Misunderstanding evolution
While I'm on the subject, this is a talk I gave a couple of years ago to secondary school students.
Some of you may think this is not so, and I am more than happy to discuss this with you after the talk, should you wish, or you can email me at the address shown there and I’ll give you some URLs and book recommendations. For now, please just take this as a statement of what modern biology implies to my mind, and leave it to another time whether you think biology is wholly mistaken about evolution, for whatever reason.
Don’t take notes – just listen. The whole talk will be available online in PDF from the website above, and it will include references too.
Why are there still monkeys?
But since we are talking about creationists and other anti-evolutionists, let’s look at one of the more common “knock-down arguments” they use against evolution:
If humans evolved from monkeys, why are there still monkeys?
Laugh if you want, but it is evidence of a deep confusion about evolutionary theory. Why indeed are there still monkeys? Why would someone think that there would not be monkeys if humans evolved from them? Now not all creationists think this is a good argument, but even so, why does it have some immediate effect on people?
The answer is simple – people think that evolution is a progressive process. Similar errors are involved in the claims that humans are the end of evolution, or that if humans went extinct, some other species would evolve to take our place as intelligent and civilised creatures. Let’s look at the errors involved. There are four:
1. That evolution moves from simple and primitive to complex and sophisticated,
2. That intelligence is somehow the goal, the most sophisticated thing, a living organism can evolve towards,
3. That when evolution occurs, the entire species changes, and
4. That if evolution were true, we would see every intermediate form that ever lived.
Each of these is not only wrong, it is in fact opposed to the scientific, Darwinian, view of evolution. The first is known by historians of ideas as the Great Chain of Being. It is an idea that goes back to the ancient Greeks, and which was especially active in the Middle Ages. John Waller, who is talking after me, will talk more about this, but it’s enough to say now that according to this pre-Darwin view, change only goes one way, while for Darwin and all who have studied biology since him, it is sometimes more useful to an organism to get simpler than to get more complex.
The second encompasses a whole range of mistakes that are usually called “teleology”, which is a fancy Greek term for “goal-centeredness”. The idea here is that there is a goal towards which things evolved, and which made them evolve. This idea is something you will find often in science fiction, particularly in the Star Trek franchise. But evolution has no goal. It does not “look ahead” and “choose” what will happen – what happens happens first, and if it works better than before, or if it is no worse than before, it might get kept. Even more important is that if it changes or stays the same, it might still become extinct.
The third is a very basic mistake, and it’s one that even famous evolutionary biologists have made, although not for a long time now. It is the idea that whole species evolve together. This means that if evolution happens, the critics think, then the older forms should disappear, but we see them (those monkeys, remember?) so therefore evolution didn’t happen. In fact, modern evolutionary biology believes (and has observed) that evolution into new species happens only in populations. In short, the ancestor of a new species isn’t an old species, but a population, or part only, of the old species. There are several mechanisms and processes for this I won’t bore you with, but if anyone is interested, I can recommend a wonderful recent book called Frogs, flies and dandelions.
So, why are there still monkeys? Because the last shared ancestor of ourselves and monkeys did not go extinct when they split off from us, because the whole species turned our way or because theirs was somehow a lesser pathway to take. Monkeys and apes do just fine in survival and reproduction terms, and that is what counts in evolution. Evolution was not heading in our direction, it got there almost by accident. And if we stopped existing, there is no reason to think there’d be a Planet of the Apes afterwards. That is, other than the planet of the apes that now exists, for we are apes, biologically speaking. But if some animal did evolve to intelligence of a human kind, I like to think it would be those meerkats – social, almost bipedal, and living in the strong selective environment of Africa, where we evolved. On the other hand, if they had any brains, and any control over their own evolution, they’d probably do better to stay pretty much the way they are…
Survival of the strongest
Natural selection is a pretty simple idea – if organisms vary in ways that are hereditable, then the better performing ones will come to dominate any population in environments that have limited resources. Seems fairly simple, right? Wrong. Not only is it not simple in the ways it works out – and it took over a century before it was mathematically understood – but many people, even quite smart people, insist on misinterpreting natural selection to mean that only the strongest survive or that competition in nature is “red in tooth and claw” as a poet in Darwin’s time had said it. An Australian philosopher well-respected for his work on the famous philosopher Hume (who influenced Darwin) wrote a book entitled Darwinian fairytales. In it, he says that if Darwin’s ideas were true, we should expect to see people and dogs fighting all the time in the street. A more complete misunderstanding of natural selection is hard to conceive.
