Men donate more money to charity if they see other males have donated large amounts. And they'll also be more generous if the person asking for money is an attractive woman. (Surprise, surprise).
These are the key findings of a large study that examined why people are generous when there's nothing in it for them.
While similar studies have been conducted in controlled laboratory settings, this is one of the first to observe such behaviours in real life. The UK researchers analysed information from people raising money for different causes online. In each case donors could see a picture of the person asking for money, and the gender and amount donated by others.
The effect of other men posting large donations or an attractive female asking for money on a man's generosity was significant. Their giving was four times greater in those instances than if they were asked for money by a man, a less attractive female or if there was no large bids from other males.
Combine the two scenarios together and the donation was even bigger.
Women, however, did not feel compelled to donate more when the person asking was an attractive man – or if other women had donated large amounts.
Evolutionary biologist Rob Brooks said while the motivation for reciprocal altruism (I'll scratch your back if you scratch mine) was obvious, scientists didn't totally understand unconditional generosity.
While donations to online charities could generally be seen as unconditional, the study also showed complex layers of social signalling were involved in the mix.
"That starts to erode the unconditionality of it because you can see men are beginning to compete with each other," said Professor Brooks from the University of NSW.
"Overt generosity can be a competitive rather than a co-operative act," said the researchers, who published their findings in the journal Current Biology.
That men's generosity could be influenced by these factors did not surprise Professor Brooks, especially given the way male-to-male competition shaped many social situations.
"So much of what we do is modified by the possibility of sex in the future," he said.
But for those concerned about what the study observed, Professor Brooks, who was not involved in this research, said these behaviours are not inevitable.
"This tells us what people are doing, it doesn't tell us what they should be doing," he said.
