March 14, 2000
Human Nature: Born or Made?
By ERICA GOODE
hen two scientists proposed in a recent book that rape was best viewed as a sexual act with its roots in evolution, it set off a squall of protest from feminists and social scientists, won the researchers appearances on programs like NBC's "Dateline," and became the talk of the cocktail party circuit. Even last week the controversy continued, with the book's authors engaging in a rancorous exchange over a critical review in the scientific journal Nature.
But the case put forward by Dr. Randy Thornhill and Dr. Craig Palmer in "A Natural History of Rape: Biological Bases of Sexual Coercion," published last month by the MIT Press, was not, as some assumed, a fringe theory developed by a pair of renegade researchers.
Rather, the arguments made by Dr. Thornhill and Dr. Palmer fit into a larger theoretical framework, the work of a group of scientists who have ushered Darwin into new and provocative areas, including sexual attraction between men and women, parenting, jealousy and violence, as well as less touchy regions like the learning of language and the organization of perception.
And while some of these researchers, who call their approach "evolutionary psychology" (other scientists view it as only one way of approaching evolutionary psychology), would quibble with some of the methods used and conclusions drawn by the authors of the rape book, most would endorse the larger principles that underlie the work.
The general notion that much of what humans do today evolved in the Pleistocene has seeped into popular culture, and some findings have achieved the status of sound bites: "Men are polygamous, women monogamous," for example, or "Women rank wealth and status higher in selecting a mate; men put a higher priority on reproductive potential." The actor Michael Douglas may have had such precepts in mind when he was asked in a recent interview about his engagement to an actress much younger than he. "It's something that has existed as long as time," he replied. "As long as history there have been older men with younger women."
The scientists whose work is reflected in such statements, albeit in oversimplified form, are not just trying to attract public attention. They are trying to reshape psychology, placing at its center the question of how the mind was "designed" by evolution millions of years ago to solve specific problems faced by human ancestors in an environment very different from the modern world.
In constructing this new psychology, evolutionary psychologists have crafted a novel approach that differs in crucial respects from other, more traditional ways of viewing the mind, and from methods of other evolutionary scientists who study human behavior.
For example, the researchers dispute the view that the human mind is a "general purpose computer" that is programmed by parents, schools and other cultural influences only after birth. They see the mind as preprogrammed, made up of specialized mechanisms -- "modules" or "organs"-- that predispose all human beings to think and act in certain ways, especially when it comes to basic endeavors like selecting a mate, fighting off sexual competitors, or deciding what is safe to eat.
The genes for these complex mental mechanisms, the argument goes, were passed on through the generations because they adaptive, enhancing survival or reproductive success, and eventually, they spread widely and became standard equipment.
But in the year 2000, such mechanisms may or may not be adaptive, and may or may not represent aspects of behavior that society wants to encourage. For example, even if rape was adaptive in the distant past, a notion even many of Dr. Thornhill and Dr. Palmer's like-minded colleagues think dubious, that would not mean that it is excusable or should not be heavily punished.
Evolutionary psychologists argue that their job is to approach the mind as an ancient engineering project, developing and testing out hypotheses about what "design problems" needed solving, and what universal mental structures might have been designed, by the pressures to survive and reproduce, to solve them.
Such an approach, they assert, offers a badly needed bridge between psychology and the natural sciences, and will ultimately provide a much firmer foundation for the understanding of human behavior.
"Psychologists should be interested in evolutionary biology for the same reason that hikers should be interested in an aerial map of an unfamiliar territory that they plan to explore on foot," wrote Dr. Leda Cosmides, Dr. John Tooby, and Dr. John Barkow in the introduction to "The Adapted Mind: Evolutionary Psychology and the Generation of Culture" (Oxford, 1992). "If they look at the map, they are much less likely to lose their way."
Dr. Cosmides and her husband, Dr. Tooby, both professors at the University of California at Santa Barbara, are widely regarded as intellectual leaders of the evolutionary psychology school. Joined by several other scientists, including Dr. Donald Symons, also at Santa Barbara, and Dr. Margo Wilson and Dr. Martin Daly, both of McMaster University in Hamilton, Ontario, they hammered out the basic principles of their approach in the mid-1980's in a series of meetings at a hotel in Palm Desert, Calif.
In the intervening years, this nucleus has expanded to encompass a wide variety of researchers in different areas, including Dr. David M. Buss, a psychologist at the University of Texas, Dr. Thornhill at the University of New Mexico and Dr. Steven Pinker, a psychologist at the Massachusetts Institute of Technology and the author of "Words and Rules: The Ingredients of Language," (Basic Books, 1999) and "How The Mind Works," (W. W. Norton, 1997).
Evolutionary psychologists have not always carried on their campaign quietly.
They have issued a noisy assault on the way the social sciences have done business for the last 50 years, asserting that social scientists have a collective phobia about possible biological influences on behavior and an obsession with more "politically correct" environmental explanations. Some researchers have thrust their work into the spotlight by pursuing topics that seem guaranteed to push people's emotional buttons, rape being only the latest example.
