MEN really are more selfish because testosterone makes them forget fairness, a study suggests.
Their reputation for being thoughtless lovers and hard-nosed colleagues was linked to the male sex hormone.
Higher levels of testosterone were found to lead to “decisions that prioritise selfish motives over fairness”.
In a test, 110 young men, half of whom were treated with a rub-on testosterone gel, were told to split a pot of money between themselves and another person who was not in the room.
Men given the testosterone were greedier and kept significantly more cash, while the others chose a fairer split.
Researchers think the motive is to try to boost earnings and social status as, historically, this would have improved their chances of finding a mate and having children.
Hong Kong-based Dr Yin Wu said: “Testosterone biased men to prioritise their selfish interests.”
He said men might be more generous if watched, so they did not get a bad reputation, but were greedier behind closed doors.
He added: “These findings shed new light on the function of testosterone in social decisions that involve a trade-off between personal interests and fairness.
“It increased the desire to be better off than others.”
A 2017 study backed up the theory when it found the female brain responds differently after good deeds.
Experts led by Zurich University showed women got a bigger rush of the feel-good chemical dopamine than men when they donated money to someone else.
Men naturally have about ten times as much testosterone as women.