Women have a stronger genetic predisposition to help other people compared with men, according to a study that has found a significant link between genes and the tendency to be "nice".
The research, based on an analysis of nearly 1,000 pairs of identical and non-identical twins, found that about half of "prosocial" traits – the willingness to help others – identified in women could be linked with genes rather than environmental upbringing, whereas the figure was just 20 per cent in men.
Scientists believe the findings lend further support to the idea that prosocial behaviour has a strong heritable component with some people displaying an innate tendency from childhood.
One conclusion from the study, published in the journal Biology Letters, is that some women, and rather fewer men, find it easier than the rest of the population to be generous and helpful towards others, given the right sort of upbringing.
"There is a very big debate at the moment about whether humans are altruistic or not," said Gary Lewis, a psychologist at the University of Edinburgh who carried out the research. "There are some people who argue that we have evolved to be altruistic independently of external interventions, and others who argue that we are rather selfish and need a rather conducive external environment for us to be nice to others.
"This work suggests there could be different types of people out there in the world, with some finding it easy to be prosocial, and others who need to have help on the way," he said.
Researchers interviewed the sets of twins by asking them questions about whether they would be willing to appear in court after a traffic accident, or whether they felt obliged to pay higher taxes in order to fund other people's healthcare. By using identical twins, who share both genes and upbringing, and non-identical twins, who share upbringing but not all genes, the investigators were able to tease apart the role of nature and nurture in the personality types they identified.
"It seems that there is a general prosocial personality. I wouldn't go as far as to say they are nice people, but they are certainly prosocial people," Mr Lewis said. "We found that in women there was quite a strong genetic influence on this type of prosociality but in men there was less of a genetic influence. There were also environmental influences in both cases that were quite sizeable.
"For women on this general prosociality personality it was about half and half: genetic factors were about 50 per cent. For men, it was less genetically influenced. About 20 per cent of this general prosociality personality had a genetic basis," Mr Lewis said.
"What we are really saying here suggests interventions that encourage socially conscious behaviours may be useful but some individuals may be instinctively more prosocial than others."