Dawkins and Gould describe the history of life on Earth in very different ways.
We continue our discussion of Kim Sterelny’s Dawkins vs. Gould: Survival of the Fittest by focusing on the disagreements between the two scientists concerning the history of life on Earth.
Punctuated Equilibrium vs. Gradualism
Dawkins has always been clear that the cumulative effects of small selection-driven changes are what constitute evolution. The development of life on Earth, according to him, is explained by natural selection driving evolution. Large-scale changes in species are just extrapolations of lots of small-scale change. Gould, however, denies this because it doesn’t jibe with the evidence as he sees it: the physical structures of nearly all living animals are based on body plans that developed in the Cambrian era five hundred million years ago. This difference in viewpoint could be attributable to the fields in which each of the authors worked. Dawkins is an ethologist, after all, so he’s interested in the behavior of organisms. As a paleontologist, Gould approaches the matter from a perspective that reflects body structure and long-term patterns and not just the pressures on the immediate population.
The fact that most species simply appear in the fossil record fully-formed, and remain basically unchanged throughout their existence, is persuasive evidence that strict gradualism doesn’t explain either the rate or the nature of species evolution. Punctuated equilibrium was the model of evolutionary change that Gould and Niles Eldredge formed in response to these challenges, and gradualists like Dawkins either dismissed the idea or made it seem like it was stating the obvious.
The other advantage that Gould has over Dawkins as a paleontologist is that he analyzes a lot of extinct species and speculates on how extinctions, particularly mass extinctions, have made the course of evolution seem more like a series of upheavals than a smooth and gradual development. Sterelny agrees that simply extrapolating local processes can’t give us a valid picture of natural history:
In the case of the dinosaurs, perhaps the meteorite only administered the final blow to a group on the way out. But I do not think that this can be in general true of mass extinction. The changes they impose are too vast. That is particularly true of the catastrophe that struck life at the end of the Permian. Probably more than 90% of animal species then alive went extinct. Extinction on this scale must have caused fundamental reorganizations of life. If so, we cannot understand the overall history of life by projecting, onto the largest scale, processes we see operating in local populations. Mass extinctions are not just local bad news scaled up.
Moreover, Gould, drawing on the work of David Raup, argues that there is a distinctive evolutionary regime in operation in periods of mass extinction. These are not casinos ruled by chance alone. There are principles which would enable us to pick winners and losers. The game has rules. But they are different rules from those of normal times. The magnitude of the upheaval at the Permian/Triassic boundary, and the pace of the upheaval at the Cretaceous/Tertiary (if the impact was important), make it unlikely that the game was fair. Adaptation, we recall, is adaptation to a specific environment. Scramble the environment—drop a polar bear in the desert—and even a species superbly adapted to its previous environment will be in very deep trouble. So, as Raup puts it, extinction was probably ‘wanton.’ Species survival is not random, but the properties on which survival depends are not adaptations to the danger mass extinction threatens. If a meteor impact caused a nuclear winter, then the ability to lie dormant would have improved your chances. But dormancy is not an adaptation to the danger of meteor impacts.
The Meritocracy of NatureDawkins’s emphasis on the non-random aspect of evolution serves a political purpose, because we consider competition a positive thing in Western society; not for nothing has “survival of the fittest” come to represent the core truth of evolution in our market-oriented culture. Gould has always remained skeptical of applying Darwinian theory to social and cultural phenomena. His constant battle against sociobiology and evolutionary psychology is motivated as much by his disdain for systems that blame natural processes for social inequities as his scorn for reductionism.
Contingency vs. Convergence
A fundamental disagreement between Dawkins and Gould about natural history is whether, if life had to develop all over again on Earth, it would come out the same way. Gould considers the development of life on Earth a process characterized by contingency, subject to stochastic elements that make a repeat unlikely. Paleontologist Simon Conway Morris took issue with Gould’s thinking, pointing to convergent evolution as evidence that evolution can be characterized as predictable up to a point. Dawkins took Morris’s side, saying he shared Morris’s “enthusiasm for convergence” even if he found some of the paleontologist’s rhetoric quasi-religious. Not surprisingly, Sterelny notes, the jury is still out:
Conway Morris, in Crucibles of Creation, argues that evolutionary convergence shows that history cannot be as contingent as Gould supposes. In convergence, two independent lineages come to resemble one another when both face similar environmental pressures. Old- and new-world vultures, for example, are not closely related birds, but they are very much alike in terms of appearance and behavior.
But there are problems with this line of thought. First, most examples of convergence are not independent evolutionary experiments. For they concern lineages with an enormous amount of shared history, and hence shared development potential. This is true of the standard example of convergent streamlining in marine reptiles, sharks, pelagic bony fish like the tune, and dolphins. Second, the scale is not large enough. The fact that eyes have often evolved does not show that had, say, the earliest chordates succumbed to a bit of bad luck (and become extinct), then vertebrate-like organisms would have evolved again. Third, Gould’s main concern is not with adaptive complexes (the source of Conway Morris’s examples) but with body plans—basic ways of assembling organisms.
I think we have to score Gould’s contingency claims as ‘Don’t know; and at this stage don’t know how to find out.’
Even though they agree that Darwin was right and evolution is an ongoing, natural process, Dawkins and Gould disagree on many fundamental issues concerning natural history. Can life on Earth be explained as a series of gradual increases in fitness adding up eventually to the dizzyingly complex biosphere we see today? Or are other forces and patterns necessary to understand natural history?