One of the things about natural selection is that it does not involve conscious, deliberate, or active competition. Darwin himself said this, but the message got lost under the influence of another philosopher, Herbert Spencer, who insisted that a better term for Natural Selection was survival of the fittest. This naturally led people to think that “fit” here meant “stronger” or “faster”, or even just plain “meaner”. But it doesn’t. “Fit” in biology means something that seems a little odd at first. It means little more than “has the most grandchildren”. An organism is fitter than another if it ends up having more progeny over long periods of time, on average. This means that although I only have two kids of my own, I am fitter than someone who has 12 kids if my kids live to adulthood, raise many kids of their own, and so on, while theirs only end up raising a few successful grandchildren.
Evolution isn’t nice, but it is an exact bookkeeper.
Now fitness is misunderstood in another way, too. We sometimes talk about two organisms differing in fitness as if they are in every circumstance always fitter or less fit that way. This is not true. There’s a gene in countries that suffer from malaria that causes sickle cell anemia. This is a disease in which the red blood cells are misshapen, and if you have one copy of that gene from one parent, then it doesn’t make a lot of difference to you, but the malaria parasite can’t as easily infect and affect you, because it uses the red blood cells to breed in, and the sickled red blood cells are less hospitable to them. So natural selection keeps this gene at a constant frequency in those populations.
Why doesn’t it take over the populations entirely? Because if you have two copies, one from each parent, you die before you reach five. Africans and Mediterraneans whose ancestors migrated to non-malarial countries are less fit than those who don’t have these genes, and the gene is slowly being eliminated from those populations in America and elsewhere. But in malarial countries, heterozygotes, as those who have one copy of a gene are called, are fitter than those who do not carry it.
All differences in genes are like this, and so also are all differences in the form and function of the organisms those genes cause. In one place a gene can be fitter than others, while in another it can be less fit. Fitness is relative to the environment of the organism. If you doubt that, consider which bear will live more effectively if transported to the tropics – a polar bear or a black bear. And which one is fitter in the Arctic?
By the way, this is a good reason not to take seriously claims that we can “improve” the human race through breeding or genetic engineering. Unless we can foresee what environments these people will be in, and that includes what germs, pollutants, food sources, and so on, they will encounter, we just do not know if they will be fitter than their unmodified cousins.
Every day, in every way
So, what can natural selection achieve? How good can it make things? Back before Darwin there was a movement called “natural theology”, which was based on the belief that organisms were perfectly adapted to their environment. Many people think still that organisms are perfect in that way. Natural selection, rather than God’s design, is what makes them perfectly adapted, but they remain the same – ideal for what they are and do.
Only they don’t. One thing that Darwin’s view of evolution did was to draw attention to imperfection as a feature of organisms. There are lots of things that are just “bad design” – we ourselves are full of such less-than-perfection. Take the human spine, for example. We suffer from all kinds of back troubles in large part because we are trying to use in a vertical position a structure that was “designed” by evolution to bear a load when horizontal. Our remote ancestors walked on all fours – they, like we still are, were tetrapod, which means fourlegged, and at some point our ancestors shifted their mode of locomotion. And our spines haven’t yet caught up with that. Why?
Natural selection is not survival and reproduction of the best possible variation. It is only survival and reproduction of the relatively better variations in any population. If selection was a thinking agent, it would not care whether or not what beat out the competition was the best design that could be made, just whether each succeeding variation is better than the alternatives that are actually around. So if a variant happens to walk better, but suffers from back pain when it gets to my advanced age, selection is satisfied. In fact, that is what we should call it – selection is not an optimising process, it is a satisfising process (a term from Herbert Simon’s book, The Sciences of the Artificial). We really should call it survival of the more adequate. Mediocrity is OK if it’s a little bit less mediocre than whatever else is trying to make a living in the same population.
