Edge: THE PATTERN OF LIFE'S HISTORY

STEPHEN JAY GOULD: THE PATTERN OF LIFE'S HISTORY

George C. Williams: I have trouble understanding Gould's persistent efforts to minimize the importance of natural selection, the adaptive changes it produces, and the other things it does. It imposes costs and allows many incidental consequences to arise from the adaptive changes. These have to be related to the adaptations by straightforward cause-effect reasoning. If something happens by chance — for instance, by genetic drift — there immediately arises the question of why drift was stronger than selection in this particular instance.

It's obviously true that there's a lot of chance in evolution, at any level. It's at the higher levels that generally you have sample sizes that are smaller — in the sense that there are not as many species in a genus as there are individuals in a species. In that kind of a situation, the survival of one entity and the extinction of another is much more likely to be a chance event.

The evolutionary process works with whatever it's got. There are no fresh starts; it doesn't design anything new, it just tinkers with what's already there. It may be that what's already there plays some essential role in life, and the life of the organism may turn out incidentally to be useful for something else. If that's important, then it may be subject to modification for that role in addition to its original one. Steve has done a great job of explaining the role of chance in macroevolution and its dependence on historical legacies. There may be a few scientists out there who are as good as Steve Gould, but there are just damn few who are good as he is at writing for a great range of readers.

He, or someone, uses as an example bird wings, which are obviously locomotor appendages. There's a heron that uses its wing to shade the water it's peering into in its search for food, just as we might do with our hand. This is a good example of something perfected as one kind of adaptation happening to be incidentally useful for something else. Whether it will be modified to make it more useful, as an aid to vision, is another matter. What were originally jawbones are now functioning as ear ossicles, which we use for hearing. In this case, they've totally lost the original function and are entirely devoted to the secondary.

This bird-wing example is what Gould calls "exaptation," and it happens all the time. But there's a semantic problem, even in calling the heron's wing a wing. That structure started out as a fin, and just incidentally turned out to be useful for walking on land, and then incidentally that kind of locomotor appendage turned out to be useful for flying with. You simply have to specify your functional perspective. You can say a wing is a flight adaptation, but it's also a flight exaptation, if you are talking about its origin as something used for walking.

Daniel C. Dennett: As I look at the history of controversy surrounding evolutionary theory since Darwin, I see a recurring pattern, in which a new wave of theorists comes along, sometimes singly, sometimes in groups, and when they first show up what they think they've got is a refutation of Darwinism; they think they've killed the beast, or at least discovered a major exemption to what they view as the intolerable implications of what the beast says. As John Maynard Smith points out, the early Mendelians — the people early in this century who rediscovered Mendel — at first thought of themselves as anti-Darwinians. They thought of Mendelism as the way to nip Darwin in the bud. They didn't see that in fact it was the salvation of Darwinism. It's roughly half the modern synthesis. In his recent book Steps Towards Life, the German chemist and Nobel Laureate Manfred Eigen notes that what he has done is revolutionary, but he knows better: he titles the epilog "Darwin Is Dead; Long Live Darwin." What he acknowledges is that what he has to say is not that revolutionary after all, it's a new wrinkle. It saves Darwin for another day. Stuart Kauffman is the same way. He starts off thinking he's the ultimate anti-Darwinian and he ends up discovering that what he has is a nice improvement to some part of Darwinism.

We'd all like to be considered revolutionaries. Stephen Jay Gould fits into that category. He aspires to bring a certain sort of Darwinism to its knees. He has fought a series of revolutions against what he views as orthodox Darwinism. When the dust clears, however, they aren't revolutions at all. They've made some interesting contributions — some important contributions — but the general public doesn't see that. What it tends to see is Darwinism on its deathbed "as Stephen Jay Gould has shown us." That's just a mistake. That's a major misperception on the part of the public.

What Darwin discovered, I claim, is that evolution is ultimately an algorithmic process — a blind but amazingly effective sorting process that gradually produces all the wonders of nature. This view is reductionist only in the sense that it says there are no miracles. No skyhooks. All the lifting done by evolution over the eons has been done by nonmiraculous, local lifting devices — cranes. Steve still hankers after skyhooks. He's always on the lookout for a skyhook — a phenomenon that's inexplicable from the standpoint of what he calls ultra-Darwinism or hyper-Darwinism. Over the years, the two themes he has most often mentioned are "gradualism" and "pervasive adaptation." He sees these as tied to the idea of progress — the idea that evolution is a process that inexorably makes the world of nature globally and locally better, by some uniform measure.

Let's take these three ideas: progress, gradualism, adaptation. I don't offhand know any evolutionist who's ever put them together that way. That's a figment of Steve's imagination. But he tries to keep these three themes always together. If he accuses you of one, the other two are likely to be coming in on the next beat and the beat after that. This is unconstructive, because certainly he would agree that somebody could be, say, a gradualist and not be an adaptationist, or be an adaptationist and not believe in progress, and so forth. In fact, his attacks on all three of these are seriously misguided.

Steve is a gradualist himself; he has to be. He toyed briefly with true nongradualism — the "hopeful monsters" of saltationism. He tried it on, he tried it pretty hard, and when it didn't sell he backed off. There's nothing wrong with gradualism.

Steve, together with Richard Lewontin, wrote a classic, notorious paper on the spandrels of San Marco. It is — supposedly- -mainly an attack on "pervasive adaptation," and on the adaptationist program. It completely misfires. Adaptationism is not the bogey they make it out to be, and they don't avoid it themselves. Steve himself is an adaptationist when it suits him.

The question is, do I agree that Richard Dawkins' version of Darwinism — or John Maynard Smith's version — is impoverished? They're the archadaptationists today, and I'd have to say that the impoverishment hasn't been shown to me yet. Certainly Steve hasn't shown it to me in his writing.

Every theme in Steve's trio is good enough in its own limited way. (His more recent business about the importance of mass extinction strikes me as pretty much of a nonstarter.) But none of those themes is original with him; they've been around in evolutionary theory since Darwin. Some people have taken them seriously and some people haven't. None is revolutionary.

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