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Fallen Angels

Wonderful Life: The Burgess Shale and the Nature of History

by Stephen Jay Gould
Norton, 347 pp., $19.95

I was once asked to be the commentator at a Philosophy of Science Association meeting on a paper by a famous epistemologist on the difference between theory confirmation in physics and in evolutionary biology. At first I was worried that I would not understand his paper, but after I read it, what worried me was that I did understand it.

Biology has been an embarrassment to the philosophers of science and so, for a very long time, most of them pretended it did not exist, or denied that it was real science at all. The great guru of modern philosophy of science, Sir Karl Popper, declared in The Poverty of Historicism that despite the claim of its practitioners to be scientists, the theory of evolution is not a science at all, but what he elsewhere called a “metaphysical research program.” He has since changed his view to some extent, but the unease that the study of biology creates in the hands of an older generation of philosophers remains. During the last twenty years the philosophy of science has become more and more, in the hands of a younger generation of philosophers egged on by a few of their more insightful elders like Marjorie Grene, the philosophy of biology. The historical irony is that with cries of “No Poppery!” they have nearly all chosen to study evolutionary biology.

At the heart of the philosophers’ preference for physics over biology is the question of uncertainty. Science is supposed to be a study of what is true everywhere and for all times. The phenomena of science are taken to be reliably repeatable rather than historically contingent. After all, if something happens only on occasional Tuesdays and Thursdays, popping up when one least expects it like a letter from the IRS, it is not Science but History. So, philosophers of science have been fascinated with the fact that elephants and mice would fall at the same rate if dropped from the Tower of Pisa, but not much interested in how elephants and mice got to be such different sizes in the first place. In terms of the formal calculus of propositions, the statements of science are supposed to be so-called “universally quantified” statements of the form—

For all x, if x is A then x is B

—rather than historical statements, which are only existentially quantified—

There exists an x such that x is B.

The point, Popper tells us, is that the first kind of statement can always be falsified, by finding a single example that does not obey the rule, while we can never disprove the second kind because we may have accidentally missed the cases that agree with it. So the first kind of statement is what characterizes a science, while the second kind is just storytelling.

Philosophers have not been alone in claiming that science must be about universals. In a fit of severe physics envy, biologists, even evolutionary biologists concerned with the history of life on earth, have tried to construct their science as a set of universal “laws,” acceding to the general intellectual disdain for the merely particular. Beginning with Darwin’s notion that there is a universal “struggle for existence” that is the engine of evolutionary history, through R.A. Fisher’s “Fundamental Theorem of Natural Selection” of 1930 that claimed (over-optimistically, as it turned out) to be an equation for making general predictions, to the presentday assertion that virtually all DNA evolves at a constant clock-like rate, evolutionists seeking fame and fortune have invented their own versions of the law of gravity. Wonderful Life is Stephen Gould’s powerful reassertion of the importance of historical contingency in evolutionary explanations. As its subtitle suggests, it is not the history of nature that is at issue in Gould’s book since that is the concern of all evolutionary biology; the question is whether that history is the necessary unfolding of universal laws of life, whether the race is to the swift, the battle to the strong, and riches to the wise, or whether, as Gould argues, time and chance happeneth to all. In the process, Gould shows again that he is unique among evolutionists in the subtlety and depth of his thinking about the history of life.

To understand the problem of historical contingency in evolution, we must distinguish between two kinds of statements, both of which appear at first sight to be universal assertions. Consider two favorites of philosophers:

All planets move in ellipses


All swans are white.

The first of these is truly universal because it applies not only to all planets that actually exist but to all planets that could conceivably exist, because the shape of planetary orbits is a necessary consequence of the relations of the motions of objects in a gravitational field. All physicists are agreed upon this, and that is why philosophers of science have so loved physics.

On the other hand, the assertion that all swans are white. Some biologists would say that if all swans are white, it is because the laws of development or the exigencies of natural selection make it impossible, in principle, for black swans to exist. In this respect, swans are like planets and biology is like physics. Other evolutionists would say that “swans” is simply the name of a finite collection of historical objects that may happen all to be white, but not of necessity. The black ones have just not come along yet, but could perfectly well do so at any time.1 Finally, we might simply say, “If it isn’t white, it isn’t a swan,” and leave the matter as a purely taxonomic one. While the last ploy may seem a mere trick, it plays an important role in the story of the Burgess Shale, although Gould barely mentions it in his book.

