I’m finally getting around to reading Massismo Pigliucci and Jonathan Kaplan’s Making Sense ofEvolution – the Conceptual Foundation of Evolutionary Biology (University of Chicago Press, 2006). A critical argument that they make in this book, it seems to me, is that the available techniques for testing adaptive hypotheses can either not be applied to humans or can be done so only with difficulty. An important and fairly intuitive outcome of this is that we don’t have well founded evolutionary arguments for some fairly obvious human evolutionary trends: bipedalism, braininess, and relative hairlessness.
Instead of well tested insights about the evolution of key human characteristics we have a swarm of speculations, the problem with which is not that they are unconvincing but rather that they are all so seemingly plausible and we do not have a way of arbitrating them.
So how, typically, are adaptive hypotheses tested? Pigliucci and Kaplan (P+K) describe six techniques: phenotypic manipulation, transplant studies, laboratory explorations, optimization analyses, phylogenetic analyses and regression analyses. The first three pose ethical problems – to put that famous Annie Dillard quote to new use: “We can leave the library then, go back to the creek lobotomized, and live on its banks as untroubled as any muskrat or reed. You first.” Thus the equivalent of, say, filing a birds beak to test an adaptation (apparently such tests make it past the ethical boards!), might be to surgically chop a brain to test a hypothesis about the evolution of that massive protuberance, though it would be less seemly to do so. In fact all sorts of clinching experiments may suggest themselves to test human evolutionary hypotheses, but few could be ethically undertaken. P + K say that the other three approaches are possible but problematic since we often know little about the selective pressures surrounding human adaptations, and the clade to which the humans belong is relatively species poor.
The target of their critique is primarily evolutionary psychology (EP) the spunky younger cousin of sociobiology (SB) which came under stout attack from Stephen Jay Gould and Richard C. Lewontin (G+L) in their famously contentious “Spandrels” paper in 1979. In short P+K are doing to EP what G+L did to SB!
I won’t say much more about it now other than to note that one’s response might be to stanch a temptation to hypothesize about the evolution of certain human traits – especially the evolution of mental characteristics where we seems to be on especially tricky ground. This is indeed what they suggest for EP's future. Focusing on less "sexy" traits, they say, "might prove to be more promising." (p153)
Alternatively one might just have at it. Since we're in the position of being unable to test many of these ideas comprehensively we might entertain ourselves with increasingly implausible speculations knowing that they are no more nor less defensible that any others. Indeed, the very tendency to speculate about human evolution may itself be an exquisite adaptation for befuddling and stymieing one’s intellectual competitors with tall tales. S/he who is the greatest evolutionary fabulist and the least concerned with the exertion that accompanies hypothesis testing might be less prone to the life's depression inducing realities. Or this trait may, of course, be a product of runaway sexual selection. What could be sexier that a marvelous yarn about one’s origins? Are those humans who construct the splashiest evolutionary fables simple the peacocks with the prettiest ass feathers?