For the second experiment, groups of males were formed. Males were asked to make a number of public donations. These increased when observed by an attractive female, where they were found to actively compete with one another. When observed by another male, however, donations didn’t increase.

Dr Iredale said: “The research shows that good deeds among men increase when presented with an opportunity to copulate. Theoretically, this suggests that a good deed is the human equivalent of the peacock’s tail. Practically, this research shows how societies can encourage selfless acts.”