Introduction by:John Brockman
Source:Edge
Natural selection is about the differential survival of coded information which has power to influence its probability of being replicated, which pretty much means genes. Coded information, which has the power to make copies of itself—“replicator”—whenever that comes into existence in the universe, it potentially could be the basis for some kind of Darwinian selection. And when that happens, you then have the opportunity for this extraordinary phenomenon which we call "life".
My conjecture is that if there is life elsewhere in the universe, it will be Darwinian life. I think there's only one way for this hyper complex phenomenon which we call "life" to arise from the laws of physics. The laws of physics—if you throw a stone up in the air, it describes a parabola, and that's it. But biology, without ever violating the laws of physics, does the most extraordinary things; it produces machines which can run, and walk, and fly, and dig, and swing through the trees, and think, and produce the whole of human technology, human art, human music. This all comes about because at some point in history, about 4 billion years ago, a replicating entity arose, not a gene as we would now see it, but something functionally equivalent to a gene, which because it had the power to replicate and the power to influence its own probability of replicating, and replicated with slight errors, gave rise to the whole of life.
If you ask me what my ambition would be, it would be that everybody would understand what an extraordinary, remarkable thing it is that they exist, in a world which would otherwise just be plain physics. The key to the process is self-replication. The key to the process is that ... let's call them "genes" because nowadays they pretty much all are genes. Genes have different probabilities of surviving. The ones that survive, because they have such high fidelity replication, are the ones which we see in the world, the ones which dominate gene pools in the world. So for me, the replicator, the gene, DNA, is absolutely key to the whole process of Darwinian natural selection. So when you ask the question, what about group selection, what about higher levels of selection, what about different levels of selection, everything comes down to gene selection. Gene selection is fundamentally what is really going on.
Originally these replicating entities would have been floating free and just replicating in the primeval soup, whatever that was. But they “discovered” a technique of ganging together into huge robot vehicles, which we call individual organisms. An individual organism is a unit of selection in a different sense from the replicator being a unit of selection. The replicator is the unit of selection which strictly is the thing that becomes either more numerous or less numerous in the world. Nowadays we say more numerous or less numerous in the gene pool, and that's modern post-Darwin language.
But because the individual organism is such a salient unit in which these replicators, these genes, have ganged up together, we as biologists tend to see the individual organism as the unit of action. The individual organism is the thing that has legs or wings, it has eyes, it has teeth, it has instincts. It's the thing that actually does something. And so it's natural for biologists to phrase their questions of purpose, of pseudo-purpose at the level of the organism. They see the organism as striving for something, working for something, struggling to achieve something.
What's it struggling to achieve? Well, for Darwin it was struggling to achieve survival and reproduction. Nowadays we would say it's struggling to achieve replication of the genes inside it. And this all comes about because, well, one way of putting it, and I've often put it like this, is to say look backwards at the ancestors of all modern animals, any animals, any time, and you can that the individual is descended from an unbroken line of successful ancestors, an unbroken line of individuals which succeeded in surviving and reproducing. What that really means is they succeeded in passing on the genes that built them. So we are conduits for the genes that pass through us. We are temporary survival machines. Everything about biology can be understood in this way. Everything about biology can be understood if you say that what's really going on is differential replicator survival—gene survival in gene pools—and the way in which they do it is by controlling phenotypes. And those phenotypes in practice are nearly all bundled up into these discrete bodies, individual organisms.
If ever there is a bundle of replicators, a bundle of genes, which passes on its genes to the next generation in a single propagule (we do that: we pass on our genes in sperms or eggs) that means that all the genes in a body, in a mammal body, in a vertebrate body, in an animal body, a normal animal with sexual reproduction. Because all the genes in that body have the identical expectation of getting into future generations, namely leaving the present body in a sperm or an egg, that means that all the genes in a body are pulling for the same end. They all have the same goal.
If they didn't (and some of them might not: viruses, for example, have a different goal of being sneezed out, or being spat out, or whatever it might be) they, of course, are quite different, and they do not cooperate with the rest of the genes in the body. But all the genes that have the same expectation of the future, the same expectation of leaving the present body and getting into the next body, they cooperate. They work together. That's why bodies are such coherent wholes. That's why all the limbs and all the sense organs work together. It's simply because all the genes that built them have the same exit route to the next generation. The minority that don't, things like viruses, they have a different exit route, and they don't cooperate, and they may kill you.
