The behaviour is particularly attractive to women, although men also rate it highly.

Being altruistic - helping others without thought of reward - is particularly attractive to women, research finds.

But both men and women find those who are altruistic more attractive.

The results come from three studies including over 1,000 people.

People were asked about the behaviours they looked for in a mate.

Some of the suggested behaviours included donating blood and volunteering in a local hospital.

Women were more keen on these altruistic traits in a potential partner.

Dr Tim Phillips, the study's first author, explained that humans were not the only species to display altruism:
"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."
In a subsequent study, researchers asked people in couples how much they appreciated altruistic behaviour.

Those that preferred altruistic traits had partners who displayed these more.

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 Tom Reader, who co-authored the study, said:
"Sexual preferences have enormous potential to shape the evolution of animal behaviour.

Humans are clearly not an exception: sex may have a crucial role in explaining what are our most biologically interesting and unusual habits."
The study was published in the British Journal of Psychology (Phillips et al., 2008).