although a whale's eye appears small in comparison to its body, in absolute terms it is a very big eye, capable of high resolution. A mouse's eye, on the other hand, is big in proportion to its body - indeed, it bulges - but is small in absolute terms. Not only that, but because the retina, or rear of the eye, is so close to the lens, there is the added difficulty of focusing the light on the retina. The lens must swell, thus occupying more relative space in the eyeball, and putting it even closer to the retina. It is a vicious circle, and there is nothing the poor creature can do about it except to put its trust in its nose and ears.
Most of you are probably aware that insects possess compound eyes radically different from our own. Indeed, it is common in the movies to show them receiving a hundred different versions of the same scene. This is a gross misconception. Essentially, each unit of the eye, or ommatidium, is a miniature eye, with its own lens and retina, allowing a single unit of light to be recorded by the brain. This is very much less efficient than a similarly sized vertebrate eye, and visual acuity is far too low to permit accurate recognition of form. How often have you said, "I'd like to be a fly on the wall when such-and-such happens"? You wouldn't see much.
A similar situation occurs with brains, but the pattern is more complex. In the simplest terms, we may distinguish between the functional part of the brain, which controls respiration, digestion, the senses, and movement, and the intelligence part, which overlays the former. An elephant's brain is three times as big as ours, because it needs a larger functional brain. But there is not a one-to-one ratio because, after all, a brain can tell a big muscle to contract just as easily as a small one. A man is smarter than a chimpanzee because the intelligence section of his brain is bigger. Nevertheless, among humans, IQ has very little to do with brain size, and a lot more to do with the complexity of the interconnections within the brain.
But the bottom line is, within broad limits, intelligence is dependent on brain size. It is just not possible to fit a human-like intelligence into the skull of a monkey. And Gulliver's Lilliputians would not only have very poor eyesight; they would not be able to think in any real fashion.
It is also germane to mention that large brains have one major disadvantage: getting into the world. In most species the newborn brain is about 90% of the adult size. With human babies it is 26%. Just the same, their large skulls are the reason women have such difficult births, and this is going to be a major problem in the evolution of the human brain.
Let us now visualise an alien half the dimensions of a human being. Its weight would be only an eighth of ours, but its brain, and probably its eyes, would be comparable in size to our own. In other words, it would possess eyes and a globular cranium out of all proportion to its diminutive stature, or even to its small jaws and nose. If you follow the UFO scene, you will know exactly what I mean. This is a perfect description of the "greys": the most common humanoid seen in relation to flying saucers. Like science fiction writers, very few ufologists knew much about biology, so hardly any have commented on the fact that the greys so closely satisfy predictions made on purely biological grounds. This fact might suggest that they are not mere figments of the imagination. (How they manage to reproduce is, however, an unsolved issue.)
Now, you may wish to go to the next chapter, Eating for Your Size, or the Secret of the Dinosaurs.
Or go back to the Index.
From what you have just read, you might think that large size is a hindrance rather than a help. Nevertheless, let's not forget that the dinosaurs lasted 120 million years, and if it hadn't been for the asteroid, they would probably still be here today. The fact is, within a species, the larger individuals tend to be dominant, have preferential access to resources, and are better at dealing with predators and prey. Thus, the species itself will tend to grow bigger with time - a phenomenon known as Cope's rule. Each species will therefore end up the maximum size possible for its lifestyle and habitat. Just the same, most of the giants are now extinct. Huge animals are evolutionary dead ends. They are too specialised, they need too much space and too much food, and they breed too slowly to respond to changing conditions. Also, even during the age of giants, the vast majority of species were small.
Their first trait of the tiny is their enormous relative strength. A man with the strength of an ant could lift a house. A flea the size of a man could leap tall buildings in a single bound. This sort of thing is grist to the mill of popular science articles, and there is a tendency among the less informed sci fi writers to take it literally. Again, you may pause to wonder why no animals of such tremendous strength have ever been known. The reason, of course, is the same square-cube rule which allows them to walk on spindly legs: their skeletons and muscles have a much greater cross-section per unit weight.
Likewise, although gorillas only occasionally climb trees, a mouse can scurry up a vertical trunk because its claws can find a grip on the tiniest crevices in the bark, and both claws and bark are firm enough to hold its tiny weight. Shrunken even further, an animal has the option of furnishing its extremities with tiny suction caps or drops of glue. In the 1986 version of The Fly, we saw a scientist genetically amalgamated with a fly (another biological impossibility) walk upside down on the ceiling. Nowhere was there any indication of how he could have done so. It was apparently some occult power granted only to flies, and unrelated to anything biological.
Another major characteristic of small animals, and a major handicap at that, is that they have a much greater surface area to body mass. This means that they gain and lose heat very quickly. This will be explored fully in the next chapter. In the meantime -
Sound
The sounds made by the very small are high-pitched as well as soft. Sound is caused by movement of air, and its frequency, naturally enough, by the frequency at which the sound maker vibrates. An eagle simply cannot flap its wings 1,000 times a second, neither would it need to. On the other hand, a humming bird, with much smaller wings, and the need to hover on one spot, beats its wings into a humming blur. At the bottom of the scale, a mosquito's wings beat so fast they produce a high-pitched whine.Insects, of course, do not possess voices as such. Their calls are made by rubbing, tapping, or vibrating their extremities. True voices are the possession of land vertebrates with lungs able to pass air over such organs as vocal chords, and allow it to resonate in their mouths and noses. The resultant sound vibrates at the natural frequency of the vocal structures, and thus the pitch is inversely proportional to their size. Thus, small animals produce high-pitched squeaks, squeals, and chirps, while larger species growl, roar, or bellow at a lower frequency.
There is an unexpected side effect to all of this. High-pitched sounds are the least dampened when they bounce off objects i.e. they produce the best echoes. They are therefore ideal for echolocation. When something is small as a shrew scurries around, the tiny squeaks it utters to keep in contact with other shrews may also act as a form of radar in the dark. It is not well known that some species of shrew can echolocate, just like bats.
This does not mean, of course, that larger species cannot echolocate; just look at dolphins. However, it does mean that it would have to fit into the general evolutionary scheme of things. An organ cannot evolve unless there is a continuing function for it all the way along the line. Therefore, if human beings could echolocate, you may take it for granted that apes and monkeys could do so too. It would have evolved when our ancestors were shrew sized, and would have required a gradual restructuring of the vocal apparatus as size increased - provided there was a continuing need for echolocation all through the evolutionary process.
At the other end of the scale, it has only recently been discovered that elephants communicate by infra-sound: deep rumbles too low in frequency for the human ear to hear, but which are nevertheless very loud. Sections of the herd can keep in touch while being separated by several miles, and a cow on heat will drive bulls mad for miles around. The implications are staggering, and are only now being worked out. One wonders what it was like with the dinosaurs. The corollary of all this is that a species' hearing ability is dependent on size, for hearing is simply registering the beating of waves of air pressure against the ear drum, whose size is dependent on the overall size of the animal. Thus, every species is more sensitive to the same frequencies of sound it makes.
Of Eyes and Brains
Another characteristic of small animals is that their internal set-up is simpler. The inhabitants of Lilliput, being one sixth the dimensions of normal people, would not only lose and gain heat much more quickly, but they would lack the highly complex system of small blood vessels we require, since every part of their bodies would be in close proximity to a source of blood. If humans were to be artificially shrunk, then they would not only lose cells, but their internal complexity would have to collapse.However, not everything in the animal kingdom is relative. For some items, bigger really is better, and those items are eyes and brains. An eye is essentially a globular camera, focusing light on the light-sensitive cells at the rear. The optical acuity ie how much fine detail can be distinguished, is determined by the absolute number of these cells, and there is a limit as to how closely they can be packed. So, for example, although a whale's eye appears small in comparison to its body, in absolute terms it is a very big eye, capable of high resolution. A mouse's eye, on the other hand, is big in proportion to its body - indeed, it bulges - but is small in absolute terms. Not only that, but because the retina, or rear of the eye, is so close to the lens, there is the added difficulty of focusing the light on the retina. The lens must swell, thus occupying more relative space in the eyeball, and putting it even closer to the retina. It is a vicious circle, and there is nothing the poor creature can do about it except to put its trust in its nose and ears.
Most of you are probably aware that insects possess compound eyes radically different from our own. Indeed, it is common in the movies to show them receiving a hundred different versions of the same scene. This is a gross misconception. Essentially, each unit of the eye, or ommatidium, is a miniature eye, with its own lens and retina, allowing a single unit of light to be recorded by the brain. This is very much less efficient than a similarly sized vertebrate eye, and visual acuity is far too low to permit accurate recognition of form. How often have you said, "I'd like to be a fly on the wall when such-and-such happens"? You wouldn't see much.
A similar situation occurs with brains, but the pattern is more complex. In the simplest terms, we may distinguish between the functional part of the brain, which controls respiration, digestion, the senses, and movement, and the intelligence part, which overlays the former. An elephant's brain is three times as big as ours, because it needs a larger functional brain. But there is not a one-to-one ratio because, after all, a brain can tell a big muscle to contract just as easily as a small one. A man is smarter than a chimpanzee because the intelligence section of his brain is bigger. Nevertheless, among humans, IQ has very little to do with brain size, and a lot more to do with the complexity of the interconnections within the brain.
But the bottom line is, within broad limits, intelligence is dependent on brain size. It is just not possible to fit a human-like intelligence into the skull of a monkey. And Gulliver's Lilliputians would not only have very poor eyesight; they would not be able to think in any real fashion.
It is also germane to mention that large brains have one major disadvantage: getting into the world. In most species the newborn brain is about 90% of the adult size. With human babies it is 26%. Just the same, their large skulls are the reason women have such difficult births, and this is going to be a major problem in the evolution of the human brain.
Let us now visualise an alien half the dimensions of a human being. Its weight would be only an eighth of ours, but its brain, and probably its eyes, would be comparable in size to our own. In other words, it would possess eyes and a globular cranium out of all proportion to its diminutive stature, or even to its small jaws and nose. If you follow the UFO scene, you will know exactly what I mean. This is a perfect description of the "greys": the most common humanoid seen in relation to flying saucers. Like science fiction writers, very few ufologists knew much about biology, so hardly any have commented on the fact that the greys so closely satisfy predictions made on purely biological grounds. This fact might suggest that they are not mere figments of the imagination. (How they manage to reproduce is, however, an unsolved issue.)
Now, you may wish to go to the next chapter, Eating for Your Size, or the Secret of the Dinosaurs.
Or go back to the Index.
Eating for Your Size, or the Secret of the Dinosaurs
Shrews and sauropods will both be germane to this discussion, but I shall frame it by asking: how did the dinosaurs get so big, and why has nothing else ever grown so huge?
Well, first of all, is the second half of that question correct? Yes and no. The sauropods were certainly the most gigantic animals ever to walk the earth. These were the familiar four-poster, hump-backed dinosaurs with ridiculously small heads and incredibly long necks and tails. And they were BIG - an order of magnitude bigger than any other dinosaur. Even the smallest topped the ton, and the largest, Argentinosaurus may have reached 90 tonnes. Few of the other dinosaurs, including those two-legged terrors we've all come to love, would have gone beyond 8½ tonnes, the weight of a very heavy elephant, and some were as small as chickens.
To put this in perspective, a big giraffe will weigh about a tonne and stand 5.5 metres [18 feet] high. Now imagine a hornless rhinoceros standing that high at the shoulder, with a neck stretching out to allow it to browse 8 metres [26 feet] above the ground. That was Paraceratherium, which shook the ground of Asia until 23 million years ago. The very biggest specimens may have reached 12 metres [39 feet] in length and weighed in at up to 20 tonnes: far bigger than any non-sauropod dinosaur. It was the largest land mammal which has ever existed, probably the largest which could ever exist.
Nevertheless, one has to admit that, when considering the total mass of flesh on the ground at any one time, the age of dinosaurs comes up trumps. Why?
