London, Oct 9 (IANS): Men are most jealous of sexual infidelity but when it comes to women, emotional infidelity is what makes them the most jealous, reveals a study.

If your partner has sex with someone else, it is considered infidelity even if no emotions are involved.

But it is also considered infidelity when your significant other develops a close personal relationship with someone else, even if there is no sex or physical intimacy involved.

Norwegian researchers now show that men and women react differently to various types of infidelity and evolutionary psychology may help explain why this may be.

“Men and women's psychology is similar in most areas -- but not when it comes to reproduction," said associate professor Mons Bendixen from the Norwegian University of Science and Technology's (NTNU).

Although the evolutionary psychologists had expected women and men to respond differently to questions about infidelity and jealousy, they were surprised that the differences were so strong.

Recent research on jealousy considers two main types of infidelity: Having sex with a person outside the relationship, or developing an emotional attachment to a person outside the relationship.

In the recent study, over 1,000 participants were randomly given one of four versions of a questionnaire about jealousy.

'We found clear sex differences in the jealousy responses among those who had to choose which aspect of infidelity was most upsetting to them,” the authors noted.

The evolutionary perspective is different. According to this approach, men and women over thousands of generations have had to adapt to different challenges that are related to reproduction.

Infidelity is one such challenge.

According to the evolutionary psychology explanation, men's jealousy is an emotional reaction to signs of sexual infidelity. The jealousy serves to reduce the chances that his partner is cheating, since he then monitors her more closely.

“Women today are descendants of women who over thousands of generations have reacted with jealousy to men who sent signals that they were less invested in them,” the authors noted.

Evolutionary psychologists believe that women are especially sensitive to signs that the man is devoting time and attention to other women.

The findings were published in the journal Personality and Individual Differences.