Men are more jealous than women in heterosexual relationships, it turns out - and the difference is driven by men's ingrained fear of fathering someone else's child.
A group of researchers at Chapman University in the US carried out a poll on 64,000 Americans, asking them to describe how they would feel if their sexual partner was unfaithful.
"Heterosexual men really stand out from all other groups: they were the only ones who were much more likely to be upset by sexual infidelity,”explained professor David Frederick, lead author of the study.
The poll included both heterosexual and homosexual men and women, but by far the most jealous were straight men, of whom 54 per cent of said they would be very distressed by it, compared to 35 per cent of straight women.
Bisexual men and women did not differ from each other significantly. Gay men and lesbian women were the same.
This heterosexual gender difference emerged across age groups, income levels, history of being cheated on, history of being unfaithful, relationship type, and length.
The cause of the trend is “paternal uncertainty”, according to Frederick. Men can never know for certain whether their child is genetically related to them, since there is always a chance the child came from another father.
Yet, ironically, men are less likely to be faithful than women – a review of accounts from 16 societies within America found infidelity was the most common cause of marital dissolution, with 34 per cent of men and 24 per cent of women having been involved in extramarital sexual activities.
WOMEN MORE JEALOUS OF EMOTIONAL TIES
Women don't need to worry about whether the child they are raising is their own, which explains their slightly lower level of jealousy when it comes to sexual relationships. For them, the concern is more to do with allocation of resources and a man's investment in them as a mate.
As such, women are more likely to be jealous if their partner is emotionally close to another woman, irrelevant of whether that relationship is a sexual one. Such a bond might, in evolutionary terms, take key resources away.