Well, for a start, there were marginally fewer changes in climate over that period than during the age of mammals, so giants could continue to grow before they were cut down by changed circumstances. Also, the Mesozoic was generally hotter than it is now. However, the major reason can be expressed in four points.
- Every animal needs to eat. Some of the food goes to energy, some to maintenance, some to growth (when young), and some to wastage, because it cannot be digested.
- Big animals require more food in absolute terms.
- Small animals require more food in relative terms.
- Warm-blooded animals require more food than cold-blooded ones.
The first point should be so blatantly obvious it need not be mentioned, but it is amazing how often it is overlooked. In the first Alien movie we saw the little monster burst out of its victim's chest and go scurrying into the bowels of the spaceship. When we next saw it, an undisclosed time later, it was big enough to tear a human being limb from limb. What, for heaven's sake, had it been eating all that time? Was it living on stale air?
The second point is also pretty obvious. To grow big requires time, and giant animals always have long gestation periods, and take many years to reach maturity. Many of the smaller rodents, on the other hand, can reproduce when only a few months or a few weeks old, meaning that in good years they can spread out across the land until their populations finally collapse due to starvation: the famous plaques of lemmings, voles, or mice. One never hears of plagues of elephants or rhinoceroses.
However, larger animals do have one advantage: their bodies are more compact. Due to the square cube rule, an ounce of man requires more skin to wrap around it then an ounce of elephant, and an ounce of mouse even more. Of course, it also means a large animal's lungs and bowels must be more convoluted in order to provide more surface for the absorption of air and food respectively.
Nevertheless, it is through the skin that heat and water are lost and gained, putting the small animals at a sizable disadvantage. Even in our own species, a child is more likely to suffer from heat stress, dehydration or hypothermia than its parent. Furthermore, an Eskimo, who needs to conserve heat, is short and squat, with only two thirds of the skin surface of the tally, lanky, but equally heavy natives of northern Australia and the headquarters of the Nile. All other things being equal, species and races are bigger and rounder in cold climates, while in the tropics legs, tails, and ears grow long and spindly.
At the bottom of the size scale the issues are brutal: no matter how well insulated you are, you are going to lose heat and water. The only solution is to replace it - and that means eating and drinking on a magnificent scale. Popular science articles will tell you that if a human being ate as much as a spider he would consume a sheep for breakfast and an ox for both lunch and dinner. I can always remember my lecturer telling us about a small shrew which had to eat a meal every fifteen minutes. "How does it manage to sleep?" I asked. "Very fitfully," he replied. (In practice, it would go into torpor ie drop its temperature to almost the same level as the environment. At night it would close up shop, so to speak. Every sleep would become a mini hibernation.)
Shrews and spiders eat meat, a high quality diet. Vegetation has less nutritional value, so a really tiny herbivore is in a bind. Anyone who has watched a caterpillar on a leaf will know that it is simply an elongated eating machine. A herbivore as small as a dik-dik - a miniature antelope weighing in at 3 - 6 kg [7-16 lb] - tends to seek high quality forage.
An elephant may weigh 1,000 times as much as a dik-dik, but its food requirements are only 180 times as great. Nevertheless, a factor of 180 is not to be sneezed at. So most of the megaherbivores - those weighing more than a tonne - feed on enormous quantities of poor quality, woody material whose digestibility is very low but whose availability is excellent. Thus we have the irony that very large animals spend almost the whole day feeding - just like the very small. They also live a much more sedate lifestyle, not only because they have few enemies, but because they must conserve energy. A giant can put on short bursts of energy - witness a charging elephant - but by and large they move quietly and unhurriedly. It is medium sized animals, such as ourselves, which have time for leisure.
Another strategy of giants in to feed lower down the food chain. The really huge animals are herbivores rather than carnivores. In the sea, where the food chain is much longer, the largest whales and the largest sharks feed on plankton rather than fish.
No contrast could be greater than that between the dignified plodding of an elephant, the friskiness of a gazelle, and the nervous scampering of a mouse. The even tinier shrew is an even greater bundle of frenzied energy, forever hurrying down its well worn pathways in the grass, constantly squeaking its ultrasonic contact calls, forever on the alert for prey or predators, as if its life depended on being in perpetual motion - as indeed it does. Small animals exist on a higher, faster plane than the rest of us, more active, more ravenous, and more dangerous. Their fires burn more fiercely and burn out more quickly. A year or two is all they can expect to last.
You can see now why a tiny shrew needs to have a meal every fifteen minutes, and why it has to shut down its fires while asleep. Very big mammals face a quite different problem, especially in the tropics: how to lose heat. That is why elephants are hairless, and have big ears. Combined with the need to be constantly eating, that puts a maximum limit to the size of any mammal.
Just the same, from the point of view of an exotherm, massive bulk is a form of insulation. It takes a long time for heat to leak out from the body core, but by the same token, a long time is required to heat up. A crocodile has to sunbathe for several hours in order to reach a workable temperature, and it has been calculated that there are not enough hours in the day for a dinosaur to be able to do it. So how did they manage?
For the past forty years it has been evident that dinosaurs were "warm-blooded", at least to some extent. No doubt it varied with the species and the period. But the most likely scenario is that they had an intermediate metabolism ie they were "luke-warm-blooded". Essentially, they were probably active at a slightly lower body temperature than ours, and achieved it by means of a combination of physiology, and the the insulating effects of size. The fact that their era was normally hotter than ours no doubt helped, although there were dinosaurs thriving during the long nights of the Arctic and Antarctic.
An intermediate metabolism would require a lot less food than a mammal of comparable size, although more than an ordinary reptile. The great sauropods would have munched their way through the Mesozoic like herds of elephants. Dinosaurs the size of elephants, such as Triceratops, would have eaten like a bison. A big carnivore, such as Tyrannosaurus, would have needed as much meat as a lion. A dead Triceratops would have lasted one for months, or until it went putrid. It is more likely they hunted in packs and shared it.
Of course, once the asteroid struck, they all became extinct. The world was inherited by the mammals, which cannot grow any larger than Paraceratherium, and even it was an outlier. The really gigantic monsters will never be seen again.
Here's another look at the issue.
The next chapter is Geological and Historical Time.
Or click to return to the Index.
The second point is also pretty obvious. To grow big requires time, and giant animals always have long gestation periods, and take many years to reach maturity. Many of the smaller rodents, on the other hand, can reproduce when only a few months or a few weeks old, meaning that in good years they can spread out across the land until their populations finally collapse due to starvation: the famous plaques of lemmings, voles, or mice. One never hears of plagues of elephants or rhinoceroses.
However, larger animals do have one advantage: their bodies are more compact. Due to the square cube rule, an ounce of man requires more skin to wrap around it then an ounce of elephant, and an ounce of mouse even more. Of course, it also means a large animal's lungs and bowels must be more convoluted in order to provide more surface for the absorption of air and food respectively.
Nevertheless, it is through the skin that heat and water are lost and gained, putting the small animals at a sizable disadvantage. Even in our own species, a child is more likely to suffer from heat stress, dehydration or hypothermia than its parent. Furthermore, an Eskimo, who needs to conserve heat, is short and squat, with only two thirds of the skin surface of the tally, lanky, but equally heavy natives of northern Australia and the headquarters of the Nile. All other things being equal, species and races are bigger and rounder in cold climates, while in the tropics legs, tails, and ears grow long and spindly.
At the bottom of the size scale the issues are brutal: no matter how well insulated you are, you are going to lose heat and water. The only solution is to replace it - and that means eating and drinking on a magnificent scale. Popular science articles will tell you that if a human being ate as much as a spider he would consume a sheep for breakfast and an ox for both lunch and dinner. I can always remember my lecturer telling us about a small shrew which had to eat a meal every fifteen minutes. "How does it manage to sleep?" I asked. "Very fitfully," he replied. (In practice, it would go into torpor ie drop its temperature to almost the same level as the environment. At night it would close up shop, so to speak. Every sleep would become a mini hibernation.)
Shrews and spiders eat meat, a high quality diet. Vegetation has less nutritional value, so a really tiny herbivore is in a bind. Anyone who has watched a caterpillar on a leaf will know that it is simply an elongated eating machine. A herbivore as small as a dik-dik - a miniature antelope weighing in at 3 - 6 kg [7-16 lb] - tends to seek high quality forage.
An elephant may weigh 1,000 times as much as a dik-dik, but its food requirements are only 180 times as great. Nevertheless, a factor of 180 is not to be sneezed at. So most of the megaherbivores - those weighing more than a tonne - feed on enormous quantities of poor quality, woody material whose digestibility is very low but whose availability is excellent. Thus we have the irony that very large animals spend almost the whole day feeding - just like the very small. They also live a much more sedate lifestyle, not only because they have few enemies, but because they must conserve energy. A giant can put on short bursts of energy - witness a charging elephant - but by and large they move quietly and unhurriedly. It is medium sized animals, such as ourselves, which have time for leisure.
Another strategy of giants in to feed lower down the food chain. The really huge animals are herbivores rather than carnivores. In the sea, where the food chain is much longer, the largest whales and the largest sharks feed on plankton rather than fish.
No contrast could be greater than that between the dignified plodding of an elephant, the friskiness of a gazelle, and the nervous scampering of a mouse. The even tinier shrew is an even greater bundle of frenzied energy, forever hurrying down its well worn pathways in the grass, constantly squeaking its ultrasonic contact calls, forever on the alert for prey or predators, as if its life depended on being in perpetual motion - as indeed it does. Small animals exist on a higher, faster plane than the rest of us, more active, more ravenous, and more dangerous. Their fires burn more fiercely and burn out more quickly. A year or two is all they can expect to last.
Warm-bloodedness
Now we come to the last point. Warm- and cold-bloodedness are really misleading terms, because both groups function at similar temperatures. The difference is that one group has to bask in the sun to reach the appropriate temperature, while the other relies on a complex system of circulation, digestion, and locomotion in order to raise their internal temperature, plus insulation in the form of fur or feathers to keep it in. The official terms are "ectothermy" (external heat) and "endothermy" (internal heat). Because we ourselves are endotherms, we assume that endotherms are superior, and in general terms, they are. However, they suffer one major drawback: they requires much more food in order to stoke their internal fires. An endotherm needs five to ten times as much food as an exotherm of the same weight.You can see now why a tiny shrew needs to have a meal every fifteen minutes, and why it has to shut down its fires while asleep. Very big mammals face a quite different problem, especially in the tropics: how to lose heat. That is why elephants are hairless, and have big ears. Combined with the need to be constantly eating, that puts a maximum limit to the size of any mammal.
Just the same, from the point of view of an exotherm, massive bulk is a form of insulation. It takes a long time for heat to leak out from the body core, but by the same token, a long time is required to heat up. A crocodile has to sunbathe for several hours in order to reach a workable temperature, and it has been calculated that there are not enough hours in the day for a dinosaur to be able to do it. So how did they manage?
For the past forty years it has been evident that dinosaurs were "warm-blooded", at least to some extent. No doubt it varied with the species and the period. But the most likely scenario is that they had an intermediate metabolism ie they were "luke-warm-blooded". Essentially, they were probably active at a slightly lower body temperature than ours, and achieved it by means of a combination of physiology, and the the insulating effects of size. The fact that their era was normally hotter than ours no doubt helped, although there were dinosaurs thriving during the long nights of the Arctic and Antarctic.
An intermediate metabolism would require a lot less food than a mammal of comparable size, although more than an ordinary reptile. The great sauropods would have munched their way through the Mesozoic like herds of elephants. Dinosaurs the size of elephants, such as Triceratops, would have eaten like a bison. A big carnivore, such as Tyrannosaurus, would have needed as much meat as a lion. A dead Triceratops would have lasted one for months, or until it went putrid. It is more likely they hunted in packs and shared it.
Of course, once the asteroid struck, they all became extinct. The world was inherited by the mammals, which cannot grow any larger than Paraceratherium, and even it was an outlier. The really gigantic monsters will never be seen again.
