This article is from PLoS ONE , volume 9 . Abstract Parochial altruism, defined as increased ingroup favoritism and heightened outgroup hostility, is a widespread feature of human societies that affects altruistic cooperation and punishment behavior, particularly in intergroup conflicts. Humans tend to protect fellow group members and fight against outsiders, even at substantial costs for themselves. Testosterone modulates responses to competition and social threat, but its exact role in the...
Source: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4116333