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Forget nature versus nurture. From cooperation to social stigma, morality to mating, evolutionary adaptation is the key to understanding human behavior, says Penn psychologist Robert Kurzban.

By Julia M. Klein


We’ve arrived a bit early at McFadden’s, a cavernous wood-paneled bar situated in the urban wasteland between hip Old City Philadelphia and up-and-coming Northern Liberties. It is nearly empty, but “Ed”—a 33-year-old engineer from the suburbs who prefers to remain anonymous—is already here, sitting on a bar stool, awaiting the start of another HurryDate party.

Ed is a veteran of these gatherings, at which men move between tables for a series of four-minute dates with a dozen or more women of similar ages. Afterwards, participants indicate their choices—people they’d like to see again—and are sent any matches by e-mail. Ed, attractive, personable, and looking to start a family, says he usually receives a couple of matches after a HurryDate event. But not a single woman has responded to his request for a real-life date. “I find they don’t follow up,” he laments.

Beer in hand, Robert Kurzban, assistant professor of psychology at Penn, nods sympathetically. This puzzling non-responsiveness may be bad news for Ed. But it is excellent news for Kurzban, buttressing his current theory about HurryDating preferences. “This is exactly what we find in our data,” he says quietly. At these events, “people are shifting into a short-term mating mode,” even if they say they are looking for a long-term partner. That means women, just like men, tend to choose largely on the basis of physical attractiveness, disregarding factors such as income and social status.

The HurryDating women are “very driven by the local environment,” says Kurzban, who hypothesizes that both the bar setting and the intoxicating presence of so many prospective partners may trigger short-term mating behavior. “And once they get to a different environment”—for instance, back home—“their preferences are very different.” And they don’t seem to include Ed, who, despite many fine attributes, is no Bill Gates.

The 36-year-old Kurzban has attracted national media attention this past year for his work on HurryDating. It’s a new direction for him. In the past few years, he has won recognition for research on topics such as coalitional psychology, social stigma, race, and moralistic punishment. Cross-trained in economics and anthropology, and known for his broad range of interests, Kurzban was the chief organizer this year of the annual conference of the Human Evolution and Behavior Society, held at Penn in June and attended by leading figures in the field of evolutionary psychology [See sidebar].

“Rob is already a superstar in evolutionary psychology, and he’s a rising star in social science at large,” says Martie G. Haselton, associate professor of communications studies and psychology at the University of California at Los Angeles. “He’s been a real pioneer—the first to explore several topics, including serious applications of evolutionary principles to experimental economics. This work has ramifications for understanding one of the most vexing problems of human existence: how to get people to cooperate.”

Kurzban is “a Renaissance man,” says Leda Cosmides, whose 1992 book, The Adapted Mind, co-authored with her husband, John Tooby, is considered one of the founding documents of evolutionary psychology. “Rob’s a brilliant guy, and he’s very creative, and that’s why he can do such high-quality work in so many areas.”

Kurzban says his greatest intellectual joy derives from applying the evolutionary paradigm, which sees human psychology in terms of evolved adaptations, to a range of problems in social psychology and other disciplines. “To be able to read different literatures—for example, the social stigma literature, the literature of morality, the literature of leadership—and apply an evolutionary analysis has been the exciting thing for me,” he says, “because all of these things allow us to take a large body of research that’s been done and look at it in a way that hasn’t been applied before. And that’s why you see me moving from cooperation in groups to morality to mating.” In each case, he says, re-thinking existing data using an evolutionary approach can “lead to what, I hope, are new insights, as well as new empirical work that allows us to make progress.”


Kurzban’s own progress through academe has involved some detours. Raised in Poughkeepsie, New York, he attended Cornell University as an undergraduate, switching his major from biology to psychology. He attributes his interest in evolutionary psychology to “a couple of really important moments,” including his discovery of Margo Wilson and Martin Daly’s classic 1988 book, Homicide, and a talk by David M. Buss, now professor of psychology at the University of Texas at Austin and author of The Evolution of Desire: Strategies of Human Mating (1994; revised in 2003).

