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The Triumph of Stephen Jay Gould

There is hardly a chapter in the main body of The Richness of Life that does not repay a careful reading. Of all the essays in it the one that is most important to the public understanding of science is “Measuring Heads: Paul Broca and the Heyday of Craniology,” for it deals with an issue that is so discomfiting for scientists that they avoid it when they can. Despite the myth of detached objectivity that scientists propagate, their motivations are as messy as everyone else’s. In particular, they have political, social, and personal concerns that may influence what they do, how they do it, and what they say about it. Putting aside deliberate fraud, of which we have an embarrassment of examples, the gathering of data, their statistical representation, and their interpretation offer many opportunities for unconscious bias toward conclusions that we already “knew” to be true.

In particular, scientists have repeatedly reported that whites have larger brains than blacks. Gould shows that when the preserved brain is measured before the race of its former owner is revealed, this difference disappears completely. Similarly, claims of larger heads of professionals as compared to laborers are not statistically significant because of very large variation from individual to individual. What is important about this essay is not that it reveals what we already know to be true about the existence of racism and sexism, but that it shows how any claim that something is “scientifically demonstrated” should be treated with the same skepticism that we invoke when there is any reason to think that the investigator has something to gain, either ideologically or professionally, as we do when financial gain is involved.

Gould’s interest in form and function led him to revive interest in what was for some time a neglected aspect of evolution, the change in relative size of different body parts. It was well known in the nineteenth and early twentieth centuries that during the course of evolution different parts of similar organisms changed their relative size. So, for land vertebrates, as bodies grow larger in evolution, limbs get relatively thicker, but cranial size grows larger more slowly than the rest of the body so that heads get relatively smaller.

A major change in this relation of head size to body size occurred, however, in the immediate ancestors of humans. In the human line, cranial size has grown larger more rapidly than body size so we have, compared to apes, heads too big for our bodies. On the other hand our teeth have become much smaller. In recent years this regularity of differential growth, or allometry, of body parts is sometimes neglected because of a fashion for adaptive explanations of evolutionary change. A famous example is the Irish elk, a very large deer with grotesquely enlarged antlers. It was common to explain these huge appendages as the result of natural selection favoring males with the largest antlers, who would then win out in head-on struggles with other males in the competition for females. It was further imagined that the Irish elk as a species went extinct because it was too much of a strain to carry all that weight around on their heads.

Steve Gould neatly deflated this just-so story by showing that the antlers of the very large Irish elk were exactly the size that one would expect from the general differential growth rate of body and antlers in deer. As for the Irish elk’s extinction, their more modestly antlered ancestral species also became extinct, so it is not clear why we should pick out their extravagant headgear as the cause. The important point is that it is easy to make up adaptive stories out of one’s imagination for any feature of any organism, but that there are concrete realities of growth and physiology that need to be taken account of before lapsing into unchecked fictions. A chapter in The Richness of Life, coauthored with David Pilbeam, develops this theme for human evolution.

The phenomenon of allometry is only one of a number of possible factors that need to be considered in explaining particular evolutionary changes. It is a vulgar error to reduce the explanation of all evolutionary changes to the action of natural selection. It is not only in everyday language, however, that evolution is made synonymous with the effect of the higher reproductive fitness of some forms. Within the profession of evolutionary biology during the last thirty years there has developed an overwhelming fashion for adaptive explanations of every feature of organisms. This has been encouraged by the development of theories of kin selection and group selection in which it can be shown formally that a trait may spread in a population even though it is a disadvantage to its carrier, provided that close relatives or the population as a whole may have an increased reproductive rate. This form of reasoning, easy to do in theory but extremely difficult to demonstrate convincingly in nature, has swept through evolutionary biology.

One essay, “The Spandrels of San Marco,” reprinted in The Richness of Life, has itself become the subject of a very considerable literature. It argues that there are multiple possible explanations for evolutionary change besides direct natural selection for a trait.4 Steve Gould was enamored of early Italian church architecture and familiar with spandrels—the triangular spaces between a series of arches and the straight cornices running above them. He suggested the spandrel as a metaphor for anatomical features of organisms that were not themselves adaptive, but were the architectural consequences of building another feature, just as the spandrels filling in the space surrounding a church dome are a necessary outcome of placing a circular object on a square base. As the church spandrels may then incidentally become the locus for decorations such as portraits of the four evangelists, so anatomical spandrels may be co-opted for uses that were not selected for in the first place.

Gould’s favorite example is the human chin, whose presence is an incidental consequence of the differential growth rate of two bones in the lower jaw. The dentary bone which carries the teeth elongates more slowly than the jawbone itself, so the chin juts out. In our ape-like ancestors the jawbone grows more slowly so no chin develops. Of course one can always try to invent a story about why having a chin confers more reproductive potential, but that is a parlor game, not science.

All scientists have held up before them the lives of their great predecessors who provide idealized images of what it is to be a scientist. For physicists this is Newton. In the case of evolutionists it is Darwin. For most scientists these figures, while revered, do not represent realistic models for their own careers. Devout Christians may revere saints, but they hardly expect their own eventual canonization. There are, however, unusually ambitious scientists who, while not expecting to become another Newton or Darwin, hope to show that some important element of the standard that they have inherited from their sainted predecessors is in need of correction or even rejection. After all, didn’t Einstein become famous by showing that Newtonian physics was only an approximation of a more general truth?

Steve Gould was ambitious. In the introduction to Punctuated Equilibrium he writes that “punctuated equilibrium stands for a larger and coherent set of mostly iconoclastic concerns.” While he could not hope to smash utterly the Darwinian icon, he certainly wanted to put a noticeable crack in it. There is, however, not a single model icon, copies of which sit on the desk of every evolutionary biologist, but a large number of individually modeled figurines, some made of thinner and more fragile materials than others. Gould’s model was of delicate porcelain.

