Rereading the Fossil Record: The Growth of Paleobiology as an Evolutionary Discipline

July 26, 2012

Most palaeontologists now take it for granted that our subject has significant things to say about the nature of evolutionary change; uniquely, we have the time dimension. Yet the fossil record is undeniably incomplete, and until quite recently, a prevailing view - among population geneticists, for example - was that palaeontologists had little to offer. As the evolutionary biologist John Maynard Smith put it, they should "go away and find another fossil, and not bother the grown-ups".

Not so many biologists hold such views now. There is a good reason for it, almost entirely due to the labours of a small but exceptionally vigorous group of US palaeontologists for some 15 years during the 1970s and 1980s. The whole concept of palaeontology changed dramatically, and a separate discipline, palaeobiology, was born, with its own journal: Paleobiology. Palaeontology may, or may not, have a seat at the "high table" of evolutionary biology (if there is such a thing). But this group did an extraordinary job of trying to get there.

This splendid book tells a fascinating tale; here we find the gentlemanly Norman Newell, the young tigers Niles Eldredge and Stephen Jay Gould, the brilliant, prickly Tom Schopf, the innovative David Raup, the late Jack Sepkoski (father of the author), Steven Stanley, James Valentine and many other extraordinary personalities. We read of their insights, interactions, disagreements, quarrels, personal lives and contributions. Sadly, not a few died before their time. The critical figure among them was the late Gould, but they all needed each other, despite quarrelling.

So what were the basic concepts of palaeobiology? Effectively, it made palaeontology less descriptive and more theoretical, invoked computer modelling and quantitative analysis of the fossil record, brought in biological evolutionary concepts and emphasised the evolutionary implications of the fossil record. None of this would have been possible without new technology; namely, modern high-speed computers.

A critical question was whether the patterns of change seen in the fossil record are real. Eldredge and Gould proposed "punctuated equilibria" in 1972 - in other words, rather than even and slow transformation of populations, there was rapid origin of new types, in small populations, followed by longer periods of stasis. On the other hand, Schopf was convinced that most evolutionary change was stochastic - largely random, uninfluenced by external causes. His computer-generated "spindle" models closely matched patterns seen in nature, and he never abandoned this idea. Gould, meanwhile, believed (rightly in my view) in determinism by natural selection.

Raup generated computer models of coiled mollusc shells, of which only a fraction of possible forms are used in nature. Extinctions came to be seen as highly important drivers of evolution, resetting the scenario each time. By the 1980s, five major mass extinctions had been recognised, with causes identified. Jack Sepkoski's ideas of three successive "evolutionary faunas", originating, evolving and becoming extinct together, gained wide acceptance. So did Stanley's concept that evolution above the species level was decoupled from species selection. Other ideas, such as a 26-million-year periodicity in extinctions, flourished briefly before dying.

Our perspective on the fossil record and its value for evolution changed immensely as a result of this work. Palaeontology is now much more biological, although still firmly rooted in the fossil record. We recognise that evolution is hierarchical, with genes, organisms, populations, species and genera representing different levels, and these are (or may be) operating independently. The new synthesis is not anti-Darwinian, as has been claimed. Rather, to quote David Sepkoski: "Modern evolution theory is remarkable for the continuing validity of Darwin's original insights, and also for its adaptability." That is the take-home message, and it is absolutely true.

Rereading the Fossil Record: The Growth of Paleobiology as an Evolutionary Discipline

By David Sepkoski. University of Chicago Press. 440pp, £35.50. ISBN 9780226748559. Published 28 May 2012

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