  Differences between men and women have intrigued generations of social
scientists, who have found that the two sexes behave differently in settings
requiring competition, risk taking, altruism, honesty, as well as many others.
Yet, little is known about whether there are gender differences in cooperative
behavior. Previous evidence is mixed and inconclusive. Here I shed light on
this topic by analyzing the totality of studies that my research group has
conducted since 2013. This is a dataset of 10,951 observations coming from
7,322 men and women living in the US, recruited through Amazon Mechanical Turk,
and who passed four comprehension questions to make sure they understand the
cooperation problem (a one-shot prisoner's dilemma). The analysis demonstrates
that women are more cooperative than men. The effect size is small (about 4
percentage points, and this might explain why previous studies failed to detect
it) but highly significant (p<.0001).
