There is genetic evidence that selfless or altruistic behaviour may have evolved because it was one of the qualities our ancestors looked for in a mate.

This is the finding of Dr Tim Phillips and colleagues from the University of Nottingham and Institute of Psychiatry, King's College, London whose results were published in the British Journal of Psychology.

The study investigated whether altruistic behaviour evolved as a result of sexual selection. 70 identical and 87 non-identical female twin pairs completed questionnaires relating to their own levels of altruism (e.g. "I have given money to charity") and how desirable they found this in potential mates (e.g. "Once dived into a river to save someone from drowning").

Statistical analysis of their responses revealed that genes influenced variation in both the subjects' preference towards a mate and their own altruistic behaviour -- an indication that sexual selection might be at work.

Interestingly, there was also a genetic correlation between the two. This suggested that, in our evolutionary past, those with a stronger mate preference towards altruistic behaviour mated more frequently with more altruistic people, thus further supporting a link with sexual selection.

Tim explained: "These results are consistent with a link between human altruism towards non-relatives and sexual selection and throws an exciting new light on the puzzle of altruistic behaviour -- which appears, at first sight, to be at odds with evolutionary theory."

"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 so led to a link between human altruism and sexual selection."