Here's another look at the issue.
The next chapter is Geological and Historical Time.
Or click to return to the Index.
Wednesday 6 August 2014
Geological and Historical Time
The second most common mistake in science fiction is the time frame of extraterrestrial civilisations. Let's look at it this way. Some fields of science, such as astronomy and biology, are open-ended. There will always be something new to discover. Indeed, the subjects will be changing as we watch them. But when it comes to physics and chemistry, there must come a time when we will literally know everything about the basic functioning of the universe. After that, it will just be a matter of fine-tuning the technology we already produce. We will have reached a technological plateau. How long will this take? Another hundred years? Another thousand? In any case, that is the order of magnitude of the time scale.
Now let us ask a second question: how old is civilisation? It depends on what you mean by the term. Agriculture first arose at various points about 11,000 or 12,000 years ago. However, primitive versions of it, such as the Melanesian garden economies or the Maasai cattle herding are scarcely what most people would call "civilised". The first city, Uruk arose about 6,000 years ago. Even then, the vast majority of the world's population were still hunter gatherers - as was the whole of the human race for most of its history. Homo sapiens itself is about 200,000 years old. If aliens had seen our ancestors half a million years ago, they might have declared there was no intelligent life on earth, even if some species showed promise.
A third question: how long does it take for intelligent life to evolve? For that matter, how long is a piece of string? If an asteroid hadn't wiped out the dinosaurs 65½ million years ago, they would probably still be around. They would have seen some hard times, but there was nothing which would have caused them to go extinct, and no obvious reason any of them should evolve humanlike intelligence. On the other hand, if the asteroid had arrived 50 million years earlier, it would have kicked started the age of mammals by 50 million years, but not necessarily the evolution of intelligent life. That requires a special set of environmental circumstances. The chance might have been lost completely.
The fact is that there is no way of predicting when intelligent life will evolve, because life forms, like technology, advance faster as they become more complex. The earth is about 4,600 million years old - and there are stars, and presumably planets, even older. For the first 800 million years it was completely lifeless. After that, for the majority of its history, life was restricted to tiny, even microscopic forms. It was only about 600 million years ago that simple, multicellular organisms of any size appear in the fossil record.
In the evolution of intelligent life, let us assume that no planet can be more than 100 million years "behind" us or "ahead of" us. This, I am sure, is a gross underestimate. Let us also assume that it requires 10,000 years of civilisation before a technological plateau is reached. Of that, 6,000 years has already passed on earth, and we need another 4,000 years to reach it.
That means that, when we finally head off into the stars, half the living planets will be at an earlier stage than ours. Some of them will be stuck in the age of reptiles 100 million years ago. Some others will have primitive intelligent life forms such as evolved half a million years ago on earth. A quick calculation will reveal that they will form just half of one percent of the total. If we think of those civilisations comparable to those which have arisen in the last 6,000 years on earth, they will be present in only 0.0006% of cases.
Of course, that's just the half which are "behind" us. What would we find in the other half? Well, we wouldn't find them; they'd find us. If UFOs are what we think they are, they already have. Half the living planets in the galaxy will be occupied by civilisations more advanced than ours. Of these, all but 0.0004% will have already reached the technological plateau. And that's putting it mildly. It assumes that they all stay on their own planets. It is far more likely that they will colonise other planets before we reach them. Have no doubt about it: any intelligent life forms we encounter out there will be far, far more advanced than us, usually by millions of years.
This, you might note, is the reverse of what is portrayed in much of science fiction, especially the "space opera" type. Look at Star Trek. They were regularly encountering civilisations with technologies only 100 years or so in advance of ours - or 100 years behind us. That's not how it's going to be. The Vulcans and the Romulans would have possessed technologies which would make our science look like children's toys. We might meet a few species still running around clad in fur and throwing spears, but not very many. We are the babies of the galaxy. The others out there are probably watching us as something special: the first new civilisation to come along in a long time.
There is one more objection people might make: what if the more advanced civilisations have become extinct? That would simply mean more space for those which did not go extinct to expand into - because it is highly unlikely that every single one would go extinct.
But it might be more germane to ask exactly what could cause the extinction of an advanced civilisation, especially one which has reached the technological plateau? It is natural that these doomsday scenarios would proliferate during the second half of last century, when we lived under the threat of nuclear war, and when societies awoke to the prospect of ecological dangers. But consider it cold-bloodedly. If a nuclear war had taken place a few decades ago, it would certainly have devastated the Northern Hemisphere. A lot would depend on whether China took part in it. The economies of the rest of the world would have collapsed. Some backward societies, such as Africa, would probably have reverted to barbarism. But the human race would not have become extinct. And in isolated areas, such as New Zealand, civilisation would still have continued, as the seeds of a new civilisation. So the doomsayers would have to assume that every time civilisation made a comeback, it would destroy itself again. That's a pretty big assumption - especially if it applied to every intelligent species in the galaxy. After all, we missed it the first time round!
What about ecological collapse? Global warming would not destroy civilisation, let alone humanity. No, there is no need to "deny" the science. The worst case scenario is that the situation would become so dire that, eventually, the world would have to stop everything and fix it up - just as we did during the two World Wars. This is the fatal flaw of all the eco-apocalyptic scenarios: economics and sheer inconvenience will cut in long before total destruction.
Anything else? If another asteroid such as destroyed the dinosaurs were to have struck 100 years ago, it well might have wiped out the human race. But if it were to approach next year, we would see it coming, and at least take action to permit a nucleus of us to survive. If we saw it coming 100 years from now, we would be able to intercept it. Besides, it's not as if such disasters are a regular occurrence. The last one happened 65½ million years ago, and it appears to have been the only one.
No. Take my word for it: once high civilisations arise, they will be around for millions of years, if not forever. And they're the ones we are going to encounter.
The next chapter will be Interplanetary Hybrids.
Or you can return to the Index.
Now let us ask a second question: how old is civilisation? It depends on what you mean by the term. Agriculture first arose at various points about 11,000 or 12,000 years ago. However, primitive versions of it, such as the Melanesian garden economies or the Maasai cattle herding are scarcely what most people would call "civilised". The first city, Uruk arose about 6,000 years ago. Even then, the vast majority of the world's population were still hunter gatherers - as was the whole of the human race for most of its history. Homo sapiens itself is about 200,000 years old. If aliens had seen our ancestors half a million years ago, they might have declared there was no intelligent life on earth, even if some species showed promise.
A third question: how long does it take for intelligent life to evolve? For that matter, how long is a piece of string? If an asteroid hadn't wiped out the dinosaurs 65½ million years ago, they would probably still be around. They would have seen some hard times, but there was nothing which would have caused them to go extinct, and no obvious reason any of them should evolve humanlike intelligence. On the other hand, if the asteroid had arrived 50 million years earlier, it would have kicked started the age of mammals by 50 million years, but not necessarily the evolution of intelligent life. That requires a special set of environmental circumstances. The chance might have been lost completely.
The fact is that there is no way of predicting when intelligent life will evolve, because life forms, like technology, advance faster as they become more complex. The earth is about 4,600 million years old - and there are stars, and presumably planets, even older. For the first 800 million years it was completely lifeless. After that, for the majority of its history, life was restricted to tiny, even microscopic forms. It was only about 600 million years ago that simple, multicellular organisms of any size appear in the fossil record.
In the evolution of intelligent life, let us assume that no planet can be more than 100 million years "behind" us or "ahead of" us. This, I am sure, is a gross underestimate. Let us also assume that it requires 10,000 years of civilisation before a technological plateau is reached. Of that, 6,000 years has already passed on earth, and we need another 4,000 years to reach it.
That means that, when we finally head off into the stars, half the living planets will be at an earlier stage than ours. Some of them will be stuck in the age of reptiles 100 million years ago. Some others will have primitive intelligent life forms such as evolved half a million years ago on earth. A quick calculation will reveal that they will form just half of one percent of the total. If we think of those civilisations comparable to those which have arisen in the last 6,000 years on earth, they will be present in only 0.0006% of cases.
Of course, that's just the half which are "behind" us. What would we find in the other half? Well, we wouldn't find them; they'd find us. If UFOs are what we think they are, they already have. Half the living planets in the galaxy will be occupied by civilisations more advanced than ours. Of these, all but 0.0004% will have already reached the technological plateau. And that's putting it mildly. It assumes that they all stay on their own planets. It is far more likely that they will colonise other planets before we reach them. Have no doubt about it: any intelligent life forms we encounter out there will be far, far more advanced than us, usually by millions of years.
This, you might note, is the reverse of what is portrayed in much of science fiction, especially the "space opera" type. Look at Star Trek. They were regularly encountering civilisations with technologies only 100 years or so in advance of ours - or 100 years behind us. That's not how it's going to be. The Vulcans and the Romulans would have possessed technologies which would make our science look like children's toys. We might meet a few species still running around clad in fur and throwing spears, but not very many. We are the babies of the galaxy. The others out there are probably watching us as something special: the first new civilisation to come along in a long time.
There is one more objection people might make: what if the more advanced civilisations have become extinct? That would simply mean more space for those which did not go extinct to expand into - because it is highly unlikely that every single one would go extinct.
But it might be more germane to ask exactly what could cause the extinction of an advanced civilisation, especially one which has reached the technological plateau? It is natural that these doomsday scenarios would proliferate during the second half of last century, when we lived under the threat of nuclear war, and when societies awoke to the prospect of ecological dangers. But consider it cold-bloodedly. If a nuclear war had taken place a few decades ago, it would certainly have devastated the Northern Hemisphere. A lot would depend on whether China took part in it. The economies of the rest of the world would have collapsed. Some backward societies, such as Africa, would probably have reverted to barbarism. But the human race would not have become extinct. And in isolated areas, such as New Zealand, civilisation would still have continued, as the seeds of a new civilisation. So the doomsayers would have to assume that every time civilisation made a comeback, it would destroy itself again. That's a pretty big assumption - especially if it applied to every intelligent species in the galaxy. After all, we missed it the first time round!
What about ecological collapse? Global warming would not destroy civilisation, let alone humanity. No, there is no need to "deny" the science. The worst case scenario is that the situation would become so dire that, eventually, the world would have to stop everything and fix it up - just as we did during the two World Wars. This is the fatal flaw of all the eco-apocalyptic scenarios: economics and sheer inconvenience will cut in long before total destruction.
Anything else? If another asteroid such as destroyed the dinosaurs were to have struck 100 years ago, it well might have wiped out the human race. But if it were to approach next year, we would see it coming, and at least take action to permit a nucleus of us to survive. If we saw it coming 100 years from now, we would be able to intercept it. Besides, it's not as if such disasters are a regular occurrence. The last one happened 65½ million years ago, and it appears to have been the only one.
No. Take my word for it: once high civilisations arise, they will be around for millions of years, if not forever. And they're the ones we are going to encounter.
The next chapter will be Interplanetary Hybrids.
Or you can return to the Index.
Interplanetary Hybrids
What do you get if you cross a kangaroo with a sheep? Nothing! Everybody knows that unrelated species cannot interbreed. So why do we so often read accounts of interplanetary hybrids? And why are they always between human beings and some vaguely humanoid alien? Why don't they cross earthly dogs with extraterrestrial canines for a change?
Here on earth there are three barriers to interspecific hybridisation: behavioural, functional, and genetic. Behavioural is rather obvious; in the vast majority of cases different species are not sexually attracted to each other, and do not attempt to interbreed. If they do, it is usually in captivity, when they lack possible mates of their own species.
Consider, now, the situation where the parents come from different planets, and their body plans have a completely different evolutionary history. It is possible to conceive of a humanoid alien which looks just the same as a human being (an unlikely event, I will admit, but theoretically possible) while being completely different on the inside, because it possible to construct the same body plan with totally different components. The examples I am about to provide are by no means exhaustive.