This is a general fact about similar processes in, for example, economics. Those with an abiding faith in the free market think that this will result in the best possible and most optimal outcome. But biologists know that natural selection can result in some very suboptimal situations, because selection really doesn’t look forward or care about perfection. In fact, selection can drive a population to extinction. Consider the following example:
There are two different varieties in a population of some organisms – greedy graspers and frugal misers, let us call them. The graspers get more food, more resources and will always out-compete the misers, because when there are resources, the misers get less for their children. But resources are limited and replenish at a fixed rate, say. So the graspers reduce the resources available for them to compete for. Graspers will always increase as a fraction of the population, but at the same time the population size has to reduce due to over-use of resources. Eventually, the fitter variant will drive the population extinct. In the mathematical theory of games that underpins both economic theory and evolutionary theory, this is referred to as the Tragedy of the Commons – where a common resource is used, those who use more have an edge, but overall the group loses out. And this is due to selection, both in economic markets and in ecosystems.
Another mistake therefore, is to think that natural selection works “for the benefit of the species”, as it is often put. What selection does is sort out varieties on the basis of their local efficiency at being relatively better at reproduction. If selection is for the benefit of anything, it is for the benefit of hereditable varieties; some people say that the “unit of selection” is the gene, because only genes persist over evolutionary time. This is in my view just another way of saying that traits that last for many generations do better than traits that don’t.
So we must not expect that evolution is a process that will correct our mistakes. A crucial part of evolution is what we are witnessing happen now more than any time in the history of the earth – extinction. Natural selection cannot overcome the massive challenges we are throwing at living systems if the rate at which the variants occur from which we get the “accidentally fit” mutations is less than the rate of elimination by selection in the novel environments we are creating. It is likely that evolutionary diversity will recover after we have driven most species to extinction (including ourselves in the process), but the timescale is daunting in a human perspective. It will take tens of millions of years to recover. Consider, when you think that number over – we humans are at most only 2.5 million years old, and our own species is around half a million years old. None of your descendents will see that diversity return (Wilson 1992).
Another reason why natural selection can’t achieve perfection is what we might call the You Can’t Get There From Here principle. The best example of this is a somewhat delicate subject – the vessel that transports semen in humans. In our four legged ancestors, this followed a short path from internal testicles to the penis. As the testicles evolved to be external in our lineage, and as we moved upright, the vessel, known as the vas deferens (the bit that gets the snip in a vasectomy) had to loop over the urethra, the vessel that transports urine from the kidneys. It would make a lot of sense to have the vas deferens move under the urethra, but the way it develops is based on how it developed in our ancestors, and that program can only be twisted, not recoded from the start, as it were.
So selection is neither all-powerful nor the universal acid for all problems. It is, however a sufficient explanation for the adaptation that we do see in living organisms, for those cases where there is a good fit between organisms and their environments.
Bon chance
To finish, I would like to address a mistake that predates evolution by 2000 years. It is the idea that evolution is due to chance, to randomness. Criticisms of “materialism” being based on chance and accident go back to reactions to Epicurus in Aristotle’s day. Since evolution was proposed, critics have repeatedly asserted that it is an explanation founded on chance, and so it is unscientific, against religion and the cause of all moral decay. Seriously, that is what they say.
So I want to talk a bit about chance in evolution. Darwin himself was pretty clear – for him “chance” merely meant something that we presently do not know the causes of. When genetics was developed, these “accidents” were called “mutations”, and as we have seen, mutations form the foundation of the variation on which selection acts. But chance in evolution is much more interesting than that.
Let’s get mutations out of the way first. A mutation is just a change in the genetic sequence. We know very well how they happen (and sometimes we know enough to predict where they will happen and under what circumstances); there is no sense in which we can say that chance alone acts to cause mutations. Each mutation is due to ordinary physics and chemistry acting on the molecules of genes.