Although it's true that the great majority of survival machines are actually discrete organisms, that doesn't necessarily have to be the case, and if genes can influence phenotypes that are outside the body, then they will do so. This is the extended phenotype. The simplest sort of extended phenotype would be an artifact like a bird's nest. So a bird's nest is an organ, it's an organ in just the same sense as a heart or a kidney is an organ, but it just happens to be outside the body and it happens to be made of grass and sticks rather than being made of the cells that contain the genes. But nevertheless, it's a phenotype, which is produced by the animal's nervous system, working through nest-building behavior. And it does exactly the same kind of thing, namely preserve the genes in the form of eggs and chicks, as organs of the body, like kidneys and livers and muscles.
The next kind of extended phenotype that I talk about is hosts of parasites, because there are these spectacular examples, which Dan Dennett is fond of quoting. For example, of parasites which influence their hosts in order to get into the next host. A host body to a parasite gene is like a bird's nest. It's influenced by the genes. We don't normally put it that way. We normally say that the parasite, the fluke, or whatever it is, the whole fluke influences the whole snail to get itself passed on.
But, in fact, if you think at the genetic level, the genes are influencing the fluke's phenotype, which, in turn, influences the snail's phenotype to enhance the propagation of the fluke's genes into the next generation. So there's no reason to draw a line around the fluke's body and say, well, outside that is no longer proper phenotype. It is proper phenotype, it's just that you have to think outside the box ... in this case outside the fluke ... in order to get the true relationship between genes and phenotypes.
And then generalizing further, a cuckoo in a nest influences the behavior of its host by various stimuli, by having a bright red beak, and squawking in the right way and so on. And once again, just as the fluke influences the snail to get itself passed on to the next generation, the cuckoo influences the reed warbler to get itself, to get its genes passed on to the next generation. And the change in reed warbler behavior can properly be regarded as phenotypic expression of cuckoo genes.
My vision of life is that everything extends from replicators, which are in practice DNA molecules on this planet. The replicators reach out into the world to influence their own probability of being passed on. Mostly they don't reach further than the individual body in which they sit, but that's a matter of practice, not a matter of principle. The individual organism can be defined as that set of phenotypic products which have a single route of exit of the genes into the future. That's not true of the cuckoo/reed warbler case, but it is true of ordinary animal bodies. So the organism, the individual organism, is a deeply salient unit. It's a unit of selection in the sense that I call a "vehicle".
There are two kinds of unit of selection. The difference is a semantic one. They're both units of selection, but one is the replicator, and what it does is get itself copied. So more and more copies of itself go into the world. The other kind of unit is the vehicle. It doesn't get itself copied. What it does is work to copy the replicators which have come down to it through the generations, and which it's going to pass on to future generations. So we have this individual / replicator dichotomy. They're both units of selection, but in different senses. It's important to understand that they are different senses.
Now, because the individual organism is such a salient unit, biologists after Darwin got into the habit of seeing the organism as the unit of action, and therefore they asked the question, what is the organism maximizing? What mathematical function is the organism maximizing? Fitness is the answer. So fitness was coined as a mathematical expression of that which the organism is maximizing. Of course, what fitness really is, or what it ought to be if we understand it properly, is gene survival. For a long time fitness was equated in people's minds with reproduction, with having a large number of children, grandchildren, great-grandchildren. Bill Hamilton and others, but mostly Bill Hamilton, realized that you had to generalize that because, if what's really going on is working to pass on genes, offspring, grandchildren, et cetera, are not the only ways of passing on genes. An organism can work to enhance the survival and reproduction of its siblings, its nephews, its nieces, its cousins and so on. Hamilton worked out the mathematics of that.
