It’s practically a truism: Men are competitive, whereas women are cooperative. But truisms can be misleading. When it comes to popular stereotypes about aggressive, dominance-seeking men and nurturing, relationship-oriented women, exceptions abound. One such exception—the willingness to cooperate with members of the same sex despite differences in rank—has become the subject of academic research. Thus far, research indicates that women of different social or professional ranks cooperate with each other less well than men do.

The latest results appeared March 3 in Current Biology, in a paper entitled “Rank influences human sex differences in dyadic cooperation.” This paper, prepared by researchers at Harvard University, Emmanuel College, and the University of Quebec at Montreal, noted that unrelated human males regularly interact in groups, and that the groups often include higher and lower ranked individuals. Yet this kind of cooperation, asserted the researchers, seems less common among women, who often reduce group size to interact with only one individual of equal rank.

To test whether men were more apt than women to engage in same-sex, cross-rank cooperation, the researchers examined subjects who were, in a sense, close to home. That is, they looked at other academics and their patterns of authorship. In the Current Biology paper, the researchers wrote: “Numbers of co-authored peer-reviewed publications were used as an objective measure of cooperation, and professorial status as a measure of rank.”

Ultimately, the authors confirmed that men tend to cooperate more than women with same-sex individuals of differing rank: “Among those of equal status (full professors) there was no gender difference for likelihood of co-authorship: Women and men were equally likely to co-author publications with another full professor of the same gender. In contrast, male full professors were more likely than female full professors to co-author publications with a same-gender assistant professor.”

According to the authors, their findings shouldn’t be all that surprising. The male capacity for cooperation with other males across lines of hierarchy is reflected in behavioral tendencies that span age groups and even species.

“When I studied young children, I noticed that boys were typically interacting in groups, and girls tended to focus on one-on-one relationships,” said Joyce F. Benenson, the study’s lead author and an Associate of Harvard’s Human Evolutionary Biology department and Professor of Psychology at Emmanuel College. “There is even evidence that these differences exist in six-month-olds—but you can see it with the naked eye by about five or six years old, where boys form these large, loose groups, and girls tend to pair off into more intense, close friendships.”

What makes those differences particularly provocative, Benenson noted, is that chimpanzees organize their relationships in nearly identical ways.

“Chimpanzee males usually have another individual they’re very close with, and they may constantly battle for dominance, but they also have a larger, loose group of allies,” Benenson added. “When it comes to defeating other groups, everybody bands together. I would argue that females don’t have that biological inclination, and they don’t have the practice.”

According to study co-author Richard Wrangham, the Ruth Moore Professor of Anthropology and chair of Biological Anthropology at Harvard, the presence of such diverse examples of male cooperation—among children, chimpanzees, and now publishing academics—“pushes into thinking that there is a strong biological influence here, but we would never suggest this is impervious to environmental and cultural influences as well.”

“Nevertheless these are the kinds of fascinating questions about fundamental sex differences in social relationships that would be tremendously important to recognize if you want to change the way in which women’s access to higher ranks happens,” he added. “What we need to know, now that we have recognized these patterns, is what can we do to ameliorate them?”

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