More interesting is the role of chance in gene pools, in populations. Which organism mates with which is a statistical matter in populations – a population can be relatively similar all over, so that mates have a pretty well equal probability of mating with any other individual (of the opposite sex, of course!), or the population can be bunched up into subsections where mating is more likely within than between. Think of villages in a country. These probabilities affect how selection operates, because you can’t compete with someone for mating opportunities if you never meet your potential mate.
But more than this, if the population is small, then the “random mating” effect is increased. Suppose you have a dozen individuals in a very small population, one of which has a very rare gene in the larger population from which they came. That rare gene can disappear in the larger population and yet in the small one, just through random mating, it can end up dominating the resulting population that springs from these dozen. This is called genetic drift. It is worth remembering that selection is not always the explanation – often things get spread around just because a population is small, or because there is just no real selective difference in the fitness of the mutations.
But there is a sense in which new mutations are random, and this is perhaps the most interesting sense. It is the fact that since “evolution” can’t look ahead to see what is going to be needed, variations are random relative to those future needs. In fact, variation in natural evolution is random relative to the needs of organisms now. The varieties arise (through ordinary lawful physical processes) with no regard for what might be useful. What is useful is retained and spreads through the population if selection is operating, but the novelty is not caused by the need.
A critic of Darwin’s called this the contrast between “luck” and “cunning”, and many have felt intuitively that there has to be some cunning involved in evolution. So far as the biology is concerned, there isn’t – there’s no mechanism by which cunning could be employed. Although we talk about evolution as if it were an agent with intentions and the ability to calculate outcomes, in fact this is just a metaphor, a figure of speech. It’s really hard for humans not to use this figure of speech. Always bear in mind – evolution is not an agent. There really is no hidden hand behind it.
I hope that this has helped you understand evolution a bit better. There are many other misunderstandings of evolution that come up again and again, and, to be honest, most of them can be cured with a bit of exposure to the history of evolutionary thinking (Bowler 1984 – there’s a new edition in 2003). But these are the worst and most persistent.
Reading
Asterisked books are a good introduction to evolution. The double asterisked books are highly recommended.
Talk.origins Archive
*Bowler, Peter J. Evolution: The History of an Idea. Berkeley: University of California Press, 1984.
*———. Evolution: The History of an Idea. 3rd, completely rev. and expanded ed. Berkeley: University of California Press, 2003.
*Dennett, Daniel C. Darwin’s Dangerous Idea: Evolution and the Meanings of Life. New York: Simon and Schuster, 1995.
*Dawkins, Richard. The Blind Watchmaker. Harlow: Longman Scientific and Technical, 1986.
**———. Climbing Mount Improbable. New York: Norton, 1996.
*———. The Selfish Gene. New ed. Oxford UK; New York: Oxford University Press, 1989.
*Eldredge, N. Reinventing Darwin: The Great Evolutionary Debate. London UK: Weidenfeld and Nicholson, 1995.
*Gould, Stephen Jay. Life’s Grandeur: The Spread of Excellence from Plato to Darwin. London: Jonathon Cape, 1996.
*Jones, Steve. Almost Like a Whale. London: Anchor (Transworld Publishers), 2000.
**Maynard Smith, John. The Theory of Evolution. Canto ed. Cambridge; New York: Cambridge University Press, 1993.
**Patterson, Colin. Evolution. 2nd ed. Ithaca, N.Y.: Comstock Pub. Associates, 1999.
Simon, Herbert A. The Sciences of the Artificial. 3rd ed. Cambridge, Mass.: MIT Press, 1996.
**Schilthuizen, Menno. 2001. Frogs, flies, and dandelions: the making of species. Oxford: Oxford University Press.
Stove, D. C. 1995. Darwinian fairytales. Aldershot, Hants, England; Brookfield, Vt.: Avebury.
*Wilson, Edward O. 1992. The diversity of life. London: Penguin.
“Evolution is so simple, almost anyone can misunderstand it” – David HullThis talk is going to assume that evolution is a fact, that it is a fact of human biology as well as of every other organism, and that the explanations of modern biology are pretty well right.