I think it was unfortunate that Hamilton, having realized this very important insight, chose to stick with the individual organism as the entity of action. He therefore coined the phrase "inclusive fitness", as the mathematical function which an individual organism will maximize if what it's really doing is maximizing its gene survival. It's a rather complicated thing to calculate. It's difficult to calculate in practice and this has led to a certain amount of, not hostility, but a certain amount of skepticism about inclusive fitness as a measure, skepticism which I share. But for me the remedy of that skepticism is to say, well, forget about the organism and concentrate on the gene itself. Ask yourself (as Hamilton also did) ask yourself, if I were a gene, what would I do to maximize my propagation into the future? Hamilton did that, but he also, I think, later took a sort of false trail (it's strictly correct but not helpful) by saying if I'm an individual, what would I do to maximize my gene survival? Both ways of phrasing it are correct, they're both correct if you can get the calculation right, but one of them is rather harder to do. If you're trying to do intuitive Darwinism, if you're trying to work out what would you expect to happen in the world, I think it's better to ask the question, what would I do if I were a gene, rather than what would I do if I were an elephant?
In both cases this is a personification. Nobody really thinks that either genes or elephants scratch their heads and think, what would I do; but it's a useful trick, a useful dodge when you're trying to get the right answer as a field biologist in the Serengeti. It's a useful trick to say what would I do if I was a ... and you could fill in the end of that sentence by saying either if I was a gene or if I was an elephant. And you'll get the right answer if in the gene case you concentrate on self-replication and if in the elephant case, you concentrate on passing on genes. So we have these two logically equivalent ways of expressing what's going on in Darwinism. Both of them Hamilton used. There is the what-would-I-do-if-I-was-the-gene way of doing it, and there's the what-would-I-do-if-I-was-an-elephant-or-an-aardvark way of doing it and they're both correct. I think some of the opposition to Hamilton, which has recently surfaced, is because people have realized that inclusive fitness is not a very practical way of doing things. It's a difficult thing to calculate. And my suggestion would be (and I actually said this to Hamilton) my suggestion would be to abandon inclusive fitness and to concentrate instead on personification of the gene and then you'll get the right answer.
George C. Williams in 1966 wrote a brilliant book, Adaptation and Natural Selection, roughly at the same time as Hamilton was working, and they both tumbled to the same truth, which is that what's really going on in natural selection is survival of genes. Williams was eloquent on this. Williams said things like, Socrates may have had any number of children, we don't know that, but what Socrates really passed on, if he passed on anything, was genes. It's genes that pass through the generations. And so whenever you're talking about teleonomy, whenever you're talking about the pseudo-purpose, which is what we see in life, what's it for, what's the adaptation for, who benefits, cui bono, whenever you ask that question you should be looking at the level of the gene. Williams realized that, Hamilton realized that.
In The Blind Watchmaker, I wanted to get across the idea that cumulative selection can give rise to immense complexity and dramatic changes. So I wrote a computer program for the Macintosh, which presented on the screen a range of phenotypes which were built by an algorithm which I called its embryology, which was actually a tree-growing algorithm. And the shape of the tree was governed by genes. There were nine genes I think in the first version, and so what the user saw on the screen was a "parent", as I called them, in the middle, and eight [actually fourteen, misremembered as eight in the interview] other biomorphs around it were the offspring. They were built by genes which were nine numbers. The genes could mutate by either having a small amount added to their value or a small amount subtracted from their value. So all the nine biomorphs looked a bit different, were obviously descended from the same parent, but they were a little bit different. And you could choose with a mouse which one to breed from, it glided to the center of the screen, produced fourteen offspring and so on. It went on and on through generation after generation. You could breed anything you like. It was a most extraordinary experience to breed massively different shapes from the original by gradual degrees, and they came out looking like insects, and flowers and all sorts of things.
I'm pleased to note that although I’d thought I’d lost these biomorphs, because modern Macs don’t run the software that old Macs do ... a wonderful man called Alan Canon in Kentucky wrote to me and said he wanted to revive them. So I sent him all my old Pascal code, which would no longer run, and he’s now hard at work producing phoenix from the ashes—my old programs—and I’m simply delighted by this.
I then went to the Artificial Life Conference, organized by Chris Langton, and I gave a talk called "The Evolution of Evolvability", which I think was the first time the phrase had ever been used, and it's being used quite a lot.
