Thursday, September 30, 2004

It’s About Russia

I just finished reading James W. Valentine’s new tome on the evolution of the big animal groups, On the Origin of Phyla. Valentine is a heavy hitter in the phylogeny business, but his book, whose title self-consciously echoes Darwin’s epochal book, doesn’t offer any similarly earthshaking insights. I think that’s a significant result in itself. Trying to work out the particulars of a process that occurred 600 million years ago is bound to be a long slog, especially since the precursors of the various groups were tiny worm-like creatures with soft bodies that leave few fossil remains. Scientists are winnowing down the available hypotheses, however, and nobody seems to see any need for explanations that involve notions beyond what is already familiar in evolutionary thinking. Indeed, the more-or-less automatic advance of molecular biology can be expected to provide more and more reliable family trees as time wears on, though as Valentine is careful to point out, interpreting the floods of data on the genetic affinities of living organisms is far from automatic and we may never precisely identify the sponge with an attitude that was the authentic metazoan Adam. The nature of the evidence may limit us to telling likely stories about our most distant ancestors, but the point is that the stories sound more likely all the time. The subject evolves. It isn’t in crisis.

In most of the sciences, books aren’t very important because the crucial developments appear in research articles. In evolutionary biology, however, books have a larger role because of the continuing challenge of putting together a vast and heterogeneous mass of evidence to draw meaningful conclusions about living things. The grand example is the Origin of Species, a masterpiece of synthesis that is still an inevitable work 145 years after its publication; but there are a number of important books by Mayr, Dobzhansky, Stanley, Grant, Gould, Simpson, Wilson, and others that are structurally similar to Origins. I don’t think physics or chemistry has a similar bibliography. There are wonderful books in these sciences, but, aside from Galileo’s Two World Systems and Newton’s Principia, they tend to be textbooks, not the primary exposition of new ideas. Valentine’s book is hardly in a league with Tempo and Mode in Evolution, let alone the original Origin; but it’s a worthwhile example of the type.

Valentine thinks that the earliest metazoans probably lived on the floor of shallow seas. I’m a benthic form, myself, a sort of intellectual brachiopod subsisting on whatever nutritious morsels lodge in my lophophore. It is hardly surprising I have a bias in favor of inductive methods. One of the larger pieces I’ve strained from reading Valentine and other such books is that most of the creativity of evolution normally occurs at the earliest stages of the emergence of a group of organisms when some lucky founder arrives in an empty geographic or ecological zone. In that absence of competition, anything works brilliantly if it works at all. Fundamental principle of evolution (and marketing): If a thing’s worth doing, it’s worth doing badly.

An evolutionary flowering doesn’t necessarily occur because an organism develops a new adaptation. Most often some Elmer Fudd of a worm lucks into a new scene and its offspring rapidly develop into a whole range of new forms, some of which include morphological novelties that could only emerge under conditions of lessened competition. When the ancestors of what would become insects diverged from the ancestor of what would become fish, there is little likelihood that the first members of the first group looked very different from the members of the second or that what differences they did have had anything to do with being like an insect or being like a fish. That probably came later. By the same logic, the fact that there are a limited number of types of animals at any taxonomic level doesn’t imply that there are only so many basic types that work. It may just be that “when some region of adaptive space is already occupied, novelties produced to reinvade that space will usually be less well adapted than are the inhabitants, and will lose out in any sorting. Thus the Cambrian radiations may have produced enough metazoan types to occupy the broad range of available marine environments, thereby foreclosing the production of additional bodyplans.”

We tend to think of the Theory of Evolution as the explanation of how new living things emerge but most evolutionary mechanisms ceaselessly work to prevent novelty. At the beginning of every new epoch, a thousand flowers bloom precisely because a disaster or some other contingency has created a temporary cessation of competition. In nature as in history, competition merely puts a high finish on conformity and routine—the perfected Brontosaurus, the New Improved Chevy, Brad Pitt.

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