“Nothing in biology makes sense except in the light of evolution” – Theodosius Dobzhansky
Some of you may think this is not so, and I am more than happy to discuss this with you after the talk, should you wish, or you can email me at the address shown there and I’ll give you some URLs and book recommendations. For now, please just take this as a statement of what modern biology implies to my mind, and leave it to another time whether you think biology is wholly mistaken about evolution, for whatever reason.
Don’t take notes – just listen. The whole talk will be available online in PDF from the website above, and it will include references too.
Why are there still monkeys?
But since we are talking about creationists and other anti-evolutionists, let’s look at one of the more common “knock-down arguments” they use against evolution:
If humans evolved from monkeys, why are there still monkeys?
Laugh if you want, but it is evidence of a deep confusion about evolutionary theory. Why indeed are there still monkeys? Why would someone think that there would not be monkeys if humans evolved from them? Now not all creationists think this is a good argument, but even so, why does it have some immediate effect on people?
The answer is simple – people think that evolution is a progressive process. Similar errors are involved in the claims that humans are the end of evolution, or that if humans went extinct, some other species would evolve to take our place as intelligent and civilised creatures. Let’s look at the errors involved. There are four:
1. That evolution moves from simple and primitive to complex and sophisticated,
2. That intelligence is somehow the goal, the most sophisticated thing, a living organism can evolve towards,
3. That when evolution occurs, the entire species changes, and
4. That if evolution were true, we would see every intermediate form that ever lived.
Each of these is not only wrong, it is in fact opposed to the scientific, Darwinian, view of evolution. The first is known by historians of ideas as the Great Chain of Being. It is an idea that goes back to the ancient Greeks, and which was especially active in the Middle Ages. John Waller, who is talking after me, will talk more about this, but it’s enough to say now that according to this pre-Darwin view, change only goes one way, while for Darwin and all who have studied biology since him, it is sometimes more useful to an organism to get simpler than to get more complex.
The second encompasses a whole range of mistakes that are usually called “teleology”, which is a fancy Greek term for “goal-centeredness”. The idea here is that there is a goal towards which things evolved, and which made them evolve. This idea is something you will find often in science fiction, particularly in the Star Trek franchise. But evolution has no goal. It does not “look ahead” and “choose” what will happen – what happens happens first, and if it works better than before, or if it is no worse than before, it might get kept. Even more important is that if it changes or stays the same, it might still become extinct.
The third is a very basic mistake, and it’s one that even famous evolutionary biologists have made, although not for a long time now. It is the idea that whole species evolve together. This means that if evolution happens, the critics think, then the older forms should disappear, but we see them (those monkeys, remember?) so therefore evolution didn’t happen. In fact, modern evolutionary biology believes (and has observed) that evolution into new species happens only in populations. In short, the ancestor of a new species isn’t an old species, but a population, or part only, of the old species. There are several mechanisms and processes for this I won’t bore you with, but if anyone is interested, I can recommend a wonderful recent book called Frogs, flies and dandelions.
So, why are there still monkeys? Because the last shared ancestor of ourselves and monkeys did not go extinct when they split off from us, because the whole species turned our way or because theirs was somehow a lesser pathway to take. Monkeys and apes do just fine in survival and reproduction terms, and that is what counts in evolution. Evolution was not heading in our direction, it got there almost by accident. And if we stopped existing, there is no reason to think there’d be a Planet of the Apes afterwards. That is, other than the planet of the apes that now exists, for we are apes, biologically speaking. But if some animal did evolve to intelligence of a human kind, I like to think it would be those meerkats – social, almost bipedal, and living in the strong selective environment of Africa, where we evolved. On the other hand, if they had any brains, and any control over their own evolution, they’d probably do better to stay pretty much the way they are…
Survival of the strongest
“Natural Selection is not Evolution ” – Ronald A FisherEvolution is divided into two kinds, and they get badly confused with each other. One of these is what we just talked about – speciation. The other is the process of adaptation by natural selection. The technical terms for this are cladogenesis (Greek for “the origin of branches”, of the evolutionary “tree”, that is) and anagenesis (from the Greek for “regeneration” or “change through time”).