The original biomorph program had nine genes. I then later enlarged it to 16 genes. I added genes that did things like segmentation, that had biomorphs that were arranged serially along the body like a centipede which has lots of different segments, or like a lobster which has lots of segments, but each segment can be a little bit different. I had genes that had symmetries of various kinds. So I increased the number of genes from nine to sixteen and the repertoire of biomorphs that became possible to breed then dramatically increased. It was still limited, but nevertheless it increased. And it occurred to me that this was a good metaphor for radical changes in embryology that happened at certain important times in evolution. For example, I just mentioned segmentation. The very first segmented animal had some kind of major mutation, which gave it two segments instead of one, I'm guessing. It may have been three. It can't have had just one and a half segments. There must have been at least two. It duplicated everything about the body. If you look at the body of an earthworm or a centipede, it's like a train, like a truck. Each truck is similar to the neighboring trucks and may be identical.
Before the origin of segmentation in the ancestors of earthworms, or the ancestors of centipedes, the ancestors of vertebrates, animals must have evolved as just one single segment, and they would have evolved in the same sort of way as my biomorphs did when they had only nine genes. Then the first segmented animal was born. It must have been radically different from its parents. This must have been a major mutation. And as soon as the first segmented animal was born with two segments, the same as each other, probably ... it wasn't a difficult thing to do in one sense because all the embryological machinery to make one segment was already there. And so to double it would have been obviously a major step. Nevertheless, all the machinery is there. It's not like inventing a whole new organ, like an eye. That cannot happen. It's got to happen by gradual cumulative selection, which is the main message of The Blind Watchmaker. But once you've got the machinery to make an eye, or to make a vertebra, or to make a heart or anything like that, you could make two because the machinery is already there. That's what segmentation is.
And so when segmentation was invented by some kind of macro mutation, a whole new flowering of evolution became possible and vertebrates, arthropods, annelids, all exploit this new embryological trick of segmentation. And I illustrated this with my biomorphs because when I added the segmentation gene for the macro mutation, which I actually had to program in, when I added it, it meant that a whole new flowering of morphology could appear on the screen. You could evolve much more exciting animals because segmentation was there. Similarly with the genes for symmetry. I had genes doing kind of mirror image morphology in two different planes. And immediately I started being able to breed things like flowers, butterflies, beautiful creatures.
The evolution of evolvability, then, is an evolutionary change which makes a radical alteration in embryology, and that opens up floodgates of further evolution which were not possible before. Segmentation is one example, sex may be another one. Torsion in mollusks may be another one. These are major changes, which I think are rare. They may happen once every 100 million years, but there's kind of normal evolution which goes on by the normal cumulative, slow, gradual process that we mostly teach about. But every now and again I suspect there's a major jump, a macro mutation which opens up new floodgates, and segmentation would be the best example. I was really led to think about this by the addition of seven more genes to my original nine gene biomorph, and that's what I talked about at Chris Langton's Artificial Life Conference, and I called it "The Evolution of Evolvability".
I incorporated these ideas of evolution evolvability in Climbing Mount Improbable, which is a bit similar to The Blind Watchmaker, but has a lot more in it. And by then I'd added a whole lot more genes, in this case introducing colors, and we now have color biomorphs. And perhaps rather more interestingly, I teamed up with Ted Kaehler. He was one of Apple's star programmers. I met him at the Artificial Life Conference. And after that we collaborated on a new project which I called "Arthromorphs", which was somewhat similar to biomorphs, but with a totally different kind of embryology, and much more based upon segmentation, and much more based upon especially arthropod segmentation. And the arthromorph program didn't require the programmer, namely me, to introduce the new watershed changes, the new macro mutations which led to new flowerings of evolution. It happened internally, it happened in the computer. They really were macro mutations. That was a big step in my use of computers in both understanding and teaching about evolution.
~~
One of the things that I've always done is not make a clear
separation between books that are aimed at popularizing, books that are
aimed at explaining things to other people, and books that explain
things to myself, or explain things to my scientific colleagues. I think
the separation between doing science and popularizing science has been
overdone. And I have found that the exercise of explaining to other
people, which I suppose I've been fairly successful at, is greatly
helped by the fact that I first have to explain it to myself. And
explaining it to myself ... the biomorph program, which I originally
wrote to explain to students, and I used them in student practicals ...
led me to think anew for myself, stimulated me to understand much better
about evolution, stimulated me to understand about the evolution of
evolvability in a way that I haven't before.