First of all, we might start with something which is utterly fundamental, but of which hardly anyone is aware: optical rotation. Living organisms are carbon-based because carbon has a valence of four, meaning that each atom can bond with a maximum of four other atoms. Since two of those atoms can also be carbon, long chains of carbon atoms are possible. Now, let us visualise one carbon atom in the middle of a chain. It is bonded to another carbon atom at each end, and two other atoms - let us call them "A" and "B" sticking out of the sides. It is obvious that they can be attached in two different manners: with A to the right, or with B to the right. The molecule can thus exist in two forms, which are mirror images of each other. In biochemistry, they are classified as "dextro" (D) or right-handed, and "laevo" (L) or left-handed. They often possess very different chemical properties.
The point is that, although artificially synthesized drugs typically contain more or less equal quantities of D and L molecules, living organisms produce only L molecules. That is, here on earth. It is a result of the way life first developed at the dawn of time. But that was just a fluke. On another planet everything might well be constructed on D molecules. Indeed, I cannot see any reason why half the living planets shouldn't contain L-life and the other half D-life.
Let's look at a few other features. Many birds, such as parrots, can copy human speak and so, if they were clever enough, they would be able to talk. However, their voice boxes are quite different from ours. Instead of vibrating a pair of vocal chords, they vibrate a type of drum in an organ called a syrinx.
The eyes of a mollusc, such as a giant squid, and those of a vertebrate, such as us, look very similar, and they function just as effectively. However, the rear of the eye is structured quite differently in the two groups. And while we are on the subject of eyesight, we might mention colour vision. The back part of our eye contains cells called cones, with pigments in three different colours: red, green, and blue. We can distinguish a million separate colours by matching the incoming light against the proportion absorbed by each of the pigments. Colour blind humans usually have one of the pigments out of kilter with the others, and less often lack one of the pigments. It would be incredible if an alien had exactly the same pigments as us. But most mammals possess only two pigments. Contrary to what you may have heard, they do not see the world in black and white, but they do lack the red pigment. But most birds, reptiles, and amphibians, not to mention most insects, have four pigments. Some, especially among the insects, can see in the ultraviolet.
Much of our anatomy is the result of evolutionary accidents. Why, for example, should an alien's organ of balance be attached to the ear, as ours is (the inner ear)? Why should it possess only seven vertebrae in its neck, as almost all mammals do? Why twelve pairs of ribs? Our skulls consist of a mosaic of bones, which need not be the same in an alien humanoid. Some of these bones are normal, run-of-the-mill internal bones, and some develop by ossifications in the skin.
It is the endocrine system which is the most arbitrary in position and formation. Because these glands feed hormones directly into the bloodstream, they could logically be placed anywhere in the body cavity. Our thymus, for instance, is where it is because it evolved from a mucus-secreting gland in the pharynx of an ancient ancestor in the days before backbones were invented. There is no reason, other than evolutionary history, why the pituitary gland should be placed under the braincase, or the adrenals on top of the kidneys. Indeed, there is no reason why their functions ie the hormones they produce, should not been spread out among a whole lot of different glands placed all over the body.
Sex. I could list many more examples, but since sex will always catch people's attention, let's discuss the "naughty bits". Essentially, they start off in the embryo as a combination of a pair of sex glands (testes or ovaries), and a pair of tubes which allows the products (sperm, eggs or, in the case of mammals, babies) to pass to the outside world. In men, it is the Wolffian duct, in women the Müllerian duct. However, a tube, known as the urethra is also required to pass urine from the bladder to outside world. They tend to join up before they reach the outside, which is why we urinate and copulate through the same orifice. But marsupials (mammals with a pouch) and placentals (mammals like us) differ in the placement of the sex ducts and the urethra. And this leads to some interesting results.
In male placentals, the urethra comes in front of the Wolffian duct, in marsupials it comes in behind. That means that in marsupials the testicles descend in front of the penis, rather than behind it, as we assume is normal. (The testicles descend to allow them to be cool enough for the sperm to grow.)
In females, the Müllerian ducts swell up in sections to become vaginas, uteri (wombs), and Fallopian tubes. Among placentals, the Müllerian ducts come in between the urethras, a position which allows the ducts to fuse. First they fuse at the near end, resulting in a single vagina. Then the sections which will later form a uterus get a chance to fuse. In some species which give birth to large litters, this doesn't happen; from the cervix, two separate uteri diverge, each capable of implanting several embryos. In others, the near ends fuse, resulting in a single uterus with two horns. The final result is that found in humans, with the ducts completely fused to produce a single uterus.
The situation is quite different, however, in marsupials. There, the urethras come in between the Müllerian ducts, making fusion impossible. Marsupials therefore possess a double internal vagina. The inevitable result is that the male's penis is forked.
Bats, carnivores, insectivores, rodents, and other primates (monkeys and apes) have a bone in the penis. In many species the penis is decorated with spines and/or various folds and frills. (If you are wondering why, they increase sensitivity, allowing a speedy ejaculation, something not necessary, and even counterproductive in a monogamous species.) Mammals display three different types of penis: a vascular one, as in humans and horses, a fibrous one, as in bulls, and an intermediate type, as in rats. Reptiles possess two half-penes, and most birds don't have any at all.
But even that implies that the species are closely related. It is well known that humans share more than 98% of our genes with chimpanzees. (We also share about a third of them with the cabbage, but that's seldom mentioned.) But the number of genes shared with an alien from Alpha Centauri is zero, zip, zilch. They cannot mix. Full stop. Exclamation mark.
But there's more. You probably also know that genes are made up of DNA. DNA is a string of four types of nucleotides, labelled A, C, G, and T. Proteins, on the other hand, are strings of twenty different types of amino acids. The DNA in your genes is responsible for the manufacture of proteins, each amino acid being represented by one or more codons of three nucleotides. Since the possible number of combinations of three nucleotides is 4 x 4 x 4 = 64, and there are only 20 amino acids, plus a start sign and stop sign, a certain amount of redundancy exists. For example, both AAT and AAC code for the amino acid, asparagine.
The important thing to understand, however, is that this genetic code is completely arbitrary. There is no good reason by any set of three nucleotides should code for any particular amino acid. The code we have is to one that arose on earth when life first developed from the primordial soup, and it will continue until the last days of earthly life. However, by the laws of chance, the genetic code on any other planet will be different - and that's assuming that the unearthly life forms use DNA at all. Reproduction between the two would be totally impossible. Even splicing an earthly gene into an alien microbe to produce a genetically modified microbe would be impossible.
Nevertheless, there is one last objection. If you follow the literature on UFOs, and particularly alien abductions, you will be aware of claims of alien-human hybrids being encountered. Well, all I can say is that people claim to have seen beings which they interpret as alien-human hybrids. That's not the same thing.
Now, do you think it is possible for two intelligent, technological species to evolve on the same planet, as many scifi stories suggest? If so, click here.
Otherwise, go back to the Index.
Here on earth there are three barriers to interspecific hybridisation: behavioural, functional, and genetic. Behavioural is rather obvious; in the vast majority of cases different species are not sexually attracted to each other, and do not attempt to interbreed. If they do, it is usually in captivity, when they lack possible mates of their own species.
Functional Barriers
In point of fact, closely related species can interbreed, and sometimes the offspring are fertile. However, often there is some defect present. Crosses between lions and tigers, for example, tend to be huge. It is like a mechanic replacing one part of an automobile engine with the analogous part of another make. If the two makes are similar, the result will be reasonably successful. If they are different, the engine will perform poorly. If they are too different, it will not run at all. But the real analogy would be the replacement, not of a single part, but half of them.Consider, now, the situation where the parents come from different planets, and their body plans have a completely different evolutionary history. It is possible to conceive of a humanoid alien which looks just the same as a human being (an unlikely event, I will admit, but theoretically possible) while being completely different on the inside, because it possible to construct the same body plan with totally different components. The examples I am about to provide are by no means exhaustive.
First of all, we might start with something which is utterly fundamental, but of which hardly anyone is aware: optical rotation. Living organisms are carbon-based because carbon has a valence of four, meaning that each atom can bond with a maximum of four other atoms. Since two of those atoms can also be carbon, long chains of carbon atoms are possible. Now, let us visualise one carbon atom in the middle of a chain. It is bonded to another carbon atom at each end, and two other atoms - let us call them "A" and "B" sticking out of the sides. It is obvious that they can be attached in two different manners: with A to the right, or with B to the right. The molecule can thus exist in two forms, which are mirror images of each other. In biochemistry, they are classified as "dextro" (D) or right-handed, and "laevo" (L) or left-handed. They often possess very different chemical properties.
The point is that, although artificially synthesized drugs typically contain more or less equal quantities of D and L molecules, living organisms produce only L molecules. That is, here on earth. It is a result of the way life first developed at the dawn of time. But that was just a fluke. On another planet everything might well be constructed on D molecules. Indeed, I cannot see any reason why half the living planets shouldn't contain L-life and the other half D-life.
Let's look at a few other features. Many birds, such as parrots, can copy human speak and so, if they were clever enough, they would be able to talk. However, their voice boxes are quite different from ours. Instead of vibrating a pair of vocal chords, they vibrate a type of drum in an organ called a syrinx.
The eyes of a mollusc, such as a giant squid, and those of a vertebrate, such as us, look very similar, and they function just as effectively. However, the rear of the eye is structured quite differently in the two groups. And while we are on the subject of eyesight, we might mention colour vision. The back part of our eye contains cells called cones, with pigments in three different colours: red, green, and blue. We can distinguish a million separate colours by matching the incoming light against the proportion absorbed by each of the pigments. Colour blind humans usually have one of the pigments out of kilter with the others, and less often lack one of the pigments. It would be incredible if an alien had exactly the same pigments as us. But most mammals possess only two pigments. Contrary to what you may have heard, they do not see the world in black and white, but they do lack the red pigment. But most birds, reptiles, and amphibians, not to mention most insects, have four pigments. Some, especially among the insects, can see in the ultraviolet.
Much of our anatomy is the result of evolutionary accidents. Why, for example, should an alien's organ of balance be attached to the ear, as ours is (the inner ear)? Why should it possess only seven vertebrae in its neck, as almost all mammals do? Why twelve pairs of ribs? Our skulls consist of a mosaic of bones, which need not be the same in an alien humanoid. Some of these bones are normal, run-of-the-mill internal bones, and some develop by ossifications in the skin.
It is the endocrine system which is the most arbitrary in position and formation. Because these glands feed hormones directly into the bloodstream, they could logically be placed anywhere in the body cavity. Our thymus, for instance, is where it is because it evolved from a mucus-secreting gland in the pharynx of an ancient ancestor in the days before backbones were invented. There is no reason, other than evolutionary history, why the pituitary gland should be placed under the braincase, or the adrenals on top of the kidneys. Indeed, there is no reason why their functions ie the hormones they produce, should not been spread out among a whole lot of different glands placed all over the body.
Sex. I could list many more examples, but since sex will always catch people's attention, let's discuss the "naughty bits". Essentially, they start off in the embryo as a combination of a pair of sex glands (testes or ovaries), and a pair of tubes which allows the products (sperm, eggs or, in the case of mammals, babies) to pass to the outside world. In men, it is the Wolffian duct, in women the Müllerian duct. However, a tube, known as the urethra is also required to pass urine from the bladder to outside world. They tend to join up before they reach the outside, which is why we urinate and copulate through the same orifice. But marsupials (mammals with a pouch) and placentals (mammals like us) differ in the placement of the sex ducts and the urethra. And this leads to some interesting results.
In male placentals, the urethra comes in front of the Wolffian duct, in marsupials it comes in behind. That means that in marsupials the testicles descend in front of the penis, rather than behind it, as we assume is normal. (The testicles descend to allow them to be cool enough for the sperm to grow.)