Natural selection is a pretty simple idea – if organisms vary in ways that are hereditable, then the better performing ones will come to dominate any population in environments that have limited resources. Seems fairly simple, right? Wrong. Not only is it not simple in the ways it works out – and it took over a century before it was mathematically understood – but many people, even quite smart people, insist on misinterpreting natural selection to mean that only the strongest survive or that competition in nature is “red in tooth and claw” as a poet in Darwin’s time had said it. An Australian philosopher well-respected for his work on the famous philosopher Hume (who influenced Darwin) wrote a book entitled Darwinian fairytales. In it, he says that if Darwin’s ideas were true, we should expect to see people and dogs fighting all the time in the street. A more complete misunderstanding of natural selection is hard to conceive.
One of the things about natural selection is that it does not involve conscious, deliberate, or active competition. Darwin himself said this, but the message got lost under the influence of another philosopher, Herbert Spencer, who insisted that a better term for Natural Selection was survival of the fittest. This naturally led people to think that “fit” here meant “stronger” or “faster”, or even just plain “meaner”. But it doesn’t. “Fit” in biology means something that seems a little odd at first. It means little more than “has the most grandchildren”. An organism is fitter than another if it ends up having more progeny over long periods of time, on average. This means that although I only have two kids of my own, I am fitter than someone who has 12 kids if my kids live to adulthood, raise many kids of their own, and so on, while theirs only end up raising a few successful grandchildren.
Evolution isn’t nice, but it is an exact bookkeeper.
Now fitness is misunderstood in another way, too. We sometimes talk about two organisms differing in fitness as if they are in every circumstance always fitter or less fit that way. This is not true. There’s a gene in countries that suffer from malaria that causes sickle cell anemia. This is a disease in which the red blood cells are misshapen, and if you have one copy of that gene from one parent, then it doesn’t make a lot of difference to you, but the malaria parasite can’t as easily infect and affect you, because it uses the red blood cells to breed in, and the sickled red blood cells are less hospitable to them. So natural selection keeps this gene at a constant frequency in those populations.
Why doesn’t it take over the populations entirely? Because if you have two copies, one from each parent, you die before you reach five. Africans and Mediterraneans whose ancestors migrated to non-malarial countries are less fit than those who don’t have these genes, and the gene is slowly being eliminated from those populations in America and elsewhere. But in malarial countries, heterozygotes, as those who have one copy of a gene are called, are fitter than those who do not carry it.
All differences in genes are like this, and so also are all differences in the form and function of the organisms those genes cause. In one place a gene can be fitter than others, while in another it can be less fit. Fitness is relative to the environment of the organism. If you doubt that, consider which bear will live more effectively if transported to the tropics – a polar bear or a black bear. And which one is fitter in the Arctic?
By the way, this is a good reason not to take seriously claims that we can “improve” the human race through breeding or genetic engineering. Unless we can foresee what environments these people will be in, and that includes what germs, pollutants, food sources, and so on, they will encounter, we just do not know if they will be fitter than their unmodified cousins.
Every day, in every way
So, what can natural selection achieve? How good can it make things? Back before Darwin there was a movement called “natural theology”, which was based on the belief that organisms were perfectly adapted to their environment. Many people think still that organisms are perfect in that way. Natural selection, rather than God’s design, is what makes them perfectly adapted, but they remain the same – ideal for what they are and do.
Only they don’t. One thing that Darwin’s view of evolution did was to draw attention to imperfection as a feature of organisms. There are lots of things that are just “bad design” – we ourselves are full of such less-than-perfection. Take the human spine, for example. We suffer from all kinds of back troubles in large part because we are trying to use in a vertical position a structure that was “designed” by evolution to bear a load when horizontal. Our remote ancestors walked on all fours – they, like we still are, were tetrapod, which means fourlegged, and at some point our ancestors shifted their mode of locomotion. And our spines haven’t yet caught up with that. Why?
