"To a woman the first kiss is just the end of the beginning; to a man it's the beginning of the end." —Helen Rowland
Try to imagine that your loved one has become romantically interested in someone else. And then try to envision which scenario would bother you more: (a) learning that your partner has fallen in love with that person or (b) discovering that your partner has had meaningless sex with that person. Obviously, both situations are painful to think about, but chances are one of these bothers you more than the other. And just as likely, your gender has a lot to do with which one causes you the most anguish.
Both men and women experience jealousy and according to David Buss, Ph.D., professor of evolutionary psychology at the University of Texas, this is both healthy and necessary to the fitness of a faithful relationship. In The Dangerous Passion: Why Jealousy Is As Necessary As Love and Sex," Buss describes his survey of women and men in the United States, the Netherlands, Germany, Japan, Korea and Zimbabwe. The majority of women interviewed were troubled more about a partner's emotional infidelity, while the men were most upset about sexual transgressions.
The differing grounds for jealousy between men and women reveal highly adaptive responses for the human species. Since fertilization takes place inside the female body, it is difficult to determine paternity with any real certainty. The ancestral man was therefore unable to know whether he was, in fact, the real father of his children.