Question: Are women more cooperative than men?
Suppose you are a participant in one of our psychology experiments at the VU University-lab in Amsterdam (or, for that matter, in a different lab in some other part of the world). You will be playing a game with another person - who you do not know and shall never meet again--for money. If you both cooperate you will each earn a modest amount of money, say $10. If neither cooperates, each of you receives an even smaller amount - say, $2. Yet if you cooperate and your partner does not then he or she receives $40, while you end up with nothing. What do you do -- cooperate or cheat? You'd probably respond: "Well it really depends who I am playing against." And indeed it does, and in a surprising way.
New research from my colleague Daniel Balliet at the VU University and myself, together with researchers from Singapore Management University (Norm Li) and Washington State University (Shane MacFarlan), published in the prestigious APA-journal Psychological Bulletin, suggests that whether you cheat or cooperate in this so-called prisoner's dilemma game really depends.....upon the sex of the other player.
Our research team conducted a meta-analysis of 272 studies, conducted over 50 years, comprising 31,642 participants in 18 countries. Most of the studies were conducted in the United States, the Netherlands, England and Japan and all of them reported the sex of the players.
The first surprising result was that there is no statistical difference between the sexes when it comes to overall levels of cooperation. Thus men and women are equally cooperative. This contradicts the common stereotype that women are more prosocial than men.
But perhaps the most surprising finding - across many studies over 5 decades of research -- is that men actually cooperate more with other men than do women cooperate with other women.
Now this really turns the world upside down. We have been bombarded with bestselling books about gender differences with the take-home message that "Men are from Mars and Women are from Venus." Our results suggests the opposite. Men and women may be on different planets, but perhaps it is the men coming from Venus (named after the Roman goddess of love) and the women from Mars (named after the Roman god of war).
How do we explain this robust finding? Our research tested an evolutionary psychology prediction against a socio-cultural one. Socio-cultural theory suggests that due to different socialization processes women are socialized into more caring roles than men and, as a result, women are more cooperative. But this is not what the meta-analysis shows. If we want to understand why female solidarity is not so strong in these studies, we may need to delve deep into human evolutionary history.
Our ancestors were nomadic hunter-gatherers who lived together in small bands and, to avoid inbreeding, there was migration between neighboring groups. Anthropological research suggests that it was usually the women who moved between the groups. The consequence of this is that these women would have been interacting mostly with women who were not their relatives. Sexual competition between them may have dealt a further blow to female solidarity.
But why should male solidarity be stronger? Well, first of all, the men in the group were probably related to each other, ensuring that they have overlapping interests. Further, for collective tasks such as hunting and warfare the men would have had to form alliances with each other. Hunting and warfare are classic prisoner's dilemmas and they can only be solved with trust and cooperation. Thus, male solidarity might have evolved essentially for organizing fighting parties. There is some evidence for this "male warrior" hypothesis from our own studies (included in the meta-analysis). These experiments show that men cooperative more with the group when it is being threatened by a rival group.
So maybe there is some truth to the saying that "Men are from Mars and Women from Venus" after all. Remember that Mars is the highly revered Roman god of warfare. Yet -- paradoxically -- to win a war actually requires men to work closely together and this explains the evolution of male solidarity.
A final note on this research. There is a lively debate in our field about whether humans are more like chimpanzees or bonobos - both of them are our nearest primate cousins. Although the meta-analysis does not directly speak to this, female solidarity is more common among bonobos, whereas male solidarity is more typical of chimpanzees. Thus, although humans are genetically as close to the chimp as the bonobo, our social behavior resembles more chimpanzee society than bonobo society -- whether we like it or not.