Well, the stone hatchet is certainly poised over our iconic cavemen. A recent Scientific American podcast admits as much, and without the narrator throwing a panic attack either.

Why this? Why now? And why such equinamity?

Secular materialist thinkers have as deep a desire as anyone to understand the wellsprings of human nature. But they are much more restricted in where they can look. From the very beginning of the organized "human evolution" movement, starting with Darwin's publication of The Descent of Man, they have mined random findings from evolution for deep truths about human nature.

The first try was social Darwinism. It is best remembered as an attempt to co-opt science to justify existing policies such as colonialism and ruthless exploitation of labour - policies earlier developed for reasons unrelated to evolution. Such policies fell by the wayside during the 20th century, of course, but sociobiology blossomed in the 1970s. Sociobiologists tried to show, using insect colonies as the key model, that the human behaviour that puzzled them - such as altruism toward strangers - was governed in reality by "selfish genes" that seek to replicate themselves. Sociobiology never came up with convincing explanations of puzzling human behaviour and soon became embroiled in controversies over alleged racism.

Later a broader movement emerged - evolutionary psychology (EP) - which scours the waterfront for human behaviours that can be traced to the survival strategies of our Pleistocene ancestors (1.8 million to about 10,000 years ago), that are now assumed to be encoded in our genes through natural selection. Thus our brains enact programs whose true nature we do not understand. But the evolutionary psychologist does.

This encoded behaviour can be shopping, voting, or tipping at restaurants.

It can also be: Why children don't like vegetables (nothing to do with young 'uns preference for sweet things); why hungry men prefer plump women (not just because they probably know where the kitchen is); why we have color vision (mainly to detect blushing); whywe are sexually jealous (not fear of abandonment, but "sperm competition"); why toddlers are Neanderthals (not just immature); why we don't stick to our goals (evolution gave us a kludge brain); why women prefer men with stubble (except for those who don't); why gossip is good for you (despite wrecked relationships); why moral behaviour is based on primitive disgust (not rational evaluation); why music exists (to "spot the savannah with little Pavarottis"); why art exists (to recapture that lost savannah); why art exists (to spread selfish genes); why altruism is really a form of sexual display; why altruism is really just selfishness; why a child must have a selfish motive for saving her sister's life; why right and wrong don't really make sense; why we don't eat grandma (because she might babysit the kids); why we don't (usually) hurt ourselves to hurt others; why we can't help behaving badly (it is programmed into our genes); oh, and religion is a sort of replicator or "meme" in our brains; and we believe in God because he is a supernatural cheat detector; or else we believe in God because belief is and is not adaptive at the same time; also, we believe in God because we have a genetic predisposition to communicate unverifiable information.

There is a dark side too. Our Stone Age ancestors are deputized to explain, as Sharon Begley observes in Newsweek, why we rape, kill and sleep around.

Now, if this all sounds like the kvetching and venting in the "Relationships" section of your local newspaper - shallow truths, at best, never deep ones - that point was certainly not lost on thoughtful scientists and philosophers. But they were not sure what to do. Some, like neuroscientist Vilayanur Ramachandran, tried parody, as in "Why Do Gentlemen Prefer Blondes?". But when a discipline is grounded in a speculative assumption (that behaviour that might have helped our Pleistocene ancestors survive is now embedded in our genes and therefore expressed unconsciously in our brains), the pace of speculation is hard to control, and the discipline becomes difficult to parody.

Some, like agnostic, common-sense philosophers David Stove and Jerry Fodor assailed EP's simplistic and counterintuitive assertions about human nature. Social scientists such as Steven and Hilary Rose, editors of the anthology Alas, Poor Darwin, weighed in on its counterfactual assumptions about human behavior. But most such efforts sank without a trace under the tide of popular delight in explanations that absolve bad or foolish behaviour with no need for repentance or amendment of life. And common sense objections were always met by the triumphant declaration that the current speculation was "based on the science of evolution." So, as Sharon Begley points out in Newsweek,

From its inception, evolutionary psychology had warned that behaviors that were evolutionarily advantageous 100,000 years ago (a sweet tooth, say) might be bad for survival today (causing obesity and thence infertility), so there was no point in measuring whether that trait makes people more evolutionarily fit today. Even if it doesn't, evolutionary psychologists argue, the trait might have been adaptive long ago and therefore still be our genetic legacy. An unfortunate one, perhaps, but still our legacy. Short of a time machine, the hypothesis was impossible to disprove. Game, set and match to evo psych.

But scientists and scholars were also troubled by evolutionary psychology's lack of science-based economy of explanation, conventionally called Occam's razor: One thinks, for example, of the big bazooms theory of human evolution, according to which men prefer women with big breasts because their ample bosoms make their fertility easier to ascertain. That is, not for the same reasons as those same men prefer big cars, big steaks, or full mugs of beer.

No doubt there is an evolutionary explanation for why creatures with any mental capacity, whether it is pre-programmed or self-directed, prefer "more" rather than "less." However, one must look vastly deeper into evolution than the story of our own human race, to discover the origin of so very general a preference among life forms. Too often, as in this case, EP appeared to be searching for something to explain rather than shedding light on human behaviour.

But the key problem with EP only became apparent after neuroscientists and other thinkers had digested a key lesson from the Decade of the Brain in the 1990s. The brain does not consist of a series of linked modules; it is a restless sea in a semisolid state, constantly reorganizing itself, according to the focus of attention provided by the mind. Adaptation to one's environment is constant and normal. Echoes from the past are just that, dimly heard echoes, not prophecies of behavior.

A new discipline, that looks much more promising for interpreting human behavior, is behavioral ecology. Behavioral ecology does not assume that a given behavior is - or ever has been - always adaptive or not adaptive. It makes predictions only for specific ecologies. For example, is it better for a girl to marry very young or wait? To marry a wealthy old man or a vigorous, young one? To marry a cousin or an outsider to the clan? Obviously, knowledge of a specific human ecology is needed before one can attempt to answer such a question. And the only thing encoded in our genes is a general capacity to apprehend and adapt to our circumstances.

As to why we rape, kill, and sleep around? Sharon Begley insists that "The fault, dear Darwin, lies not in our ancestors, but in ourselves." Or, put another way, if we create ecologies that reward a given behavior, we must deal with a lot more of it, whether we like it or not.

Denyse O'Leary is co-author of The Spiritual Brain.

Other resources

Sharon Begley offers a valuable summary of the issues. Also, an article on evolutionary psychologists' recent backpedalling.

David Brooks sums it up in the New York Times.

David Buller, once an advocate of evolutionary psychlogy, now offers serious critiques at Scientific American.

Greg Downey at Neuroanthropology weighs in against "memes" as the supposed replicators of our "selfish genes" in evolutionary psychology.

Early critic University of Chicago philosophy prof Jerry Fodor of the "common sense" school explains his misgivings here, and also here.

Robert C. Richardson, Evolutionary Psychology as Maladapted Psychology (MIT Press, 2007)