The history of evolutionary theory has been the history of the struggle among these various views of swans. On one side are arch-adaptationists who see every pimple on the body physical and the body politic as a necessary consequence of natural selection, leading to optimal adaptation of the organism to the problems of life. For adaptationists, human intelligence, social organization, and control of external nature were inevitable consequences of long-term natural selection forces and could have been foresee by an intelligent Martian watching terestrial evolution from afar. The argument is that natural selection favors those characteristics that increase the average rate of offspring production, and so eventually, traits that maximize flexibility and the ability to manipulate nature will appear. Influential works such as E.O. Wilson’s Sociobiology and Richard Dawkins’s The Selfish Gene are hautes vulgarisations of this major determinist tradition on evolutionary theory. According to Gould, this element in evolutionary explanation has grown in the last half century, in a “hardening of the evolutionary synthesis,” to become the dominant mode, replacing an earlier, more pluralistic theory.

The problem with the determinist view of evolutionary necessity is that it does not tell us why all animals (and plants, for that matter) are not as intelligent and well organized socially as we are. Bad luck? But then there are important contingencies in evolution, and swans do not have to be white after all. Curiously, over the half century during which Gould sees the evolutionary synthesis as being “hardened” around optimizing natural selection, there has been a proliferation of technical literature of alternative explanations that do not depend on direct natural selection for traits. They all emphasize historical contingency.

First, real populations of organisms are finite, and as a consequence no generation is a precise statistical copy of its parental generation. Variable traits fluctuate in frequency from generation to generation and eventually one or another form comes to characterize the species by sheer chance. In the literature of probability theory, this is known as the “drunkard’s walk,” by analogy with the drunk who emerges from the bar in the middle of the block and who staggers randomly left and right until he falls off the curb at one end of the block or the other.

A second consequence of the finiteness of population size is that most newly arisen mutations are lost to the species within a few generations, even mutations that are favored by natural selection. Had we but world enough and time, the favorable mutations would arise again and again until finally one took hold. But no species lives forever. More than 99.99 percent of all species that have ever existed are already extinct, and the average length of life of a genus of carnivores had been only about ten million years, a fraction of 1 percent of the history of life.

Third, there is more than one way to skin a cat. Identical selective forces do not lead to identical ends but depend on the actual genetic state of the species when selection begins. It is a well-known property, even of “deterministic” physical systems, that one cannot predict where a system will end up if one does not know where it started. The day before I started to write this article, I traveled eighty-five miles west, then seventeen miles north, and then again eight miles west, but from that information alone, you cannot guess that I wrote it in Marlboro, Vermont. So it is probable that one and two-horned rhinoceroses exist, not because it is better to have one horn in India and two in Tanzania and Sumatra, but because the same force of natural selection produced different solutions to the same problem, beginning with somewhat different genetic materials in the three parental species.

Fourth, genes that influence traits are organized on physical bodies, the chromosomes, that tend to be inherited as a single unit, so that different genes do not have independent fates in inheritance. If natural selection favors a particular trait and increases the incidence of genes that influence the trait, other genes that are by chance mutation on the same chromosome will also be increased despite their total irrelevance to the selective forces. This “genetic hitchhiking” results in chance selection of a trait without selection for it.

All of these phenomena, and the list is not exhaustive, point to the role of chance and contingency in the outcome of evolutionary processes, even when the deterministic force of natural selection is operating. It follows that if evolution could be run all over again from the beginning, a completely different set of organisms would arise. We do not know of totally rejected evolutionary experiments, which is what made Karl Popper despair of evolution as a science, but we occasionally get glimpses of long-extinct assemblages of organisms that appear to be very different from any others that we know. Evolution occasionally gets off on a different track, and as with God’s failed attempt to produce a lasting set of angels the first time around, there is a general housecleaning. The Burgess Shale is a rock formation that contains a record of these fallen angels and provides the ammunition for Gould’s struggle with the determinist forces.

  1. 1

    There are in fact black swans in Australia, which is why philosophers use this particular example, but we will pretend that Australia is still Terra Incognita.

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