Stereotypes suggest women are more cooperative than men, but an analysis of 50 years of research shows that men are equally cooperative, particularly in situations involving a dilemma that pits the interests of an individual against the interests of a group.

Additionally, men cooperate better with other men than women cooperate with each other, according to the research, published online by the American Psychological Association in Psychological Bulletin. Women tend to cooperate more than men when interacting with the opposite-sex, the analysis found.

The researchers conducted a quantitative review of 272 studies comprising 31,642 participants in 18 countries. Most of the studies were conducted in the United States, the Netherlands, England and Japan. The articles were written in English and had to contain at least one social dilemma. Social dilemma experiments involve two or more people who must choose between a good outcome for themselves or a good outcome for a group. If everyone chooses selfishly, everyone in the group ends up worse off than if each person had acted in the interest of the group.

While there was no statistical difference between the sexes when it came to cooperating when faced with a social dilemma, when the researchers drilled down they did find some differences. Specifically, women were more cooperative than men in mixed-sex studies and men became more cooperative than women in same-sex studies and when the social dilemma was repeated.

The "prisoner's dilemma" was the most commonly used experiment in this meta-analysis. In this interaction, a pair of people must decide whether to cooperate or defect. If they both cooperate, each person receives a modest amount of money, such as $10. However, if only one person cooperates, then the defecting participant receives more money, such as $40, while the cooperating person receives nothing. If both people decide to defect, they would each receive a small amount  say, $2.

"It is a social dilemma because each individual gains more by defecting regardless of what the other person does, but they will both be better off if they both cooperate," said the study's lead author, Daniel Balliet, Ph.D, of the VU University Amsterdam.

Even though most of these experiments were conducted in laboratories, social dilemma experiments have been shown to predict cooperation outside the laboratory very well. The authors used socio-cultural and evolutionary perspectives to explain some of the findings, particularly why men were found to be more cooperative than women during same-sex interactions.

"The argument is that throughout human evolutionary history, male coalitions have been an effective strategy for men to acquire resources, such as food and property," said Balliet. "Both hunting and warfare are social dilemmas in that they firmly pit individual and group interests against each other. Yet, if everyone acts upon their immediate self-interest, then no food will be provided, and wars will be lost. To overcome such social dilemmas requires strategies to cooperate with each other."

Evolutionary theory may also explain why women are less cooperative with other women when faced with a social dilemma, according to Balliet. "Ancestral women usually migrated between groups and they would have been interacting mostly with women who tended not to be relatives, and many were co-wives," he said. "Social dynamics among women would have been rife with sexual competition."

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