University of Chicago evolutionary geneticist, Jerry Coyne, reviewing, for The Nation, Jerry Fodor and Massimo Piattelli-Palmarini’s book, What Darwin Got Wrong (2010), gives as clear a definition of natural selection as you’re ever likely to find:
In principle, natural selection is simple. It is neither a “law” nor a “mechanism.” It is, instead, a “process”–a process that is inevitable if two common conditions are met. First, some genes must harbor variation because of mutation; and second, some of those mutant genes must be better at replicating than others–usually because they improve the survival and reproduction of their carriers. Suppose, for instance, that the brown-colored ancestors of the polar bear included some carrying mutations in “pigment genes” that gave them lighter coats. These mutant bears would have an advantage: being more camouflaged in the snow than their darker confreres, they’d be able to sneak up on seals more easily and so get more to eat. Because well-fed individuals leave more offspring, over time the bear gene pool would become increasingly enriched in light-color genes. Eventually the species would evolve the familiar white polar bear coat. And this is the way, we think, that all organisms acquire that appearance of “design” that, before Darwin, was attributed to God. . . . There is no agency, no external force of nature that “acts” on individuals. There is only differential replication of genes, with the winners behaving as if they were selfish (that’s shorthand, too).
And Coyne also explains, with admirable clarity, why Jerry Fodor and Massimo Piattelli-Palmarini’s thesis that natural selection is “what Darwin got wrong” is itself wrong. Contra Jerry Fodor and Massimo Piattelli-Palmarini’s claim, for example, that we can’t really know what trait (among many) that natural selection might be acting upon in an organism, Coyne insists that, yes, indeed, we can. Evolutionary biologists have three methods for identifying where selective pressures are coming from:
[C]ontra 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 other words, Coyne insists that natural selection is neither an imprecise term, an ephemera, nor a metaphor. It is real, and scientists have “observational, experimental, and statistical ways” of finding out what, exactly, is being put under evolutionary pressure by natural selection. He offers England’s famous peppered moths as illustration, explaining why biologists know that the color of these moths is influenced by predation from birds, and not, say, larval survival:
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.
Coyne’s takedown of Jerry Fodor and Massimo Piattelli-Palmarini appears pretty damning. It’s hard to argue, after reading Coyne’s review of their book, that natural selection is on perilous intellectual ground (either experimentally or conceptually). Instead, Coyne makes a clear and compelling case that the news of natural selection’s death is greatly exaggerated.
Coyne did such an excellent job taking down Jerry Fodor and Massimo Piattelli-Palmarini, I can’t help but hope that he might do a similar number on Simon Conway Morris.
This post needs a poem. Here’s Robert Frost:
I found a dimpled spider, fat and white,
On a white heal-all, holding up a moth
Like a white piece of rigid satin cloth —
Assorted characters of death and blight
Mixed ready to begin the morning right,
Like the ingredients of a witches’ broth —
A snow-drop spider, a flower like a froth,
And dead wings carried like a paper kite.
What had that flower to do with being white,
The wayside blue and innocent heal-all?
What brought the kindred spider to that height,
Then steered the white moth thither in the night?
What but design of darkness to appall?–
If design govern in a thing so small.