Niles Eldredge - The Darwin Blogs

The Darwin Blogs – May 30, 2006.

Fossil Bashing—once again.

The Sunday May 28, 2006 Op-Ed page of the New York Times carried a strange little essay by Olivia Judson of the Imperial College of London. Judson is best known as a popularizer of what I call "ultra-Darwinism"—the idea that evolution boils down to a competition among genes for representation in the next generation—à la Richard Dawkins' "selfish genes."

Her main point is that genes can tell us a lot about evolutionary history—be it of bacteria, or ourselves. This is very true. But she uses this undeniable, if not particularly newsworthy, fact to take a cheap shot at the importance of fossils. In so doing she talks the talk and walks the walk that biologists have mouthed and trod from time to time ever since genetics came into its own at the turn of the last century. Bottom line: new discoveries make old aperçus obsolete. Not so.

In the earliest days of genetics, Hugo Devries, the Dutch biologist who remarked on mutations in the evening primrose, went so far as to say that his discoveries rendered the whole of Darwinism obsolete—as now we know why organisms resemble their parents, and we can study first-hand the origin and fate of large-scale mutations and their effects on the phenotype.

The tension between paleontologists and geneticists was never better captured than in this witty paragraph by paleontologist George Gaylord Simpson—by far the most important evolutionary-minded paleontologist of the mid-20th century—a predecessor of mine at the American Museum of Natural History in New York.

In the preface to his 1944 book Tempo and Mode in Evolution, Simpson wrote:

"Not long ago paleontologists felt that a geneticist was a person who shut himself in a room, pulled down the shades, watched small flies disporting themselves in bottles, and thought that he was studying nature. A pursuit so removed from the realities of life, they said, had no significance for the true biologist. On the other hand, the geneticists said that paleontology had no further contributions to make to biology, that its only point had been the completed demonstration of the truth of evolution, and that it was a subject too purely descriptive to merit the name 'science.' The paleontologist, they believed, is like a man who undertakes to study the principles of the internal combustion engine by standing on a street corner and watching the motor cars whiz by." (Simpson, 1944, p. xv).

Judson, in her op-ed piece, says that the "traditional use of fossils—the demonstration that evolution has happened" is "antediluvian"—according to Simpson already a familiar cry of geneticists over 60 years before Judson penned her piece. So Judson's crack is itself wholly unoriginal—if not exactly antediluvian (I was one year old when Simpson published his book—and I hate to think of my self as antediluvian!).

Simpson goes on to say, though, that what happens to 100 rats in ten years under the "fixed and simple" conditions of laboratory captive life does not necessarily tell us much about what happened to a billion rats “in the course of ten million years under the fluctuating conditions of earth history."

Simpson was suggesting that repeated patterns in the history of life might tell us how core genetic processes such as mutation rate and degree; population size; natural selection—might actually work out there in the real world—and may very well NOT look like a ten year experiment with rats or fruit flies writ large over millions of years.

Here are two examples of how paleontological patterns have contributed real, substantive insight into the actual workings of the evolutionary process:

1. My 1971 work (later published with Stephen Jay Gould as "Punctuated Equilibria" in 1972—see my "Confessions of a Darwinist" downloadable from this website) stressed the formidable stability of species for many millions of years (most notably in marine invertebrates like my trilobites and Steve's snails). Stability ("stasis") is the inevitable result of the different mini-histories encountered by semi-isolated populations of far-flung species: predators, prey, diseases, climate, availability of water (for land-living animals and plants) all vary over the landscape where any one particular species lives. The chances for natural selection moving any species with a wide distribution in any one particular sustained evolutionary direction are therefore miniscule.

Stasis should have been a predicted result of population genetics by the 1930s (Sewall Wright almost got there). But instead it is an empirical result from the fossil record—and its explanation is also largely framed by paleontologists (most recently working with a consortium of geneticists and ecologists). See the paper "The Dynamics of Evolutionary Stasis" newly added to the "Niles Eldredge Library of Evolution" on this website.

2. Judson refers to extinct organisms as "also rans"—losers in the struggle for existence; by implication (an implication going straight back to Darwin, hence itself "antediluvian") that extinction is a reflection of the winners in evolution beating out the losers.

This is disingenuous at best—and given what is widely known, downright fatuous. Ecosystems are from time to time disrupted, and organisms of many species die off—to be replaced when the disturbance fades and members of peripheral surviving populations come back into the affected area to take their place. There is little or no evolutionary modification of the phenotypes of the component species—and ecosystems typically quickly regain their old look.

On the other hand, mass extinctions that have shaken life over the entire planet 5 or 6 times since the dawn of macroscopic, multicellular life have taken out entire groups of organisms—such as the trilobites at the end of the Paleozoic and the terrestrial dinosaurs at the end of the Cretaceous Periods. Once major groups are lost, others appear to take their place—either newly evolved (modern hexacorals evolved from pre-existing anemone-like ancestors only after the Paleozoic tetracorals became extinct at the end of the Paleozoic)—or, more usually, groups already present finally have a chance to dance in the evolutionary sun once the dominant groups are gone: mammals and dinosaurs evolved in mid-Triassic times. For the next 150 million years or so, mammals played subsidiary roles in Mesozoic ecosystems—until dinosaurs and collateral kin became extinct at the end of the Cretaceous—and mammals almost immediately radiated and began filling major roles in terrestrial ecosystems (and invading the air as bats and the waters as whales, pinnipeds, etc.).

The intermediate range between local ecosystems disruption and global mass extinction lies in the hundreds of regional ecosystem disturbances that were sufficiently severe to drive entire species (though not entire major groups) extinct. The fossil record shows that by far the majority of new species that have appeared on earth evolved in concert with these regional extinction spasms (these are the “turnovers” of Yale paleontologist Elisabeth Vrba). Turnovers are thus the real locus of most of evolution in the history of life. There is no way genetics has—or could ever have—predicted these results.

Stasis and extinction/speciation turnovers at various spatiotemporal scales are not just a litany of what-happened-next in evolution—rather, they are a specification of some very important general rules of how the evolutionary game is in fact played in "real-time" in the real world—all coming from paleontology. In point of fact, little shockingly new has come from genetics since its inception that causes us to change the basic Darwinian picture of evolution through natural selection. But modem genetics deeply enriches the story in many ways—and I am especially keen to learn all that is new in the striking field of evo-devo—where the progress towards understanding how genetic information is utilized in the developmental process has enormous implications for understanding the transformation of adult structures in evolutionary history.

But it is childish to slam a field you clearly do not understand in order to trumpet the importance of one's own field. If something is important, its virtues can be understood on their own merit—and not by defaming another field that if anything has done more to modify the traditional Darwinian depiction of evolutionary processes than has genetics since its inception over a century ago.

Niles Eldredge

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