“If you really want to trace the roots [of evolutionary psychology], you start with Darwin obviously,” says Kurzban, but the discipline’s more recent forebear is sociobiology, the controversial Darwinian study of animal and human behavior introduced by Harvard entomologist E.O. Wilson in his 1975 book, Sociobiology: The New Synthesis. The reliance on evolutionary models to explain human behavior made headlines at the time, and Wilson, an ant expert, was widely derided as a biological determinist, a defender of the status quo, and even a racist.

Since then, however, sociobiology has birthed two disciplinary offspring: Human behavioral ecology, which studies real-life fitness outcomes, and evolutionary psychology, which focuses on what Tooby and Cosmides called “the adapted mind.” Although the evolutionary paradigm still has its critics, who say it undervalues the role of culture, its influence is, without doubt, spreading and transforming both the social sciences and humanities.

Integral to evolutionary psychology is the notion of modularity. “In the same way that you’ve got a liver and a kidney which do special things,” Kurzban explains, “you have things in your brain which do special things. So we shift the debate from nature-nurture, which we think is not an interesting way to frame it, to, ‘What are the functional mechanisms in your head that do really specific jobs?’ We see ourselves as reverse engineers. We take a thing, look at what it does, and then try to figure out how it was built.”

Kurzban recalls his early excitement at the field’s potential. “Once you shine that conceptual light on questions in psychology, I see vistas of research opening up—and clarity of thought that was very enticing [to me] as a young person,” he says. “And still is.”

But first, after graduating from Cornell in 1991, he decided to indulge another love. “I’ve always been a big fan of Disney,” he says. Though he’d been told no jobs were available, he loaded up his Nissan Sentra and drove to the company’s headquarters in Orlando, Florida. When he arrived at the “casting office,” he recalls, “their interview was one question: ‘Why do you want to work at Disney?’ I told them I loved it and wanted to be part of the family. And they asked me when I could start.” (If only landing academic jobs were as easy…)

For six months, Kurzban worked at Epcot Center, running attractions, and then, with his high-school French, snared a gig at Euro Disneyland a few miles east of Paris. He sent his graduate school applications off from France.

When Cosmides, now co-director of the Center for Evolutionary Psychology at the University of California at Santa Barbara, agreed to accept Kurzban as a student, “that was a pivotal moment in my trajectory,” he says. In truth, he had hoped for the chance to study with Buss, then at the University of Michigan, but was turned down. Over time, though, the emphasis at Santa Barbara on social psychology served him well. “The fit there turned out to be very good,” he says.

His next step was two years of post-doctoral work at the University of Arizona, at the behavioral economics laboratory of Vernon Smith, who would go on to win the Nobel Prize in economics. Kurzban says the methods he learned there—including using real money in experiments to gauge costs and benefits to his subjects—remain part of his laboratory practice today.

Then came two more years as a post-doc, split between the California Institute of Technology’s Division of Humanities and Social Sciences and the University of California at Los Angeles’ anthropology department. “Four years of post-doc is unusual,” Kurzban says candidly. “You start asking yourself, ‘Why can’t this guy get a job?’”

And, for a while, he couldn’t. “I applied every year of my post-doc,” he says. “It was a tough time, not that many people really want to hire someone trained like me, my publication stream was not as strong as it could have been, the market is fickle—that’s hard. But if we’re going to be honest, I was looking for a job, and I couldn’t get one, and I feel very lucky to have had the opportunity to come here to Penn.”

At Penn, Robert Seyfarth, professor of psychology and an expert on animal behavior, says that the department was eager to increase its strength in evolutionary psychology, “a really exciting area.” Kurzban, he says, is “part of a new wave of social psychologists” emphasizing evolutionary approaches, and his ability to integrate work in decision sciences and economics with evolutionary theory and social psychology made him particularly attractive. For his part, Kurzban, who came to Penn in the fall of 2002, says he appreciates the strong biological grounding of the University’s psychology department.

