|Perhaps music serves as a mating display or a means of coordinating social interactions. Maybe religiosity serves as a group-level adaptation, allowing some to persevere over others. Some researchers, known generally as evolutionary psychologists, seek rigorous ways to investigate such complex human traits. In so doing, they're pushing the boundaries of scientific explanation and addressing aspects of human behavior once believed to be off-limits for scientists.
As a field, evolutionary psychology (EP) has the difficult, and some say untenable, mission of discerning whether complex human qualities--everything from sexual attraction to language--are adaptations honed through natural selection or just nonadaptive byproducts of a uniquely human collection of cognitive systems.
Born roughly 30 years ago from the study of adaptation and altruism by George Williams, W.D. Hamilton, Robert Trivers, Edward O. Wilson, and others, as well as from advances in cognitive science, primatology, and hunter-gatherer studies, EP gained further recognition with 1992's The Adapted Mind,1 an anthology that explored culture's evolutionary foundations, including language, parental care, environmental aesthetics, and sex. Wilson, now a Harvard professor emeritus, identified the field in the 1975 book, Sociobiology.2 He defines EP as "the study of the biological basis of all forms of social behavior in human beings." He suggests that scientists dispense with the name sociobiology and call it EP, to skirt criticisms that the field championed racism and genetic determinism.
EP, though gaining acceptance, remains divisive. Proponents and practitioners face the challenge of empirically and methodologically using evolutionary history and rationale to decipher the motivations behind distinct human behaviors--to show how they might be adaptations hard-wired in the human brain.
KIPLING'S UNINTENDED LEGACY Twenty-five years ago, paleontologist Stephen Jay Gould and biologist Richard Lewontin3 criticized the so-called adaptationist program, charging that overeager biologists labeled some organisms' traits adaptations without real evidence. Many traits, they said, were actually byproducts, associated with adaptations, but not the result of natural selection. The bridge of one's nose will hold up one's glasses, but it's not an adaptation for such.
This so-called science, argued Gould and Lewontin, boiled down to little more than just-so stories--referring to Rudyard Kipling's century-old children's fables that offered imaginative explanations for certain animals' distinctive qualities.
"That was just a foolish paper," says Wilson. "All scientists deal in hypotheses and in scenarios. That's how they formulate and identify the problem that they hope to solve. [Gould and Lewontin] confused hypothesis formation with what they thought was just empty story-telling."
But as evolutionary psychologists address more complex cultural features, justly or unjustly, they haven't escaped the just-so criticism. Nevertheless, the field has become more accepted. Hires of evolutionary psychologists at psychology and anthropology departments are more common, says psychology professor Martin Daly, McMaster University, Hamilton, Ontario, editor-in-chief of the journal Evolution and Human Behavior, a major forum for EP studies.
SHOOTING BLANKS "What we're after is mapping the properties of universal human nature," explains John Tooby, codirector of the Center of Evolutionary Psychology at the University of California, Santa Barbara, and coeditor of The Adapted Mind. Humans, suggests Tooby, have a variety of specialized evolved systems for handling the social and environmental challenges faced by their hominid ancestors. For instance, Tooby and colleagues propose that humans have a selected-for "kin recognition system" adaptation, which is linked to an "incest avoidance subsystem" and disposes persons to like and care about those unconsciously identified as their genetic kin. Tooby hypothesizes a "kinship estimator" that calculates kinship based on how long two individuals lived together in childhood, patterns of nursing, and other cues that would have accurately identified genetic kin. Such an estimator would help avoid the deleterious effects of incest and promote the beneficial effects of familial cooperation.
The evolutionary psychologist's role, explains Tooby, is to identify byproducts and adaptations. He has explicitly contested the notion that the brain is a blank slate, shaped almost entirely by learning, an extreme position labeled the Standard Social Science Model (SSSM). Rather, he says, natural selection parses the brain into behavior-specific modules. But David Sloan Wilson, a professor of evolutionary biology at Binghamton University in New York, worries that this "narrow school" of EP has become too polarized. "It turns EP into a counterweight rather than a theory of the whole mind," he says.
Regardless, whether or not the field can yet claim any significant advances in scientists' study of human behavior is still debatable. Even some practitioners aren't certain how fruitful EP will be. "Except for very few things, mostly to do with sex and violence, there haven't been really any cognitive breakthroughs that are the result of evolutionary psychology," says Scott Atran, senior research scientist at the National Center for Scientific Research in Paris.