Darwin’s theory can only be understood against the background of other theories of evolution with which it disagreed. The reigning pre-Darwinian evolutionary theory was the saltational one that we associate with the name of Jean-Baptiste Lamarck. In this theory some change in the environment of a species would cause all the individuals in that species to undergo a distinct change in shape or function, which was an adaptive response. This alteration would then be inherited by all the individuals in the succeeding generation so that species adaptation occurred in discrete steps. Darwin’s theory was radically different. It assumed that in every generation one or a few individuals in a species underwent small heritable changes in form or function by chance that were independent of the requirements of the environment.

Any species would then contain at any time a large amount of variation from individual to individual. If, when the environment changed, some of these random variants were more reproductively fit, individuals with those variants would have more offspring and slowly, generation by generation, in the new environment these favorable heritable variants would increase in number until they characterized the species as a whole. The picture then was of a slow and steady change in characteristics over long periods of time as a result of small inherited changes that increased in the population because, by sheer chance, they conferred slightly greater success in the struggle for existence. Unfortunately Darwin did not always stick to this picture and in later editions of the Origin allowed for the possibility of Lamarckian inheritance of acquired characteristics.

The two contrasting theories of evolution make contrasting predictions about what we ought to find in the fossil record. If Lamarck were right, then fossils should show distinct jumps separated by long periods of constancy in successive layers of rock, while ideally, if Darwin were right, there should be a slow continuous change in form in successive layers. The inconvenient truth is that although Darwin was certainly right and Lamarck wrong about the inheritance of acquired characteristics and the presence in any species of a very large number of inherited small variations, the fossil record is mainly characterized by distinct jumps in form between successive strata.

The standard reaction by paleontologists to this annoying fact is that it is a consequence of the rarity of fossilization. If most generations of most organisms never get fossilized, then what we are seeing is instantaneous snapshots taken only once in a long while, so of course we miss most of the action. What evolutionists generally ignored was that reasonably often one also found fossil series in which virtually no change had occurred. In 1972 Niles Eldredge and Steve Gould5 proposed that we should take these jumps and periods of constancy seriously and that, in fact, most changes in form occur during the relatively short time that it takes to form new species from old ones. This was neither a rebirth of Lamarckism nor a fundamental challenge to the Darwinian theory but an application to the fossil record of particular elements of the modern theory of how the more or less continuous process of evolution gives rise to distinct species. What began as a joint proposal of two fellow graduate students became, for Steve Gould, his “coordinating centerpiece.”6

Gould’s claim to iconoclasm, to a radical revision of some aspects of Darwin’s thought, rests on Darwin’s usual characterization of evolution as being marked by a “slowness and smoothness of rate” giving rise to an “insensibly graded series.” The problem with making an agreed-upon image of Darwinian evolution is that the Origin of Species is not a technical paper appearing in a modern scientific journal after having been dissected line-by-line by a panel of technical referees. It is a nineteenth-century document, in several editions, with some contradictions within and between successive versions. Most important, it was written as a refutation of the Lamarckian theory of jumps, replacing a Lamarckian image of a staircase-like sequence of levels with an equally idealized metaphor of an inclined plane. In fact, evolutionists have long recognized that neither of these metaphors fits the real process of alternating episodes with different speeds of change. The importance of the varying tempo of evolutionary change was already emphasized over sixty years ago by the famous paleontologist George Gaylord Simpson.7 The reader might best think of evolutionary change neither as a staircase nor a ramp, but as a road winding up and down through the Catskills.

The theory of punctuated equilibrium is Steve Gould’s main claim to professional fame as distinct from his prominence as a public intellectual. While acknowledging what he characterized as his fellow scientists’ legitimate disagreements with the theory, he devotes the last pages of Punctuated Equilibrium to a discussion of what he regards as purely personal sources of criticism8 :

Given the vehemence of many deprecations, combined with a weakness or absence of logical or scientific content, I must conclude that the primary motivating factor lies in simple jealousy….

What he calls “the most unkindest cut of all” is the dismissive characterization of the theory as “trivial” by two of his fellow public intellectuals, Daniel Dennett and Richard Dawkins, who, after all, have no particular claim to evolutionary expertise. Whether Dawkins is right that punctuated equilibrium is a “minor wrinkle on the surface of neo-Darwinian theory” depends, of course, on the distance from which it is viewed. From outer space even the Himalayas will appear as a minor wrinkle on the surface of the earth.

At his premature death after the recurrence of a cancer we all thought had long ago been extirpated, Steve Gould was a success. He had the public renown he craved, a professional stature in his field that was out of the ordinary, and a very long list of honors, medals, degrees, and elections. What was most extraordinary about him, however, was the unresisting ease with which he faced his own imminent extinction. Perhaps, in the end, he was satisfied.

  1. 4

    While I contributed to this paper, the metaphor of the spandrels and the development of the idea of anatomical spandrels to which the paper owes its fame were entirely Gould’s.

  2. 5

    Niles Eldredge and Stephen Jay Gould, “Punctuated Equilibria: An Alternative to Phyletic Gradualism,” in Models in Paleobiology, edited by T.J.M. Schopf (Freeman, Cooper, 1972).

  3. 6

    Punctuated Equilibrium, p. 1.

  4. 7

    George Gaylord Simpson, Tempo and Mode in Evolution (Columbia University Press, 1944).

  5. 8

    This chapter, together with the initial autobiographical appendix, “A Largely Sociological (and Fully Partisan) History of the Impact and Critique of Punctuated Equilibrium,” occupies almost one fifth of the book.

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