In females, the Müllerian ducts swell up in sections to become vaginas, uteri (wombs), and Fallopian tubes. Among placentals, the Müllerian ducts come in between the urethras, a position which allows the ducts to fuse. First they fuse at the near end, resulting in a single vagina. Then the sections which will later form a uterus get a chance to fuse. In some species which give birth to large litters, this doesn't happen; from the cervix, two separate uteri diverge, each capable of implanting several embryos. In others, the near ends fuse, resulting in a single uterus with two horns. The final result is that found in humans, with the ducts completely fused to produce a single uterus.
The situation is quite different, however, in marsupials. There, the urethras come in between the Müllerian ducts, making fusion impossible. Marsupials therefore possess a double internal vagina. The inevitable result is that the male's penis is forked.
Bats, carnivores, insectivores, rodents, and other primates (monkeys and apes) have a bone in the penis. In many species the penis is decorated with spines and/or various folds and frills. (If you are wondering why, they increase sensitivity, allowing a speedy ejaculation, something not necessary, and even counterproductive in a monogamous species.) Mammals display three different types of penis: a vascular one, as in humans and horses, a fibrous one, as in bulls, and an intermediate type, as in rats. Reptiles possess two half-penes, and most birds don't have any at all.
Genetic Barriers
By now you should have gathered than interplanetary hybridisation is as likely as splicing together a motorcycle engine and a diesel engine, and expecting it to work. But the real problem is genetic. As has been explained before, closely related species can interbreed, but the offspring tend to be non-adaptive. Often they are also infertile. Probably most of you know that genetic information is carried on genes, and that the genes are carried on bodies called chromosomes, which each of us possess in duplicate, one set from each parent. The genes of a horses and a donkey are similar enough to produce viable offspring, a mule. However, the horse's genes are carried on 32 pairs of chromosomes, and the very similar genes on the donkey's 31 pairs. The poor old mule thus received an odd number of chromosomes. If it tries to mate with another mule, or with a donkey or horse, its offspring will have either one too many or one too few chromosomes, and it will not develop.But even that implies that the species are closely related. It is well known that humans share more than 98% of our genes with chimpanzees. (We also share about a third of them with the cabbage, but that's seldom mentioned.) But the number of genes shared with an alien from Alpha Centauri is zero, zip, zilch. They cannot mix. Full stop. Exclamation mark.
But there's more. You probably also know that genes are made up of DNA. DNA is a string of four types of nucleotides, labelled A, C, G, and T. Proteins, on the other hand, are strings of twenty different types of amino acids. The DNA in your genes is responsible for the manufacture of proteins, each amino acid being represented by one or more codons of three nucleotides. Since the possible number of combinations of three nucleotides is 4 x 4 x 4 = 64, and there are only 20 amino acids, plus a start sign and stop sign, a certain amount of redundancy exists. For example, both AAT and AAC code for the amino acid, asparagine.
The important thing to understand, however, is that this genetic code is completely arbitrary. There is no good reason by any set of three nucleotides should code for any particular amino acid. The code we have is to one that arose on earth when life first developed from the primordial soup, and it will continue until the last days of earthly life. However, by the laws of chance, the genetic code on any other planet will be different - and that's assuming that the unearthly life forms use DNA at all. Reproduction between the two would be totally impossible. Even splicing an earthly gene into an alien microbe to produce a genetically modified microbe would be impossible.
Nevertheless, there is one last objection. If you follow the literature on UFOs, and particularly alien abductions, you will be aware of claims of alien-human hybrids being encountered. Well, all I can say is that people claim to have seen beings which they interpret as alien-human hybrids. That's not the same thing.
Now, do you think it is possible for two intelligent, technological species to evolve on the same planet, as many scifi stories suggest? If so, click here.
Otherwise, go back to the Index.
Tuesday 5 August 2014
Two Intelligent Species
If you intend to open a restaurant, you ought to check the local competition. If there is a Chinese restaurant in the neighourhood, you might consider opening an Italian restaurant. Or you could open a fast food eatery in an area overflowing with expensive, high-class restaurants. But if there are too many restaurants in the area, one of them is going to go to the wall.
What you need to understand is that the same applies to biology. A species' way of life is called its niche, and natural selection ensures that individual niches do not overlap too much. There are two species of rhinoceros living side by side in Africa, but one is a grazer and the other is a browser, so they get on well enough. When you watch one of those African documentaries, you should be aware that every species of gazelle, antelope, wildebeest, buffalo, or zebra consumes a slightly different type of food or exploits a slightly different microenvironment. In archipelagos it is not uncommon for two similar species to exist on one island, but only a single species on another. In the latter case, it is normal for the single species to expand its niche to include much of what the other one would have occupied. That is why the biggest leopards in the world live in Sri Lanka; there are no tigers there. If two species occupy the same niche, the less efficient one will go to the wall. Because of this the thylacine became extinct on mainland Australia once the dingo arrived, and why the British red squirrel is retreating before the advance of the introduced grey squirrel.
So what would happen if two species each occupied an extremely broad niche - like intelligent, tool-making generalist, similar to Homo sapiens? Can two intelligent species, particularly unrelated ones, evolve on the same planet? A lot of science fiction writers seem to think so.
But we don't need to ask, because it has already happened. Between 400,000 and 800,000 years ago, the human lineage split. Those in Africa evolved into us, those in Eurasia into the Neanderthals. In the last few years, a brand new species, a branch-off from the Neanderthals, has been discovered in Siberia: the Denisovans, named for the cave in which it was found. It is also likely that a strange group of fossils in the Red Deer Cave of China may have been another species. It is becoming ever more obvious that a number of small twigs of the human family tree once developed into fully-fledged species. But, by and large, the two most successful species, the ones which occupied the broadest territory for the longest period, were Homo sapiens and Homo neanderthalensis.
But now there is only one. They came into contact 60 or 70,000 years ago, when our ancestors left Africa, and by about 28,000 years ago the Neanderthals were extinct. We did not exterminate them. Over those 30 or 40 millennia, the two species would have run the full gamut of interactions, from violence, to avoidance, and to friendship. We even mated with them. It is now established that while black Africans interbred with other archaic humans, the rest of us all possess a few percentages of Neanderthal genes (and Australian Aborigines have Denisovan genes as well). However, the two species occupied the same niche, they were competing for the same resources, and one of them had to go. It has been calculated that a 2% inferiority in breeding success would have put the Neanderthals on a downward spiral to extinction.
In popular culture the Neanderthals have been visualised as dull, brutish first attempts by nature at her program of evolving her pièce de résistance: us. This is not true. The Neanderthals were as human as us, but a different type of humanity. They had bigger brains than ours. Estimating their IQ is impossible, but it is likely that any deficiency in comparison to Homo sapiens would be in an ability the IQ tests cannot measure: creativity. Left to themselves, they would probably in time have discovered agriculture and developed civilisation. They did, however, possess two characteristics of our ape ancestors which we have lost. Firstly, they were incredibly strong. Secondly, they grew and aged faster - more like a chimpanzee than a modern human. A five-year-old child looked like an eight-year-old modern human, a 40-year-old was as decrepit as a 70-year-old. They could have outbred us. On the other hand, each generation had less time to learn and to pass on its skills and invent new ones. When the crunch came, this may have been where our advantage lay.
So there you have it: two major and one or two minor intelligent species evolved on the same planet, and all but one became extinct while they were all in the hunter gatherer stage. It is possible to imagine other scenarios. Suppose the Denisovans got to Australia first, and then the continent became, by some geological quirk, completely isolated until modern times. Then, when the first European settlers arrived in the eighteenth century, they would have found it occupied, not by Stone Age Homo sapiens, but by some mysterious separate species of humanity, also in the Stone Age. (Agriculture and of civilisation require certain preconditions such that, although they can arise more than once, they will do so on different time scales. Added to this the different abilities and intelligence of different species, and it is next to impossible that two species will achieve technological equivalence simultaneously.)
Africa and Ice Age Eurasia were poor ground for the development of agriculture, which commenced first in the post-glacial Middle East. But suppose Africa and Eurasia were somehow isolated at the end of the Ice Age, such that the Neanderthals discovered agriculture first. Would they have eventually moved into Africa, and outcompeted our species, leading to our extinction - or perhaps leaving a remnant population of Homo sapiens in the jungles of West Africa, whose horrible diseases would keep out the Neanderthals as they once made it the "white man's grave"? Or is our species really superior under all conditions, such that once we had learned agriculture from the Neanderthals, we still managed to push them to extinction?
These scenarios are about the best a realistic science fiction writer can offer. But modern humans and Neanderthals were closely related. What about the evolution of two unrelated intelligent species? Suppose the Americas were completely isolated from Eurasia, so that when Columbus finally arrived, he found, not Indians, but a second human-equivalent which had evolved from the New World monkeys? Forget it! That would imply that two parallel streams of evolution advanced at the same rate. Refer back to my article on geological and historical time. The evolution of intelligent life forms is probably inevitable once life begins, but it still requires specific conditions to ignite it, and the chances of it happening simultaneously twice on different continents are so remote they are effectively non-existent.
No! You may rest assured that when we finally discover intelligent life in outer space, it will have evolved just once per planet.
Now click here to examine the problems of extreme longevity.
Or return to the Index.
What you need to understand is that the same applies to biology. A species' way of life is called its niche, and natural selection ensures that individual niches do not overlap too much. There are two species of rhinoceros living side by side in Africa, but one is a grazer and the other is a browser, so they get on well enough. When you watch one of those African documentaries, you should be aware that every species of gazelle, antelope, wildebeest, buffalo, or zebra consumes a slightly different type of food or exploits a slightly different microenvironment. In archipelagos it is not uncommon for two similar species to exist on one island, but only a single species on another. In the latter case, it is normal for the single species to expand its niche to include much of what the other one would have occupied. That is why the biggest leopards in the world live in Sri Lanka; there are no tigers there. If two species occupy the same niche, the less efficient one will go to the wall. Because of this the thylacine became extinct on mainland Australia once the dingo arrived, and why the British red squirrel is retreating before the advance of the introduced grey squirrel.
So what would happen if two species each occupied an extremely broad niche - like intelligent, tool-making generalist, similar to Homo sapiens? Can two intelligent species, particularly unrelated ones, evolve on the same planet? A lot of science fiction writers seem to think so.
But we don't need to ask, because it has already happened. Between 400,000 and 800,000 years ago, the human lineage split. Those in Africa evolved into us, those in Eurasia into the Neanderthals. In the last few years, a brand new species, a branch-off from the Neanderthals, has been discovered in Siberia: the Denisovans, named for the cave in which it was found. It is also likely that a strange group of fossils in the Red Deer Cave of China may have been another species. It is becoming ever more obvious that a number of small twigs of the human family tree once developed into fully-fledged species. But, by and large, the two most successful species, the ones which occupied the broadest territory for the longest period, were Homo sapiens and Homo neanderthalensis.
But now there is only one. They came into contact 60 or 70,000 years ago, when our ancestors left Africa, and by about 28,000 years ago the Neanderthals were extinct. We did not exterminate them. Over those 30 or 40 millennia, the two species would have run the full gamut of interactions, from violence, to avoidance, and to friendship. We even mated with them. It is now established that while black Africans interbred with other archaic humans, the rest of us all possess a few percentages of Neanderthal genes (and Australian Aborigines have Denisovan genes as well). However, the two species occupied the same niche, they were competing for the same resources, and one of them had to go. It has been calculated that a 2% inferiority in breeding success would have put the Neanderthals on a downward spiral to extinction.
In popular culture the Neanderthals have been visualised as dull, brutish first attempts by nature at her program of evolving her pièce de résistance: us. This is not true. The Neanderthals were as human as us, but a different type of humanity. They had bigger brains than ours. Estimating their IQ is impossible, but it is likely that any deficiency in comparison to Homo sapiens would be in an ability the IQ tests cannot measure: creativity. Left to themselves, they would probably in time have discovered agriculture and developed civilisation. They did, however, possess two characteristics of our ape ancestors which we have lost. Firstly, they were incredibly strong. Secondly, they grew and aged faster - more like a chimpanzee than a modern human. A five-year-old child looked like an eight-year-old modern human, a 40-year-old was as decrepit as a 70-year-old. They could have outbred us. On the other hand, each generation had less time to learn and to pass on its skills and invent new ones. When the crunch came, this may have been where our advantage lay.
