A Scottish research suggests that being nice or being nasty is in your genes - particularly if you're a woman.
The study of almost 1,000 pairs of identical and non-identical twins, conducted by psychologist Gary Lewis and colleagues at Edinburgh University, has found that genetic factors appeared to affect how likely someone was to do charitable deeds or work hard in their job.
However, the experts also said the environment in which we live still plays a part in how nice we are, meaning we cannot just blame our genes if we're feeling a bit nasty.
Comparing them to non-identical twins, whose genes vary, allows researchers to look at what impact genetics has in certain situations compared to other factors such as the environment in which they live.
The researchers looked at levels of "prosociality" - meaning contributing to the civic duties of society such as carrying out jury service, going beyond the call of duty at work and paying higher taxes to help other people.
The twins were asked to rate on a scale of zero to ten how much obligation they felt in areas such as testifying in a court case, working longer than their normal hours and carrying out charity work.
"What we found is that identical twins were much more similar in their responses to these types of questions than were non-identical twins," the Scotsman quoted Lewis as saying.
"These domains of prosocial obligations were quite highly associated with each other, suggesting that if you are nice in one area, you are likely to be nice in another area.
He added: "So there is a general prosocial personality that seems to be present.
"For women, this general prosocial personality had about half of its influence generated by genetic factors and the other half by environmental factors.
"But for men the genetic influences were much more modest, with about 20 per cent of the influence genetic and the rest appeared to be environmental."
Lewis said genetic factors were not the only influences on people's personalities and levels of niceness.
"We commonly, at a layman's level, think that the environment is the overriding factor," he said.
"But what these results suggest is that genes are important as well, but it certainly isn't saying that the environment isn't a considerable factor also.
"So it is saying genes are there in some sense - it is not the critical factor, but it is by no means a trivial factor, but much more so in women than in men," he added.
The study has been published in the journal Biology Letter.