This spring, Kurzban taught a 9 a.m. undergraduate class on human sexuality, in which sufficiently caffeinated students caught flashes of his wry wit. “OK, number of sexual partners is something that people are very interested in,” he said as he quickly reviewed survey data. “People around the world have an average number of 10.5 sexual partners. Typically, people’s actual number of sexual partners is an integer.”


Later, over tapas at a chic Spanish restaurant in Old City, Kurzban uses the objects at hand to explain how evolutionary psychologists work.

“If you want to claim that something is an adaptation, that something is designed to serve a particular function,” he says, “then you need to show evidence of special design.” He pauses between bites of elegantly sauced morsels of chicken to ruminate on his utensils.

“If I wanted to say that this is a knife, whose function is cutting, it would be very nice to be able to show that it had a sharp edge and it had a handle, it had a certain heft.” He turns it over to demonstrate the point, then draws out the analogy: “If I could only look at this obliquely, which is what happens in psychology, then I might have to do some wriggling to see whether or not the blade is really sharp. And I might have to put it through lots of different tests. And that’s what we do in the laboratory.”

Kurzban has focused mostly on human “sociality,” as opposed to mating, which preoccupies many evolutionary psychologists. “Really what I think about is, ‘What are the human adaptations designed for social interaction?’” he says.

Cosmides particularly values Kurzban’s work on coalitional psychology and the psychology of collective action. Using the techniques of experimental economics, Kurzban has described how “people regulate their levels of cooperation when there is a public good,” she says. Specifically, he has shown that in a situation where people are not allowed to punish “free-riders” (those who don’t do their share), people “ratchet down” their contributions, causing “the whole operation to unwind.”

Such work, though not politically motivated, has obvious political implications, Cosmides says. She notes how disastrous collectivized agriculture proved in the old Soviet Union. “I think Rob’s work shows why.”

Kurzban’s most-cited contribution is a 2001 theory paper on stigma, co-authored with Wake Forest University’s Mark R. Leary. He explains: “That paper essentially says: ‘This category that social psychologists have been using—it’s not one thing, it’s multiple things, and those different things can be understood in the context of different adaptive problems and different adaptive mechanisms to try and solve them.’” Stigma is useful, Kurzban says, to avoid disease, “bad social exchange partners” (for instance, people who are unpredictable, dishonest, or poor), and “bad coalition partners.”

Daphne B. Bugental, professor of social and developmental psychology at the University of California at Santa Barbara, says that previous researchers have concentrated on “what stigma is, how it operates, and who is affected,” while “Kurzban’s approach addresses the basic why question.” Because he suggests that people sometimes avoid people with physical disabilities because they are responding to “ancient markers of risk” that may no longer be relevant, she says, his research could help combat prejudice. So, too, she says, could his “ground-breaking” work on race.

In “Can race be erased? Coalitional computation and social categorization,” co-authored with Tooby and Cosmides in 2001, Kurzban reports an experiment that showed that when race doesn’t correspond with alliances, “subjects markedly reduce the extent to which they categorize others by race, and indeed may cease doing so entirely.” That research is a good example of how the evolutionary paradigm can generate testable hypotheses. “Humans would not have been evolving in a world where there were different races around, although there would have been people of different ages and sexes. So race should be very different from age and sex,” says Kurzban. “The claim in the literature was that categorizing people by race was done automatically. And that paper shows it’s not automatic.”

Because of their essentialist leanings, evolutionary psychologists are sometimes accused of being “right-wing fascists,” in Kurzban’s phrase. But the race paper provoked e-mails charging that he was “pandering to left-wing liberals.” As a scientist, he shrugs off such reactions: “All I know is: Here are the data. If people have some political agenda they want to use it for, that’s actually not my business—or my problem.”