So there you have it: two major and one or two minor intelligent species evolved on the same planet, and all but one became extinct while they were all in the hunter gatherer stage. It is possible to imagine other scenarios. Suppose the Denisovans got to Australia first, and then the continent became, by some geological quirk, completely isolated until modern times. Then, when the first European settlers arrived in the eighteenth century, they would have found it occupied, not by Stone Age Homo sapiens, but by some mysterious separate species of humanity, also in the Stone Age. (Agriculture and of civilisation require certain preconditions such that, although they can arise more than once, they will do so on different time scales. Added to this the different abilities and intelligence of different species, and it is next to impossible that two species will achieve technological equivalence simultaneously.)
Africa and Ice Age Eurasia were poor ground for the development of agriculture, which commenced first in the post-glacial Middle East. But suppose Africa and Eurasia were somehow isolated at the end of the Ice Age, such that the Neanderthals discovered agriculture first. Would they have eventually moved into Africa, and outcompeted our species, leading to our extinction - or perhaps leaving a remnant population of Homo sapiens in the jungles of West Africa, whose horrible diseases would keep out the Neanderthals as they once made it the "white man's grave"? Or is our species really superior under all conditions, such that once we had learned agriculture from the Neanderthals, we still managed to push them to extinction?
These scenarios are about the best a realistic science fiction writer can offer. But modern humans and Neanderthals were closely related. What about the evolution of two unrelated intelligent species? Suppose the Americas were completely isolated from Eurasia, so that when Columbus finally arrived, he found, not Indians, but a second human-equivalent which had evolved from the New World monkeys? Forget it! That would imply that two parallel streams of evolution advanced at the same rate. Refer back to my article on geological and historical time. The evolution of intelligent life forms is probably inevitable once life begins, but it still requires specific conditions to ignite it, and the chances of it happening simultaneously twice on different continents are so remote they are effectively non-existent.
No! You may rest assured that when we finally discover intelligent life in outer space, it will have evolved just once per planet.
Now click here to examine the problems of extreme longevity.
Or return to the Index.
Teeth, Brains, and the Elixir of Youth
I take good care of my teeth. I have required only two, maybe three, small fillings since I was eight. But a couple of years ago a shard fell off one of my lower incisors when I took a bite. When I visited the dentist, he told me the same thing was about to happen to two others, and that he would need to cap them, just as he once capped my canines, which had been worn level to the incisors over the years.
"My teeth are getting old," I said. "They've been biting for the almost fifty-five years."
That got me thinking about the eternal quest for an elixir of youth, or some formula for the great extension of human life, and how the inventors of these schemes never think about teeth and brains.
First of all, so complex is the human body that it is hardly imaginable that ageing can be fought with a simple, one-off treatment, or even a simple periodic treatment. "Youth therapy", as I shall call it would have to entail a carefully managed cocktail of drugs, and possibly physical therapies, applied over the whole of one's life, and replete with a whole raft of side effects.
The causes of ageing are not known, but some hypotheses include the shortening of telomeres with each cell division, damage caused by free radicals produced by that essential poison, oxygen, the accumulation of wastes, and so forth. No doubt many factors are involved. But all of them boil down to the same truism: no system is perfect. The chemical composition of your body changes with every breath you inhale or exhale, every bite you take, and any movement you perform. Your body is like a waterfall: forever changing, and forever attempting to maintain its form. It is constantly wearing out and constantly repairing itself. But because the process is not 100% perfect, the wear and tear will eventually overtake the repair.
It is important to understand that not all non-infectious disorders are due to ageing. When wear and tear overtake repair in the joints, we call it arthritis. Youth therapy would slow it down, but obesity, long term heavy lifting, and a severe injury to the joint will all tip the scales towards arthritis; if you live long enough, it will catch up with you. Age will weaken the heart, but so will obesity, lack of exercise, smoking, and hypertension. Youth therapy may prevent hypertension under normal circumstances, but if you consume too much alcohol or salt it will catch up with you. Ageing thins the skin and leads to wrinkles, but so does sun exposure. No matter how well youth therapy slows it down, eventually the cumulative effect of the sun will have its effect. Sun exposure will also eventually lead to skin cancer; if you live long enough, you will get it. The same, for that matter, goes for other carcinogens: radiation, chemicals, and viruses. You can never avoid them altogether, and the longer you live the more exposure you will get. Hopefully, by the time youth therapy becomes a reality, they will have found a cure for cancer.
What about teeth and brains?
Teeth. After your baby teeth fall out, you get only one set. They don't grow. They just wear down with constant biting and chewing, and fall out due to decay or accidents. Will everybody over the age of (say) 150 be reduced to chewing on their gums, or getting false teeth? Or perhaps science will find a way to make new teeth grow - by cloning, maybe. Writers practically never think of that.
Brains. This is a bit more serious. In one Gary Larsen cartoon, a schoolboy puts up his hand and says, "Please, miss, may I be excused? My brain is full." But it might be true. Writers always seem to assume that the Methuselahs can go on thinking and remembering forever. But both activities require the growth and expansion of neurons (nerve cells), and the brain has only a finite capacity. Under hypnosis and other altered states people have been shown to activate memories - which can be proved to have been correct - of things they thought they had forgotten. It would appear that overlooked memories are not discarded, but simply buried, as if shelved in a folder marked, "Not obviously needed, but keep for possible future use." But what will happen after (say) 300 years? Will it simply become impossible to add anything more to the memory file? Will the brain become so cluttered that relevant information becomes difficult to access, so that thinking becomes bogged down? Or will the brain find some way to overwrite the old memories, and if so, will the new information get mixed up with what is left of the old, so that the mind malfunctions? Is it, in fact, possible for the brain to become full? It is worth considering.
There are also problems with bionics, as the next article will show.
Or go back to the Index.
"My teeth are getting old," I said. "They've been biting for the almost fifty-five years."
That got me thinking about the eternal quest for an elixir of youth, or some formula for the great extension of human life, and how the inventors of these schemes never think about teeth and brains.
First of all, so complex is the human body that it is hardly imaginable that ageing can be fought with a simple, one-off treatment, or even a simple periodic treatment. "Youth therapy", as I shall call it would have to entail a carefully managed cocktail of drugs, and possibly physical therapies, applied over the whole of one's life, and replete with a whole raft of side effects.
The causes of ageing are not known, but some hypotheses include the shortening of telomeres with each cell division, damage caused by free radicals produced by that essential poison, oxygen, the accumulation of wastes, and so forth. No doubt many factors are involved. But all of them boil down to the same truism: no system is perfect. The chemical composition of your body changes with every breath you inhale or exhale, every bite you take, and any movement you perform. Your body is like a waterfall: forever changing, and forever attempting to maintain its form. It is constantly wearing out and constantly repairing itself. But because the process is not 100% perfect, the wear and tear will eventually overtake the repair.
It is important to understand that not all non-infectious disorders are due to ageing. When wear and tear overtake repair in the joints, we call it arthritis. Youth therapy would slow it down, but obesity, long term heavy lifting, and a severe injury to the joint will all tip the scales towards arthritis; if you live long enough, it will catch up with you. Age will weaken the heart, but so will obesity, lack of exercise, smoking, and hypertension. Youth therapy may prevent hypertension under normal circumstances, but if you consume too much alcohol or salt it will catch up with you. Ageing thins the skin and leads to wrinkles, but so does sun exposure. No matter how well youth therapy slows it down, eventually the cumulative effect of the sun will have its effect. Sun exposure will also eventually lead to skin cancer; if you live long enough, you will get it. The same, for that matter, goes for other carcinogens: radiation, chemicals, and viruses. You can never avoid them altogether, and the longer you live the more exposure you will get. Hopefully, by the time youth therapy becomes a reality, they will have found a cure for cancer.
What about teeth and brains?
Teeth. After your baby teeth fall out, you get only one set. They don't grow. They just wear down with constant biting and chewing, and fall out due to decay or accidents. Will everybody over the age of (say) 150 be reduced to chewing on their gums, or getting false teeth? Or perhaps science will find a way to make new teeth grow - by cloning, maybe. Writers practically never think of that.
Brains. This is a bit more serious. In one Gary Larsen cartoon, a schoolboy puts up his hand and says, "Please, miss, may I be excused? My brain is full." But it might be true. Writers always seem to assume that the Methuselahs can go on thinking and remembering forever. But both activities require the growth and expansion of neurons (nerve cells), and the brain has only a finite capacity. Under hypnosis and other altered states people have been shown to activate memories - which can be proved to have been correct - of things they thought they had forgotten. It would appear that overlooked memories are not discarded, but simply buried, as if shelved in a folder marked, "Not obviously needed, but keep for possible future use." But what will happen after (say) 300 years? Will it simply become impossible to add anything more to the memory file? Will the brain become so cluttered that relevant information becomes difficult to access, so that thinking becomes bogged down? Or will the brain find some way to overwrite the old memories, and if so, will the new information get mixed up with what is left of the old, so that the mind malfunctions? Is it, in fact, possible for the brain to become full? It is worth considering.
There are also problems with bionics, as the next article will show.
Or go back to the Index.
Monday 4 August 2014
The Trouble with Bionics
My late uncle always used to call his cochlear implant his "bionic ear". Of course, it was not accurate. Bionics, at least as popularly presented, means artificial body parts which function better than the originals, and the person connected to them is called a "cyborg" (cybernetic organism): part human and part robot. The concept burst into public view with Martin Caldin's 1972 novel, Cyborg, and particularly with the television series based on it, The Six Million Dollar Man the following year.
The story followed Steve Austin, seriously crippled after an accident, provided with replacement robotic parts superior to his own. The details varied from the book to TV. In his television incarnation, he received a bionic eye which could both double as a telescope and see in the dark, along with two bionic legs which could run much faster than any human being, and a bionic right arm with tremendous strength.
I remember in one scene something huge - say a quarter or half a ton - came falling towards him, when he grabbed it with his bionic arm and held it in place before it hit the ground. It was at that point, for me, that the penny dropped. Sure, his bionic arm could lift it, but that arm was attached to a very human shoulder, and the shoulder to a very human spinal cord. The force of the weight would pass right down both of them, either ripping off his robotic arm, or crushing his spine. As for his bionic legs, I wonder whether they attached to the bony stumps of his femurs, or fitted into the sockets of his hips. And what about the muscles which normally attach to the leg at one end, and to the pelvis at the other? At the very least, running at high speed is going to put tremendous strain on his hip joints, and irreparably tear the muscles.
That's the trouble with bionic limbs. Everything is connected to everything else. But I suppose it is theoretically possible to make an artificial sense organ, such as an eye, superior to the original.
The next article will explain the effects of germs on invading aliens.
Or else, click here to return to the Index.
The story followed Steve Austin, seriously crippled after an accident, provided with replacement robotic parts superior to his own. The details varied from the book to TV. In his television incarnation, he received a bionic eye which could both double as a telescope and see in the dark, along with two bionic legs which could run much faster than any human being, and a bionic right arm with tremendous strength.
I remember in one scene something huge - say a quarter or half a ton - came falling towards him, when he grabbed it with his bionic arm and held it in place before it hit the ground. It was at that point, for me, that the penny dropped. Sure, his bionic arm could lift it, but that arm was attached to a very human shoulder, and the shoulder to a very human spinal cord. The force of the weight would pass right down both of them, either ripping off his robotic arm, or crushing his spine. As for his bionic legs, I wonder whether they attached to the bony stumps of his femurs, or fitted into the sockets of his hips. And what about the muscles which normally attach to the leg at one end, and to the pelvis at the other? At the very least, running at high speed is going to put tremendous strain on his hip joints, and irreparably tear the muscles.
