The Improbability Pump | The Nation


The Improbability Pump

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What's worse is that, contra F&P, evolutionary biologists have grappled for decades with the question of how to decide which evolving features of species experience natural selection and which do not. And they've devised observational, experimental and statistical ways to make this distinction. In the case of hemoglobin, the answer is obvious: selection couldn't act on color because in many animals the blood can't be seen through the skin. More important, mutant hemoglobins that have lost their ability to carry oxygen but remain red are invariably lethal.

The Greatest Show on Earth
by Richard Dawkins
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What Darwin Got Wrong
by Jerry Fodor and Massimo Piattelli-Palmarini
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About the Author

Jerry A. Coyne
Jerry A. Coyne is a professor of ecology and evolution at the University of Chicago. His latest book is Why Evolution...

Here's a more realistic example. Perhaps the most famous case of natural selection in action is the color change that occurred in Britain's "peppered moth" over the past 150 years. Before the Industrial Revolution, these moths had white wings speckled lightly with black, although avid collectors found a few all-black mutants. As pollution from manufacturing increased the concentration of suspended particles in the air, black moths became more numerous, and eventually predominated in many places. When clean air laws reduced Britain's pollution in the 1950s, the evolution of wing color reversed, and in most places the white color once again became common. The difference between white and black moths was shown to reside at a single gene.

What caused these evolutionary changes? There were several theories. One was that the target of selection wasn't the moth's color but the survival of caterpillars that, while not showing the color differences of adults, happened to be affected by the same gene. Another suggestion was that natural selection acted on color: perhaps sharp-sighted birds picked off moths whose color contrasted with that of the trees on which they rested. In unpolluted woods, lichen-covered trees are light-colored but turned black as pollution increased. This would give a selective advantage first to the dark-colored moths and then, as pollution abated, to light-colored moths.

F&P would presumably counsel us to give up at this point, since we can't, they say, distinguish between the counterfactuals of selection "for" larval survival and "for" adult color. But we can! Breeding experiments in the laboratory showed that the survival of caterpillars couldn't explain the increase and subsequent decline of the black form. In contrast, field experiments that involved observing predation on dead moths of different colors fastened to trees of different colors, and on live moths of different colors released in unpolluted woods, showed that selection on color was strong, easily able to explain the evolutionary changes observed in nature.

And we now have dozens of similar studies--in fish, birds, insects and plants--all successfully distinguishing those traits experiencing natural selection from those that are "free riders." Sadly, F&P show no awareness of this literature, which is hardly obscure, since it includes some of the famous cases, like the peppered moth, that we use to teach evolution to undergraduates.

Of course, in many cases we'll never know exactly which features experienced direct natural selection or how that selection worked. We can't return to the Jurassic, for instance, and find out why the stegosaurus had those big plates on its back. Were they radiators for regulating body temperature? Did they fend off predators? Or were they only a byproduct of some other adaptive change in the skeleton? Our inability to understand all the details, though, is hardly a reason to claim that natural selection doesn't work.

So if natural selection played at best a trivial role in evolution, what do F&P offer as an alternative explanation for the marvelous adaptations of plants and animals? Nothing. They finally admit that "we don't know what the mechanism of evolution is. As far as we can make out, nobody knows exactly how phenotypes evolve. We think that, quite possibly, they evolve in lots of different ways." After much demurring, they float the idea that "organisms 'catch' their phenotypes from their ecologies in something like the way that they catch their colds from their ecologies." Although this "explanation" links evolution to ecology, it's completely meaningless. How did ancestral whales catch their flukes and flippers from the water? How did ancestral birds catch their wings from the air? F&P don't say.

I've pondered long and hard how two thoughtful intellectuals could go so wrong. Behind much of F&P's animus toward natural selection, it seems, is their disdain for evolutionary psychology, which sees much of modern human behavior as the product of natural selection acting on our ancestors. (What Darwin Got Wrong includes an appendix of quotations from evolutionary psychologists, whom F&P label "unabashed adaptationists.") Here F&P have a point, for while much of evolutionary psychology is interesting, worthwhile science, it includes a speculative fringe (especially inviting to journalists) that proposes fanciful stories about how natural selection could produce behaviors like music-making, rape, clinical depression and even religion.

Fodor has long been an extreme rationalist who believes the mind is a logic machine and that the orderliness of our world must be deducible a priori from elegant laws. It's no surprise, then, that F&P produce a long diatribe against B.F. Skinner's behaviorism, the theory that animals (including humans) initially behave randomly and then repeat those behaviors that get rewarded. In its randomness, messiness and contingency, behaviorism resembles natural selection. And F&P are clearly infuriated by evolutionary psychologists' use of natural selection to explain not only human behavior but the human mind.

But evolutionary psychology is a red herring here. F&P are surely entitled to criticize evolutionary psychology, and evolutionary psychologists may be expected to reply. Motivations aside, F&P's attempt to undermine evolutionary biology is a quixotic and misguided undertaking. Their claim to have nullified 150 years of science, and one of humanity's proudest intellectual achievements, with some verbal legerdemain, is not only breathtakingly arrogant but willfully ignorant of modern biology. In the end, F&P's contrarian efforts are all belied by the world of Richard Dawkins--the flourishing field of modern evolutionary biology, where natural selection remains the only explanation for the wondrous adaptive complexity of organisms.




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