Two experiments were undertaken. For the first, 65 men and 65 women, all of an average age of 21, anonymously played a cooperation game where they could donate money via a computer program to a group fund. Donations were selfless acts, as all other players would benefit from the fund, whilst the donor wouldn’t necessarily receive anything in return.

Players did not know who they were playing with. They were observed by either someone of the same sex or opposite sex — two physically attractive volunteers, one man and one woman. Men were found to do significantly more good deeds when observed by the opposite sex. Whilst the number of good deeds made by women didn’t change, regardless of who observed.