That's the trouble with bionic limbs. Everything is connected to everything else. But I suppose it is theoretically possible to make an artificial sense organ, such as an eye, superior to the original.
The next article will explain the effects of germs on invading aliens.
Or else, click here to return to the Index.
No, Mr. Wells, Germs Would Not Stop the Martians.
Who could forget the climax of H. G. Wells' The War of the Worlds? Just when the whole of humanity lies prostrate under the destructive weapons of the Martians, the survivors emerge to discover that all the invaders are dead or dying, all at the same time, having no resistance to terrestrial germs, which they all caught simultaneously, and destroyed them all within the same time span. It makes a dramatic picture - until you start to think about it.
Germs aren't just floating around, ready to pounce on any unprotected organism. Even if the victim is immuno-compromised, the germs which attack it are only those that can thrive in that species. Germs are specific to their hosts and the body part of their hosts.
Take the malarial Plasmodium. It is injected into the blood stream by an Anopheles mosquito (any old mosquito won't do), and migrates to the liver, where it proliferates asexually before re-entering the blood stream, where it feeds on the red blood corpuscles. They burst, and then it spreads to other corpuscles. Eventually, it gets picked up by another Anopheles mosquito. That is a simplified version of its life cycle, of course. Each stage of the life cycle requires a particular environment. It can only live in the liver and the red blood cells. It cannot live in the lungs or gut, assuming it could ever get there. And it is limited to human beings and some close relatives. Inside a cow simply will not do. So how on earth (or anywhere else for that matter) could it survive in the liver of a Martian (assuming that they have livers), or a Martian's blood stream - which presumably functions differently to ours?
All right, malaria has a complicated life cycle. Let's try our favourite gut bacterium, E. coli. It lives, multiplies, and gains its nutriments in the lower bowels of warm-blooded animals, such as us. It is transmitted by water contaminated by faeces, but it cannot live in the mouth, pharynx, gullet, or stomach, although it must pass through them in order to reach the bowels.
Parasites are host-specific. Some are extremely specific. Smallpox, for example, was completely restricted to human beings. Others are more catholic in their choice of hosts. Indeed, many of our classic epidemic diseases are believed to have evolved from parasites endemic to our livestock. Both humans, cattle, and similar animals can get sleeping sickness. Pigs, ducks, and humans, among others, can suffer from influenza. However, even then there are restrictions. I have never heard of a dog catching sleeping sickness, or a reptile getting the flu. It is not just a case of their immune system repelling them; their internal environment is wrong.
And while we are on the subject, in 2011 there was a (deservedly) short-lived TV series called Terra Nova, about time travellers colonising the earth of 85 million years ago. In one episode, a colonist was found to have an enormous worm in his intestine. Impossible! No worm evolved to live inside dinosaurs could thrive inside a human being. The only diseases which colonists of other planets or other times could suffer from would be the ones they brought with them. If they were wise, they would practise a very strict quarantine.
Viruses are a special case. Probably most of you are aware that our genetic code is contained in DNA, and that it works by manufacturing proteins with the help of RNA. Viruses cannot reproduce by themselves. They consist simply of a string of DNA or RNA wrapped in a package of protein and lipid. They work by latching onto a host's cell by connecting with its chemical signature. That is why only certain hosts are possible. The virus then injects its DNA/RNA into the host cell, and the host cells manufactures the virus for it until it (the cell) bursts. But this assumes that the virus and the host possess the same genetic code - which they must, because they both evolved from the same original life form. But, as explained in my article on interplanetary hybrids, aliens will almost certainly be operating on a different genetic code.
Moral of the story: alien life forms would be immune to our infectious diseases. A human visitor to another planet would be immune to its plagues, no matter how severe. However, any wounds or constitutional diseases, like high blood pressure or arthritis, suffered by a space traveller could not be treated with any alien medications, for his physiology would be different.
On the other hand, certain writers such as John Norman and Alan Burt Akers have created planetary romances set on worlds which have been seeded with human life by more advanced aliens. If a visitor from earth were to arrive, remember what happened down here. When Europeans arrived in the Americas, their epidemic diseases swept through the native populations are reduced their numbers by up to 90% in the first century. On the other hand, when the same Europeans arrived in West Africa, the horrible endemic diseases turned the place into "the white man's grave". At the very least, the visitor should come down with diarrhoea just like modern tourists.
My next article will discuss the strange artwork involved in four-armed humanoids.
But you can return to the Index here.
Germs aren't just floating around, ready to pounce on any unprotected organism. Even if the victim is immuno-compromised, the germs which attack it are only those that can thrive in that species. Germs are specific to their hosts and the body part of their hosts.
Take the malarial Plasmodium. It is injected into the blood stream by an Anopheles mosquito (any old mosquito won't do), and migrates to the liver, where it proliferates asexually before re-entering the blood stream, where it feeds on the red blood corpuscles. They burst, and then it spreads to other corpuscles. Eventually, it gets picked up by another Anopheles mosquito. That is a simplified version of its life cycle, of course. Each stage of the life cycle requires a particular environment. It can only live in the liver and the red blood cells. It cannot live in the lungs or gut, assuming it could ever get there. And it is limited to human beings and some close relatives. Inside a cow simply will not do. So how on earth (or anywhere else for that matter) could it survive in the liver of a Martian (assuming that they have livers), or a Martian's blood stream - which presumably functions differently to ours?
All right, malaria has a complicated life cycle. Let's try our favourite gut bacterium, E. coli. It lives, multiplies, and gains its nutriments in the lower bowels of warm-blooded animals, such as us. It is transmitted by water contaminated by faeces, but it cannot live in the mouth, pharynx, gullet, or stomach, although it must pass through them in order to reach the bowels.
Parasites are host-specific. Some are extremely specific. Smallpox, for example, was completely restricted to human beings. Others are more catholic in their choice of hosts. Indeed, many of our classic epidemic diseases are believed to have evolved from parasites endemic to our livestock. Both humans, cattle, and similar animals can get sleeping sickness. Pigs, ducks, and humans, among others, can suffer from influenza. However, even then there are restrictions. I have never heard of a dog catching sleeping sickness, or a reptile getting the flu. It is not just a case of their immune system repelling them; their internal environment is wrong.
And while we are on the subject, in 2011 there was a (deservedly) short-lived TV series called Terra Nova, about time travellers colonising the earth of 85 million years ago. In one episode, a colonist was found to have an enormous worm in his intestine. Impossible! No worm evolved to live inside dinosaurs could thrive inside a human being. The only diseases which colonists of other planets or other times could suffer from would be the ones they brought with them. If they were wise, they would practise a very strict quarantine.
Viruses are a special case. Probably most of you are aware that our genetic code is contained in DNA, and that it works by manufacturing proteins with the help of RNA. Viruses cannot reproduce by themselves. They consist simply of a string of DNA or RNA wrapped in a package of protein and lipid. They work by latching onto a host's cell by connecting with its chemical signature. That is why only certain hosts are possible. The virus then injects its DNA/RNA into the host cell, and the host cells manufactures the virus for it until it (the cell) bursts. But this assumes that the virus and the host possess the same genetic code - which they must, because they both evolved from the same original life form. But, as explained in my article on interplanetary hybrids, aliens will almost certainly be operating on a different genetic code.
Moral of the story: alien life forms would be immune to our infectious diseases. A human visitor to another planet would be immune to its plagues, no matter how severe. However, any wounds or constitutional diseases, like high blood pressure or arthritis, suffered by a space traveller could not be treated with any alien medications, for his physiology would be different.
On the other hand, certain writers such as John Norman and Alan Burt Akers have created planetary romances set on worlds which have been seeded with human life by more advanced aliens. If a visitor from earth were to arrive, remember what happened down here. When Europeans arrived in the Americas, their epidemic diseases swept through the native populations are reduced their numbers by up to 90% in the first century. On the other hand, when the same Europeans arrived in West Africa, the horrible endemic diseases turned the place into "the white man's grave". At the very least, the visitor should come down with diarrhoea just like modern tourists.
My next article will discuss the strange artwork involved in four-armed humanoids.
But you can return to the Index here.
Sunday 3 August 2014
Four-Armed Bipeds
As everybody knows, the Hindu gods have multiple arms, and Edgar Rice Burroughs' Green Martians had four. But artists, all too often, are at a loss how to draw them. Indian painters are woeful at the task. The arms of their deities appear to fan out from somewhere on the back without any obvious joint or muscle attachments, and with the thorax the same length as that of a normal man. (Then again, perhaps gods are really built that way; they don't have to conform to human anatomic restrictions.) As for Burroughs' illustrators, well, artists are normally trained in basic anatomy so that they know how to depict the human body, but when it comes to imaginary humanoids, their skills fail them. Wave your eyes over this collection of illustrations. As you can see, some of them are reasonable, particularly those from the film, John Carter, but many of them depict the shoulders so close together they would get in one another's way. Others are really bad; they show a biped with two chests, one on top of the other, with what looks like space for a second set of lungs, and possibly a stomach.
So, in the interest of future illustrators, not to mention Hindus, I shall explain how such a being would be put together.
Here is a diagram of the human shoulder and rib cage. As you can see, I took it from a high quality book with thin pages, hence the text visible from the other side.
Your attention is drawn to the clavicle, or collar bone, which connects the scapula, or shoulder blade to the sternum, or breast bone. This system is derived from the pectoral girdle of the first four-legged animals which crawled out of the primeval sea, with their limbs sprawled to the side as you see in lizards today. In order to provide a firm support for the body, and to keep the forelegs in place, the pectoral girdle formed a closed circle of bones connecting the breast bone to the shoulder joint and the shoulder joint to the backbone.
Mammals have managed to evolve limbs which stand vertically rather than sprawl horizontally, and have lost the connection between the shoulder joint and the backbone. It is held in place by a sling of muscles. This need not be the case with a four-armed alien. Mammals such as horses, whose forelegs need to move only forward and backwards, have dispensed with the clavicle, but it is still required for climbing animals, to provide an anchor while they spread their arms horizontally.
A four-armed biped would very likely possess a longer rib cage. In any case, it is virtually certain that the breast bone would extend the whole length of the rib cage. (As you can see, the lower five pairs of human ribs do not connect to it.) It is possible that the rib cage would not flair as much towards the bottom as that of a human. What you would definitely have is a second shoulder blade at the bottom of the rib cage, and a second clavicle attached to the other end of the breast bone, making the whole structure very tight. That V-shape empty of ribs which appears in many of the illustrations is definitely wrong; its place should be taken by a visible lower collar bone, and a second set of pectoral muscles. Simple.
What about those multi-legged quadrupeds, described by Burroughs? The front two sets, next to the rib cage, would have shoulder blades as described, but not collar bones. The rear ones, not in proximity to the rib cage, would possess hip joints connected firmly to the backbone as a pelvic girdle, just as they are on earth. For extra strength, the front pelvic girdle might actually be connected to the rear one. The sequence in which these limbs moved would no doubt vary with the species, and particularly its length.
Burroughs said that the Green Martians' second pair of arms could also be used as legs. In fact, I suspect that a six-limbed intelligent life form would more closely resemble a centaur than a human being.
But, to a certain extent, these are evolutionary anomalies, which I shall deal with in my next article - unless you want to return to the Index.
So, in the interest of future illustrators, not to mention Hindus, I shall explain how such a being would be put together.
Your attention is drawn to the clavicle, or collar bone, which connects the scapula, or shoulder blade to the sternum, or breast bone. This system is derived from the pectoral girdle of the first four-legged animals which crawled out of the primeval sea, with their limbs sprawled to the side as you see in lizards today. In order to provide a firm support for the body, and to keep the forelegs in place, the pectoral girdle formed a closed circle of bones connecting the breast bone to the shoulder joint and the shoulder joint to the backbone.