Atran, however, calls it a wonderful enterprise with opportunities to generate potentially fruitful hypotheses. But like Darwin's theory when first presented, most of EP, says Atran, currently entails consistency arguments: plausible but unproven rationales. It remains to be seen, he argues, whether EP will blossom into a fecund area of study like Darwin's work or go the way of phrenology.
MURDER, MUSIC, AND MASS APPEAL The field does have some obvious inherent methodological drawbacks. Focusing on the human as the primary object of study is both a blessing and a curse. Investigators can communicate with their subjects like no other; but resulting data often can be misleading. People are biased and have imperfect self-knowledge, says Daly.
He contends that the field has gotten better at zeroing in on the factors underlying people's judgments. The key, suggests University of Texas evolutionary psychologist David Buss, is to use multiple methods, including observations, physiological recordings, and comparisons with demographic data. Buss is studying the evolution of homicidal tendencies. He's asked normal subjects about the frequency, duration, and nature of any homicidal thoughts they've experienced, but he's also looked at police reports and eyewitness testimonies of 350 known killers. Using imaging technologies to isolate brain functions related to EP hypotheses is also becoming increasingly prevalent.
EP is no more speculative, argue proponents, than any branch of psychology. Indeed, EP may be less speculative since it incorporates evolutionary constraints. One important means of improving the field, says Marc Hauser, codirector of the Mind, Brain and Behavior program at Harvard, is to incorporate comparative animal data, particularly primate cognition data, something that hasn't been particularly commonplace in a human-centric field.
Limits exist as to what can be approached scientifically, says Steven Pinker, Harvard psychology professor and author of The Blank Slate,4 a treatise against SSSM thinking. In the case of music, for example, no one has successfully shown why, based on computer simulation, mathematical model, or physical analysis, listening to rhythmic and tonal patterns should bring about some effect on human reproduction. "In my mind, there's nothing to test for because there's no coherent theory in the first place," Pinker says.
But Hauser and others are tackling the topic. His lab studies consonant versus dissonant music in monkeys versus humans. They discovered that while human subjects preferred harmonious rather than unpleasant sounds, the animals were indifferent. Now, the question: Did a perceptual bias for linking sound structures with emotions evolve uniquely in our species or in other animals as well? "It begins to open the door and point out a method so that you can begin to ask that question," says Hauser, whose group also studies the evolutionary origins of language, mathematics, and morality.
Regarding the evolutionary significance of religious behavior, David Sloan Wilson, in Darwin's Cathedral,5 argues that based on extensive historical data, religion is actually a group-level adaptation. In the case of Calvinism, for instance, followers formed an adaptive unit that persevered better than some other groups, factions, or individuals. Atran has a different view. Religious behavior, he writes in his book In Gods We Trust,6 is not an adaptation per se, but a byproduct. Religiosity results from a group of innate psychological faculties, each of which has evolved to help deal with existential human dilemmas like death, pain, and loneliness.
The scope of EP will likely become clearer as the field continues to grow. "There's a lot of fashion to evolutionary psychology," says Atran. "A lot of people are getting into this because they think it's easy science. And the result is there's so much nonsense. My fear is that it's turning off some of the really good scientists."
Others take inconsistencies in the field in stride. "There's no question there's crap in the field," says Hauser. "But there's crap in a lot of fields."
Eugene Russo (firstname.lastname@example.org) is a freelance writer in Takoma Park, Md.
1. J. Barklow et al., The Adapted Mind: Evolutionary Psychology and the Generation of Culture, New York: Oxford University Press, 1992.
2. E.O. Wilson, Sociobiology: The New Synthesis, Cambridge, Mass.: Belknap Press, 1975.
3. S.J. Gould, R.C. Lewontin, "The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme," Proc R Soc Lond B Biol Sci, 205:581-98, 1979.
4. S. Pinker, The Blank Slate: The Modern Denial of Human Nature, New York: Viking, 2002.
5. D.S. Wilson, Darwin's Cathedral: Evolution, Religion, and the Nature of Society, Chicago: University of Chicago Press, 2002.
6. S. Atran, In Gods We Trust: The Evolutionary Landscape of Religion, New York: Oxford University Press, 2002.