Natural selection is not survival and reproduction of the best possible variation. It is only survival and reproduction of the relatively better variations in any population. If selection was a thinking agent, it would not care whether or not what beat out the competition was the best design that could be made, just whether each succeeding variation is better than the alternatives that are actually around. So if a variant happens to walk better, but suffers from back pain when it gets to my advanced age, selection is satisfied. In fact, that is what we should call it – selection is not an optimising process, it is a satisfising process (a term from Herbert Simon’s book, The Sciences of the Artificial). We really should call it survival of the more adequate. Mediocrity is OK if it’s a little bit less mediocre than whatever else is trying to make a living in the same population.
This is a general fact about similar processes in, for example, economics. Those with an abiding faith in the free market think that this will result in the best possible and most optimal outcome. But biologists know that natural selection can result in some very suboptimal situations, because selection really doesn’t look forward or care about perfection. In fact, selection can drive a population to extinction. Consider the following example:
There are two different varieties in a population of some organisms – greedy graspers and frugal misers, let us call them. The graspers get more food, more resources and will always out-compete the misers, because when there are resources, the misers get less for their children. But resources are limited and replenish at a fixed rate, say. So the graspers reduce the resources available for them to compete for. Graspers will always increase as a fraction of the population, but at the same time the population size has to reduce due to over-use of resources. Eventually, the fitter variant will drive the population extinct. In the mathematical theory of games that underpins both economic theory and evolutionary theory, this is referred to as the Tragedy of the Commons – where a common resource is used, those who use more have an edge, but overall the group loses out. And this is due to selection, both in economic markets and in ecosystems.
Another mistake therefore, is to think that natural selection works “for the benefit of the species”, as it is often put. What selection does is sort out varieties on the basis of their local efficiency at being relatively better at reproduction. If selection is for the benefit of anything, it is for the benefit of hereditable varieties; some people say that the “unit of selection” is the gene, because only genes persist over evolutionary time. This is in my view just another way of saying that traits that last for many generations do better than traits that don’t.
So we must not expect that evolution is a process that will correct our mistakes. A crucial part of evolution is what we are witnessing happen now more than any time in the history of the earth – extinction. Natural selection cannot overcome the massive challenges we are throwing at living systems if the rate at which the variants occur from which we get the “accidentally fit” mutations is less than the rate of elimination by selection in the novel environments we are creating. It is likely that evolutionary diversity will recover after we have driven most species to extinction (including ourselves in the process), but the timescale is daunting in a human perspective. It will take tens of millions of years to recover. Consider, when you think that number over – we humans are at most only 2.5 million years old, and our own species is around half a million years old. None of your descendents will see that diversity return (Wilson 1992).
Another reason why natural selection can’t achieve perfection is what we might call the You Can’t Get There From Here principle. The best example of this is a somewhat delicate subject – the vessel that transports semen in humans. In our four legged ancestors, this followed a short path from internal testicles to the penis. As the testicles evolved to be external in our lineage, and as we moved upright, the vessel, known as the vas deferens (the bit that gets the snip in a vasectomy) had to loop over the urethra, the vessel that transports urine from the kidneys. It would make a lot of sense to have the vas deferens move under the urethra, but the way it develops is based on how it developed in our ancestors, and that program can only be twisted, not recoded from the start, as it were.
So selection is neither all-powerful nor the universal acid for all problems. It is, however a sufficient explanation for the adaptation that we do see in living organisms, for those cases where there is a good fit between organisms and their environments.
Bon chance
To finish, I would like to address a mistake that predates evolution by 2000 years. It is the idea that evolution is due to chance, to randomness. Criticisms of “materialism” being based on chance and accident go back to reactions to Epicurus in Aristotle’s day. Since evolution was proposed, critics have repeatedly asserted that it is an explanation founded on chance, and so it is unscientific, against religion and the cause of all moral decay. Seriously, that is what they say.
So I want to talk a bit about chance in evolution. Darwin himself was pretty clear – for him “chance” merely meant something that we presently do not know the causes of. When genetics was developed, these “accidents” were called “mutations”, and as we have seen, mutations form the foundation of the variation on which selection acts. But chance in evolution is much more interesting than that.
