New research carried out by biologists and a psychologist at The University of Nottingham has revealed that displays of altruism or selflessness towards others are seen by females as the most attractive trait in a partner.
In three studies of more than 1,000 people Dr Tim Phillips and his fellow researchers discovered that women place significantly greater importance on altruistic traits that anything else.
The study has been published in the British Journal of Psychology.
Dr Phillips said: "Evolutionary theory predicts competition between individuals and yet we see many examples in nature of individuals disadvantaging themselves to help others.
"In humans, particularly, we see individuals prepared to put themselves at considerable risk to help individuals they do not know for no obvious reward."
Participants in the studies were questioned about a range of qualities they look for in a mate, including examples of altruistic behaviour such as 'donates blood regularly' and 'volunteered to help out in a local hospital'. Women placed significantly greater importance on altruistic traits in all three studies.
Yet both sexes may consider altruistic traits when choosing a partner. One hundred and seventy couples were asked to rate how much they preferred altruistic traits in a mate and report their own level of altruistic behaviour.
The strength of preference in one partner was found to correlate with the extent of altruistic behaviour typically displayed in the other, suggesting that altruistic traits may well be a factor both men and women take into account when choosing a partner.
Dr Phillips said: "For many years the standard explanation for altruistic behaviour towards non-relatives has been based on reciprocity and reputation - a version of 'you scratch my back and I'll scratch yours'. I believe we need to look elsewhere to understand the roots of human altruism.
The expansion of the human brain would have greatly increased the cost of raising children so it would have been important for our ancestors to choose mates both willing and able to be good, long-term parents. Displays of altruism could well have provided accurate clues to this and genes linked to altruism would have been favoured as a result."
Dr Phillips concluded: "Sexual selection could well come to be seen as exerting a major influence on what made humans human."