One of Kurzban’s current projects—an ambitious theory paper being considered for publication in the prestigious Personality and Social Psychology Review—also appears destined to provoke controversy. Titled “Modularity and the Social Mind: Are Psychologists Too Self-ish?,” it challenges the idea of the unitary “self,” as well as the importance of the notion of self-esteem. Attempting to explain why people often can’t enunciate a rationale for their own decisions, Kurzban and co-author C. Athena Aktipis, a doctoral student at Penn, posit that different parts of the mind have different functions that aren’t always transparent to one another. “People aren’t going to like it,” Kurzban says, “but hopefully it will get a discussion going.”

Another paper, accepted by the journal Evolution and Human Behavior, takes a look at moralistic punishment. In two experiments, Kurzban found that if punishing cheaters by docking their pay entails an economic cost to the punisher, people are more likely to impose punishments when they are being observed. “Let me make an important distinction: People like wrongdoers to be punished,” he says. But “once an individual has to bear the cost of inflicting this punishment [him- or herself], they don’t actually seem all that willing” to do it. (“I think that’s exactly why we have things like a justice system,” he adds.)

“The argument,” he continues, “is [that] where you do see some punishment is when you get a reputational benefit from it. So we think that the story here might be one in which moralistic punishment is a signaling act,” meaning that it indicates something positive about the punisher. But, he says, “I wouldn’t take that one to the bank right now.” Another piece of the puzzle is gradually being filled in: Data collected by Kurzban’s students show that “people who punish a moderate amount are construed more favorably than people who don’t punish at all.”


Kurzban’s involvement with HurryDate was a matter of both serendipity and scientific opportunism.

In the fall of 2002, when he was still new to Philadelphia, Kurzban spotted an advertisement for the service on SEPTA. This, he realized immediately, was a chance to get “real-world data” that would look at people’s mating preferences in “a behavioral way.” Most studies on mating have relied on stated desires. With HurryDate, people’s choices would have actual consequences: at the very least, the exchange of e-mail addresses with prospective dates.

So Kurzban contacted Adele Testani, president of the Manhattan-based company. “I said, ‘I’m a scientist. I want to do research on what people do in these environments. Can I have your data?’ ” Happily for science, Testani agreed.

HurryDate typically surveys customers about their background, including income, race, and religion. Kurzban and a colleague, Jason Weeden G’00 Gr’03, also asked volunteers about their own attractiveness, values, and desire for children. “In retrospect, it turns out this was a very good idea, a gold mine,” Kurzban says.

As predicted by evolutionary psychology, the two men found that there appeared to be a “mating market,” in which certain prospective partners had a high value, and those who had less to offer seemed to know it. “So the undesirable men are saying ‘yes’ to the highly desirable females but the highly desirable females aren’t saying ‘yes’ to them,” explains Kurzban. And “the people who are getting fewer ‘yeses’ are themselves saying ‘yes’ more.”

But the women’s emphasis on male attractiveness surprised the researchers. So Kurzban, who, with Weeden, is working on a second paper on “Stated Versus Revealed Mate Preferences,” is only too happy to spend an evening at McFadden’s, beer in hand, trying to figure out why these young men and women behave as they do. To make it all the pleasanter, he is accompanied by his “SO,” or significant other, a graduate student in evolutionary psychology at another university.

She is young and pretty, precisely the attributes that the evolutionary paradigm says he should prefer. But her looks are “not her best feature,” Kurzban is quick to say. He makes a point of praising her intellect and character, suggesting that he may, in fact, have some long-term mating goals of his own. Meanwhile, chatting with the HurryDaters about their expectations is proving useful. “This makes me believe my own data,” he says.


Julia M. Klein, a cultural reporter and critic in Philadelphia, writes for The New York Times, The Wall Street Journal, Mother Jones, and many other publications.

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