Mammals have managed to evolve limbs which stand vertically rather than sprawl horizontally, and have lost the connection between the shoulder joint and the backbone. It is held in place by a sling of muscles. This need not be the case with a four-armed alien. Mammals such as horses, whose forelegs need to move only forward and backwards, have dispensed with the clavicle, but it is still required for climbing animals, to provide an anchor while they spread their arms horizontally.
A four-armed biped would very likely possess a longer rib cage. In any case, it is virtually certain that the breast bone would extend the whole length of the rib cage. (As you can see, the lower five pairs of human ribs do not connect to it.) It is possible that the rib cage would not flair as much towards the bottom as that of a human. What you would definitely have is a second shoulder blade at the bottom of the rib cage, and a second clavicle attached to the other end of the breast bone, making the whole structure very tight. That V-shape empty of ribs which appears in many of the illustrations is definitely wrong; its place should be taken by a visible lower collar bone, and a second set of pectoral muscles. Simple.
What about those multi-legged quadrupeds, described by Burroughs? The front two sets, next to the rib cage, would have shoulder blades as described, but not collar bones. The rear ones, not in proximity to the rib cage, would possess hip joints connected firmly to the backbone as a pelvic girdle, just as they are on earth. For extra strength, the front pelvic girdle might actually be connected to the rear one. The sequence in which these limbs moved would no doubt vary with the species, and particularly its length.
Burroughs said that the Green Martians' second pair of arms could also be used as legs. In fact, I suspect that a six-limbed intelligent life form would more closely resemble a centaur than a human being.
But, to a certain extent, these are evolutionary anomalies, which I shall deal with in my next article - unless you want to return to the Index.
Evolutionary Anomalies
A black cockatoo perches on one leg on the branch of a tree in a pine plantation. He is using his beak to rip into the pine cone held in his other foot. Inevitably, he drops some - which makes it so much easier for the plantation managers to collect the seed cones. You would think the cockatoo would find it much easier if he possessed a couple of hands with which to grasp the cone, so that he wouldn't have to balance on one leg. Alas! He belongs to a class whose forelegs have all been turned into wings, and even when those wings are useless for flying, as with an ostrich, a new set of forelegs cannot be evolved.
That is something which any science fiction writer wishing to create a plausible planetary fauna has to remember: evolution can only work with what it has to start with and, generally speaking, organs which are lost cannot be regained. The reason birds have no forelegs is because all land vertebrates, of which they are descendants, have only four legs. On the other hand, if birds possessed four legs as well as a pair of wings, you could bet your bottom dollar that all the mammals, reptiles, and amphibians would have six legs.
Not only that, but all land vertebrate limbs are based on the five-digit system. Many of them have lost some digits, but only a few, such as the giant panda, have gained a sixth - and the extra one develops differently from the others. If you examine the fossil record, you will find that the ancestors of the horse had more toes, and gradually lost them over time. If you examine the horse's embryo, you will find that it starts off with five toes and then loses them.
Have you ever wondered why whales have a horizontal tail fin while the tail fins of fish are vertical? Fish swim by lateral undulations. This method was then transferred to land vertebrates. If you watch a lizard, you will see that its legs sprawl out to the side, and it walks by swinging its body from side to side. Mammals, on the other hand, have managed to get their legs tucked in vertically under their bodies, allowing a more efficient gait. They flex their backbones vertically when they walk and run. So when they moved back to the sea, they maintained that method. Whales and dolphins undulate vertically. So do seals and otters.
Let's now examine a genuine fictional fauna. Edgar Rice Burroughs may have been a pulp writer, but his series on Barsoom (Mars) nevertheless display a brilliant creative imagination. But he committed three biological sins: (1) interplanetary hybrids, (2) two intelligent species, and now (3) evolutionary anomalies. It was a fine touch to make his animals multilegged, but it is puzzling to note that the calots and banths had ten limbs, the thoats eight, the white apes, apts, and Green Martians six, and the Red Martians who, despite laying eggs, nevertheless had breasts, possessed no more limbs that the earthly humans they resembled.
I am trying to imagine how this could come about. With little creepy-crawlies it is not so difficult. Common worms are made up of segments, and usually the segments carry an appendage. These have been lost in the common or garden earthworms, but you can still see them in marine worms. One step up the evolutionary ladder stand the arthropods: the familiar insects, spiders, scorpions, and so forth, which have their skeletons on the outside. They also consist of segments, each with their own appendage, a phenomenon easiest to see in the centipedes, millipedes, and prawns. Indeed, several segments have been squeezed together up front to produce a head, with the appendages converted into mouthparts. Creatures like this can easily vary in the number of legs, because simple genetic mechanisms exist to add or subtract segments.
It is another matter with large animals containing internal skeletons. It is hard to see how they could be segmented, and legs are far too complex to simply duplicate. Fish do possess segments of a sort; their bodies are made up of bands of muscles called myotomes. They still exist in us today. The bony stiffening between the myotomes have become ribs and vertebrae.
As you are aware, fish have a pair of fins at both the front and the rear. However, there was an ancient class of fish, now represented only by the coelacanths and lungfish, which possessed bony paddles where modern fish have fins. It was these fish which first crawled onto land, and their paddles became feet - each with five digits. This is why all land vertebrates are four-footed. I suppose it is theoretically possible that, on another world, a particularly long type of fish would have a middle pair of paddles as well, from which would evolve a whole tribe of six-legged land vertebrates. But I consider it unlikely that more than six legs would be possible.
Radiation can cause mutations. The biggest, the most visible ones, such as cleft palate and cystic fibrosis, are nearly always bad, because they result from the failure of a gene to carry out its allotted task. However, most physical and mental characteristics are the result of many genes, and most genes have multiple effects. That means that beneficial mutations are nearly always small in scope, the result of tweaking the rate of growth of a body part, or the effect of a hormone, for example. What you cannot get are what used to appear in those pulp scifi stories: an extra set of eyes, a set of horns, and such, for they would require a combination of a large number of changes in a large number of genes.
The other point to remember is that you get two sets of each gene, one from each parent. If the gene is dominant, it requires only one in order to manifest itself. If it requires two, it is recessive. Thus, the gene for albinism is recessive because it simply does nothing: it does not produce melanin. If you get a normal gene from one parent and the albinism gene from the other, you will be all right, because the single normal gene can produce enough melanin for your body. Only if you receive an albinism gene from both your parents will you suffer from albinism. That is why most damaging mutations are recessive.
It has been estimated that we all carry an average of three lethal genes. The reason why we don't die is that we possess only a single copy of each defective gene, rather than two. The reason our children don't die is that our partners in life possess three different lethal genes. Only if both parents are unlucky enough to carry the same mutation is there a chance that their children will be affected. The corollary is that even if increased radiation results in increased mutations, they will not show up for several generations, until the victims carrying the same mutation intermarry. That is why there was no increased incidence of birth defects following the atomic bomb attacks on Hiroshima and Nagasaki.
My next article will be on Man-Eating Plants. Click here, however, if you wish to return to the Index.
That is something which any science fiction writer wishing to create a plausible planetary fauna has to remember: evolution can only work with what it has to start with and, generally speaking, organs which are lost cannot be regained. The reason birds have no forelegs is because all land vertebrates, of which they are descendants, have only four legs. On the other hand, if birds possessed four legs as well as a pair of wings, you could bet your bottom dollar that all the mammals, reptiles, and amphibians would have six legs.
Not only that, but all land vertebrate limbs are based on the five-digit system. Many of them have lost some digits, but only a few, such as the giant panda, have gained a sixth - and the extra one develops differently from the others. If you examine the fossil record, you will find that the ancestors of the horse had more toes, and gradually lost them over time. If you examine the horse's embryo, you will find that it starts off with five toes and then loses them.
Have you ever wondered why whales have a horizontal tail fin while the tail fins of fish are vertical? Fish swim by lateral undulations. This method was then transferred to land vertebrates. If you watch a lizard, you will see that its legs sprawl out to the side, and it walks by swinging its body from side to side. Mammals, on the other hand, have managed to get their legs tucked in vertically under their bodies, allowing a more efficient gait. They flex their backbones vertically when they walk and run. So when they moved back to the sea, they maintained that method. Whales and dolphins undulate vertically. So do seals and otters.
Let's now examine a genuine fictional fauna. Edgar Rice Burroughs may have been a pulp writer, but his series on Barsoom (Mars) nevertheless display a brilliant creative imagination. But he committed three biological sins: (1) interplanetary hybrids, (2) two intelligent species, and now (3) evolutionary anomalies. It was a fine touch to make his animals multilegged, but it is puzzling to note that the calots and banths had ten limbs, the thoats eight, the white apes, apts, and Green Martians six, and the Red Martians who, despite laying eggs, nevertheless had breasts, possessed no more limbs that the earthly humans they resembled.
I am trying to imagine how this could come about. With little creepy-crawlies it is not so difficult. Common worms are made up of segments, and usually the segments carry an appendage. These have been lost in the common or garden earthworms, but you can still see them in marine worms. One step up the evolutionary ladder stand the arthropods: the familiar insects, spiders, scorpions, and so forth, which have their skeletons on the outside. They also consist of segments, each with their own appendage, a phenomenon easiest to see in the centipedes, millipedes, and prawns. Indeed, several segments have been squeezed together up front to produce a head, with the appendages converted into mouthparts. Creatures like this can easily vary in the number of legs, because simple genetic mechanisms exist to add or subtract segments.
It is another matter with large animals containing internal skeletons. It is hard to see how they could be segmented, and legs are far too complex to simply duplicate. Fish do possess segments of a sort; their bodies are made up of bands of muscles called myotomes. They still exist in us today. The bony stiffening between the myotomes have become ribs and vertebrae.
As you are aware, fish have a pair of fins at both the front and the rear. However, there was an ancient class of fish, now represented only by the coelacanths and lungfish, which possessed bony paddles where modern fish have fins. It was these fish which first crawled onto land, and their paddles became feet - each with five digits. This is why all land vertebrates are four-footed. I suppose it is theoretically possible that, on another world, a particularly long type of fish would have a middle pair of paddles as well, from which would evolve a whole tribe of six-legged land vertebrates. But I consider it unlikely that more than six legs would be possible.
Mutants
The 1950s and 1960s, when we lived under the threat of nuclear war, and the effects of radiation were not well known to the general public, were also the heyday of the pulp science fiction novels. The result was a lot of misleading depictions of the "mutants" resulting from such a conflict.Radiation can cause mutations. The biggest, the most visible ones, such as cleft palate and cystic fibrosis, are nearly always bad, because they result from the failure of a gene to carry out its allotted task. However, most physical and mental characteristics are the result of many genes, and most genes have multiple effects. That means that beneficial mutations are nearly always small in scope, the result of tweaking the rate of growth of a body part, or the effect of a hormone, for example. What you cannot get are what used to appear in those pulp scifi stories: an extra set of eyes, a set of horns, and such, for they would require a combination of a large number of changes in a large number of genes.
The other point to remember is that you get two sets of each gene, one from each parent. If the gene is dominant, it requires only one in order to manifest itself. If it requires two, it is recessive. Thus, the gene for albinism is recessive because it simply does nothing: it does not produce melanin. If you get a normal gene from one parent and the albinism gene from the other, you will be all right, because the single normal gene can produce enough melanin for your body. Only if you receive an albinism gene from both your parents will you suffer from albinism. That is why most damaging mutations are recessive.
It has been estimated that we all carry an average of three lethal genes. The reason why we don't die is that we possess only a single copy of each defective gene, rather than two. The reason our children don't die is that our partners in life possess three different lethal genes. Only if both parents are unlucky enough to carry the same mutation is there a chance that their children will be affected. The corollary is that even if increased radiation results in increased mutations, they will not show up for several generations, until the victims carrying the same mutation intermarry. That is why there was no increased incidence of birth defects following the atomic bomb attacks on Hiroshima and Nagasaki.
My next article will be on Man-Eating Plants. Click here, however, if you wish to return to the Index.
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