Saturday, January 17, 2009

Is Human Nature a Superstition? A Response to David Buller

Over the past twenty years, evolutionary psychology has become remarkably influential, particularly among psychologists and anthropologists. It has also won lots of journalistic coverage. Simply stated, evolutionary psychology strives to develop a Darwinian science of human nature founded on a study of the human mind as shaped by evolutionary history. The leading proponents of evolutionary psychology include Leda Cosmides, John Tooby, David Buss, Margo Wilson, Martin Daly, and Steven Pinker.

Although I have not embraced all of the ideas associated with evolutionary psychology, my appeal to a Darwinian science of human nature, including the twenty natural desires that characterize the evolved psychology of human beings, has a lot of common ground with the intellectual program of evolutionary psychology.

One of the best critics of evolutionary psychology is David Buller, a philosophy professor who is a colleague of mine at Northern Illinois University. His criticisms are laid out in his book Adapting Minds: Evolutionary Psychology and the Persistent Quest for Human Nature (MIT Press, 2005). A very brief summary of his criticisms appeared recently in SCIENTIFIC AMERICAN. The best short summary of his book is his chapter on evolutionary psychology in the third edition of Conceptual Issues in Evolutionary Biology (MIT Press, 2006), edited by Elliott Sober. Some of the reviews of Buller's book and his replies to critics can found at his home page.

Some of the proponents of evolutionary psychology have written responses to Buller. Some of these can be found at the website for the Center for Evolutionary Psychology at the University of California-Santa Barbara. One of the best responses to Buller is the essay-review by Edouard Machery and H. Clark Barrett in the journal PHILOSOPHY OF SCIENCE.

I think that in general these proponents of evolutionary psychology have persuasively answered Buller's criticisms. But I also agree with some of Buller's criticisms. I agree with him that the evolutionary psychologists sometimes stress the uniformity of human nature in such a way as to ignore the individual diversity that manifests the psychological polymorphism that has emerged from human evolutionary history. I also agree with him that in claiming that we all today have a "Stone Age mind" adapted to the environment of Pleistocene hunter-gatherers, the evolutionary psychologists mistakenly assume that there has been no human evolution over the past 10,000 years.

But on the most crucial point--the very idea of human nature--I am on the side of the evolutionary psychologists. In the last chapter of his book, Buller argues that there is no human nature, and that, as Michael Ghiselin has said, "human nature is a superstition" (419-20, 480).

If one defines human nature in a silly way (as Buller does), then human nature does not exist. But if one defines human nature in a sensible way, then human nature surely does exist.

Buller's silly definition of human nature is that it would have to consist only of traits that satisfy three conditions--first, they must be unique to human beings and thus not shared with any other animals; second, they must be invariably and exactly the same for all human individuals everywhere; and, third, they must be eternal essences that are not historically contingent.

It is easy for Buller to argue that human evolution has not produced a human species with such traits. What we take to be typically human traits are shared with other animals. These traits are highly variable across individuals because no two individuals are ever exactly the same. And as a legacy of the unending process of evolution, these traits are historically contingent in that human traits always differ across evolutionary time.

But a sensible definition of human nature does not require these conditions. We could define human nature as constituted by regularities in that suite of generally recurrent anatomical, physiological, and psychological traits that characterize the human species.

Many if not most of these traits are shared with other animals, which is exactly what one would expect from the evolution of species from ancestral species. But the fact that human beings share many traits with other mammals, for example, does not deny the importance of mammalian traits as part of the human suite of traits.

Although this suite of traits is generally recurrent across the human species, every human individual is unique, just as every animal individual is unique, and so there will be great variation across individuals. But, for example, the fact that some individuals will be born without legs does not deny the importance of a bipedal gait as part of the human suite of traits.

This species-typical suite of traits does not have to be eternal to be real for as long as it exists. The human species with its present suite of traits evolved from ancestors that did not have this suite of traits. And we can imagine that in the evolutionary future, the human species could go extinct or could evolve in some radically new direction. But the fact of evolutionary change does not deny the reality of the evolved human nature as we know it today and in recent evolutionary history. As Aristotle said in criticizing Plato's doctrine of the Ideas, "a white thing that lasts for a long time is not whiter than a white thing that lasts for a day."

Implicitly, Buller concedes the sensible definition of human nature, because he speaks of human anatomy, human physiology, and human psychology as realities that can be scientifically studied. But human anatomy, human physiology, and human psychology are all facets of human nature; and thus Buller implicitly affirms the reality of such a human nature as sensibly defined.

As Buller indicates, Cosmides and Tooby have compared their evolutionary science of psychology to the science of human anatomy. Just as one can look at Gray's Anatomy and see the anatomical adaptations that generally characterize the human species, so one should eventually be able to study human evolutionary psychology and see the psychological adaptations that generally characterize the human species. Buller speaks of this as an "analogy" between human anatomy and human nature. But, actually, it's more than an analogy, because human anatomy and human psychology are both facets of human nature, although Cosmides and Tooby choose to concentrate on the psychological facets of human nature.

Buller complains that Gray's Anatomy shows similarities among human beings "at a relatively coarse scale." But "at finer scales," human beings differ in their anatomy. No two human beings are anatomically identical. And he argues this is also true for human psychology. To speak of human psychological universals, we must "appeal to very coarse-scale common characteristics" (426).

Well, yes, but what's wrong with that? Buller says that "psychology may one day provide us with descriptions of some very widespread regularities among the minds of our conspecifics" (456). I would say that this is exactly what we mean by the psychology of human nature. Human anatomy is real, and the science of human anatomy is a real science, even though human anatomy is individually variable and a contingent product of human evolution. Likewise, human psychology is real, and the science of human psychology is a real science, even though human psychology is individually variable and a contingent product of human evolution.

So if we define human nature as constituted by "very widespread regularities" among human beings in their minds and bodies, then human nature exists. Among those "very widespread regularities," I would include the twenty natural desires that constitute the motivational basis for moral psychology. Because of the variability in those desires and in the circumstances of action across individuals and across societies, we need prudence or practical judgment in deciding what is best for particular individuals in particular circumstances. But the regularity in the human nature of those desires sets some general standards--even if "at a relatively coarse scale"--for moral thought and action.

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