~~
Nobody knows whether there's life elsewhere in the universe. I think
there probably is. The number of stars in the universe is something
like 1022, and most of them have probably got planets. It
would be pretty astonishing if we were unique. It would go against the
lessons of history, you know, we're not the center of the universe, et
cetera. Science fiction writers try to speculate about what life
elsewhere might be like. I have one contribution to make, which is that I
think however weird, and alien, and strange, and different life
elsewhere might be, we can say one thing about it, which is that it will
be, if we discover it, it will turn out to be Darwinian life.I think there's only one way for the lead of pure physics to be transmuted into the gold of complex life, and that is differential replicator survival, which is Darwinism in its most general sense. So I would stick my neck out and say that when and if we ever discover life elsewhere in the universe, it will be Darwinian, it will be based upon something like DNA, probably not DNA, but something like DNA in the sense of an ultra-high fidelity, self-replicating coding system with the capability of producing great variety, which is what DNA does. So what I call universal Darwinism is the doctrine, almost, the one thing we know about life everywhere, is that it's Darwinian life.
I gave a talk called "Universal Darwinism" at one of the Darwin Centenary Conferences, the one in Cambridge, and I based it upon looking at all the alternatives that someone might have suggested like Lamarckism, inheritance of acquired characteristics, the principle of use and disuse. The point I tried to make is that contrary to what most biologists have said, the thing that's wrong with Lamarckism is not just that it doesn't work in practice, that acquired characteristics are not as a matter of fact inherited. There are biologists, including Ernst Mayr who have said Lamarck's theory is a fine theory, but unfortunately acquired characteristics are not inherited. The point I made was that even if they were inherited, the Lamarckian theory is nothing like a big enough theory to do the job of producing complex adaptations. Lamarckian theory depends upon use and disuse. The more we use our muscles, the bigger they get. That's fine, that happens, and then inheritance of acquired characteristics, you pass on your bigger muscles to your children. Ernst Mayr said that's a perfectly good theory. The only trouble is it doesn't work because acquired characteristics are not inherited, which of course, is true.
But the point I was making was that even if it was true, the principle wouldn't work to produce real interesting biological evolution. Muscles are fine, that's one thing that does grow bigger when you use them. But something like an eye, the delicate focusing mechanism of the eye, the transparency of the eye, the huge number of light-sensitive cells, three different color coding and so on, that doesn't come about by use and disuse. The more you use your eyes, they don't become more (the lens doesn't become more transparent as photons wash through it. The eyes become better because every single tiny mutation that improves the eye. As Darwin said, nature is daily and hourly scrutinizing. So every little tiny change, no matter how deeply buried in internal cellular biochemistry it is, if it has any effect whatever on survival and reproduction, natural selection will pick it up. The Lamarckian principle will work only for very, very crude growth, things like muscles getting bigger when you use them.
As we look around the world in which we live, what we see is stupefyingly complicated manmade machines like this camera that you're filming with, this recording machine, this computer, cars, ships, planes. These are not produced directly by natural selection, these are produced by human ingenuity, by human brains working together. No one human can make a Boeing 747. I mean, this is a cooperative enterprise involving lots of humans, involving lots of computers. It's a fantastic extension of the Darwinian substrate. So the principles that give rise to the very strong design of a plane, or a car, or a computer, these all come from human brains. But that's not the ultimate explanation. The human brains themselves have to come from Darwinian natural selection. So if we go to other planets and discover extremely complicated technology, that technology itself will be the direct product of Darwinian selection, but it will be the product, ultimately, of Darwinian selection of the brains ... whatever they call them on that planet. It's arguable that something ... this is a different kind of argument now ... it's arguable that something like Darwinism does go on in human technology: that when a human designer is designing on the drawing board, he designs something, doesn't like it, tosses it in the bin, gets a fresh bit of paper, designs a slight variation of it and so on. There might be a Darwinian element to that. That's not what I'm saying.
I'm saying that a wholly new, at least partly new, kind of design came into the world when human brains started to exercise ingenuity, especially social ingenuity, cultural ingenuity. But the ultimate source of that is evolved brains, and the evolved brains have to come about by some version of Darwinian selection, which on other planets might be very different, but it will still be, I conjecture, I bet my shirt on it being Darwinian.
No comments:
Post a Comment