In the process, the scientists have gained a reputation for a self-confidence bordering on arrogance, and a style of scholarly debate so unapologetic and uncompromising that, as one observer put it, "They just make people mad."
Perhaps as a result, the scientists' work and occasionally the scientists themselves have attracted no shortage of criticism, from social scientists and within evolutionary science itself.
Critics have assailed their scientific methods, suggested that some work is tinged by sexism, and have disputed most of the major tenets of the scientists' approach. And some worry that the studies will be misused by politicians and advocacy groups, who are often quick to blur the distinction between theory and fact.
"The fact is," said Dr. Jerry Coyne, an evolutionary biologist at the University of Chicago and a co-author of the critical review of Dr. Thornhill and Dr. Palmer's book in Nature, "that evolutionary psychology, except for its barest claims, remains highly controversial, and there are ideological agendas on both sides."
THE BACKGROUND
A Disturbing Legacy
Of Twisting Darwin
t the most basic level, some critics oppose any effort to link evolution and human behavior.
"There are a whole bunch of people who think it's dehumanizing to talk about humans in biological terms," said Dr. Robert Boyd, an evolutionary anthropologist at the University of California at Los Angeles. "They think it's just kind of distasteful."
In some cases, people confuse the "biological" approach of evolutionary science, which seeks to understand how genes contributed to the evolution of humans as a species, with the field of behavioral genetics, which investigates to what extent heredity accounts for how traits like shyness or schizophrenia vary from person to person.
But biology, applied to human behavior, also has a disturbing history of misuse. College students in introductory courses are taught the perils of "social Darwinism," a 19th-century theory that borrowed catch words of evolutionary thinking and twisted them into a justification for class differences: the struggle for wealth and power, social Darwinists argued, was a battle for "survival of the fittest," a term coined by Herbert Spencer, an English philosopher.
Darwin's theory, stretched and distorted in various ways, was also called upon by the Nazis as a rationale for genocide, and has been a staple of forced sterilization campaigns and racist propaganda.
In the decades after World War II, the record of these abuses created a distrust of biological explanations for human behavior.
But sensitivity could also turn into virtual censorship, as Dr. E. O. Wilson, a renowned entomologist at Harvard, discovered after publishing his now-classic book, "Sociobiology," in 1975. The book, mostly devoted to a discussion of animal behavior, included a final chapter extending evolutionary theory into the realm of human affairs. It was heavily criticized and in 1978, as Dr. Wilson began to speak about his theories at a meeting of the American Association for the Advancement of Science in Washington, protesters heckled him and dumped a pitcher of water on his head.
Dr. Stephen Jay Gould, a paleontologist, and Dr. Richard Lewontin, a population geneticist, both of Harvard, have been the most vocal and prolific of sociobiology's critics, writing a famous 1979 paper, "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Program."
Dr. Gould, in particular, has continued to find fault with the work of scientists, including evolutionary psychologists, who seek to explain traits as "adaptations." In fact, he argues, many traits are not the products of natural selection, favored because they enhance reproduction or survival, but are simply random byproducts of other evolutionary developments.
THE ISSUES
Controversial Task,
Abundance of Critics
ome evolutionary biologists have also historically opposed applying Darwinian principles to humans, not because they have moral misgivings about such research, but because they think the task is simply too complicated.
Trying to determine the evolutionary forces that shaped animal behavior is hard enough, they argue. But to tease out the legacy of evolution from the effects of thousands of years of human culture presents almost insurmountable obstacles, particularly given the limits on the kinds of experiments that can be done with people.
Yet in the last 20 years, advances in genetics and molecular science have made it impossible to ignore the evidence that biology has at least some impact on how people behave and have made the discussion of genetic influences more widely accepted.
And evolutionary scientists, able to go about their work in a more tolerant climate, have begun to develop a variety of methods for applying Darwinian principles to humans. Evolutionary psychology, as defined by Dr. Cosmides, Dr. Tooby, and others, might involve laboratory experiments, cross-cultural studies and other approaches.
Other researchers use mathematical models to study foraging and other behavior in modern hunter-gatherer societies. Still others do comparative studies, looking for similarities and differences between humans and animals.
And the Human Behavior and Evolution Society, founded 15 years ago, counts 1,000 members from a wide variety of disciplines, including biology, psychology, anthropology, law and medicine, who study topics as diverse as the way pheromones coordinate female menstrual cycles and hunting practices among the Ache of Paraguay.
Still, some evolutionary psychologists feel their arguments for biology must overcome substantial resistance. "There is a flagrant double standard that's applied to the evidence," said Dr. Buss, whose latest book, "The Dangerous Passion" (Free Press, 2000) deals with jealousy, and who has recently proposed that human beings may have a specialized mental module for murder.
"If it's an evolutionary hypothesis, you have to document mountains of evidence before anyone will take it seriously, and even then it will be dismissed," Dr. Buss said. "On the contrary, if you say there is a sex difference and it's all due to media violence, then the standards are low and everyone accepts it without any evidence."
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