Let’s get mutations out of the way first. A mutation is just a change in the genetic sequence. We know very well how they happen (and sometimes we know enough to predict where they will happen and under what circumstances); there is no sense in which we can say that chance alone acts to cause mutations. Each mutation is due to ordinary physics and chemistry acting on the molecules of genes.
More interesting is the role of chance in gene pools, in populations. Which organism mates with which is a statistical matter in populations – a population can be relatively similar all over, so that mates have a pretty well equal probability of mating with any other individual (of the opposite sex, of course!), or the population can be bunched up into subsections where mating is more likely within than between. Think of villages in a country. These probabilities affect how selection operates, because you can’t compete with someone for mating opportunities if you never meet your potential mate.
But more than this, if the population is small, then the “random mating” effect is increased. Suppose you have a dozen individuals in a very small population, one of which has a very rare gene in the larger population from which they came. That rare gene can disappear in the larger population and yet in the small one, just through random mating, it can end up dominating the resulting population that springs from these dozen. This is called genetic drift. It is worth remembering that selection is not always the explanation – often things get spread around just because a population is small, or because there is just no real selective difference in the fitness of the mutations.
But there is a sense in which new mutations are random, and this is perhaps the most interesting sense. It is the fact that since “evolution” can’t look ahead to see what is going to be needed, variations are random relative to those future needs. In fact, variation in natural evolution is random relative to the needs of organisms now. The varieties arise (through ordinary lawful physical processes) with no regard for what might be useful. What is useful is retained and spreads through the population if selection is operating, but the novelty is not caused by the need.
A critic of Darwin’s called this the contrast between “luck” and “cunning”, and many have felt intuitively that there has to be some cunning involved in evolution. So far as the biology is concerned, there isn’t – there’s no mechanism by which cunning could be employed. Although we talk about evolution as if it were an agent with intentions and the ability to calculate outcomes, in fact this is just a metaphor, a figure of speech. It’s really hard for humans not to use this figure of speech. Always bear in mind – evolution is not an agent. There really is no hidden hand behind it.
I hope that this has helped you understand evolution a bit better. There are many other misunderstandings of evolution that come up again and again, and, to be honest, most of them can be cured with a bit of exposure to the history of evolutionary thinking (Bowler 1984 – there’s a new edition in 2003). But these are the worst and most persistent.
Reading
Asterisked books are a good introduction to evolution. The double asterisked books are highly recommended.
Talk.origins Archive
*Bowler, Peter J. Evolution: The History of an Idea. Berkeley: University of California Press, 1984.
*———. Evolution: The History of an Idea. 3rd, completely rev. and expanded ed. Berkeley: University of California Press, 2003.
*Dennett, Daniel C. Darwin’s Dangerous Idea: Evolution and the Meanings of Life. New York: Simon and Schuster, 1995.
*Dawkins, Richard. The Blind Watchmaker. Harlow: Longman Scientific and Technical, 1986.
**———. Climbing Mount Improbable. New York: Norton, 1996.
*———. The Selfish Gene. New ed. Oxford UK; New York: Oxford University Press, 1989.
*Eldredge, N. Reinventing Darwin: The Great Evolutionary Debate. London UK: Weidenfeld and Nicholson, 1995.
*Gould, Stephen Jay. Life’s Grandeur: The Spread of Excellence from Plato to Darwin. London: Jonathon Cape, 1996.
*Jones, Steve. Almost Like a Whale. London: Anchor (Transworld Publishers), 2000.
**Maynard Smith, John. The Theory of Evolution. Canto ed. Cambridge; New York: Cambridge University Press, 1993.
**Patterson, Colin. Evolution. 2nd ed. Ithaca, N.Y.: Comstock Pub. Associates, 1999.
Simon, Herbert A. The Sciences of the Artificial. 3rd ed. Cambridge, Mass.: MIT Press, 1996.
**Schilthuizen, Menno. 2001. Frogs, flies, and dandelions: the making of species. Oxford: Oxford University Press.
Stove, D. C. 1995. Darwinian fairytales. Aldershot, Hants, England; Brookfield, Vt.: Avebury.
*Wilson, Edward O. 1992. The diversity of life. London: Penguin.
posted by John S. Wilkins @ 2:50 pm
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