Superb New York Times science journalist Gina Kolata addresses a question that has bothered me for years. On sex surveys men typically report having twice as many sexual partners than women do. How is that possible? Kolata reports:
Everyone knows men are promiscuous by nature. It's part of the genetic strategy that evolved to help men spread their genes far and wide. The strategy is different for a woman, who must go through so much just to have a baby and then nurture it. She is genetically programmed to want just one man who will stick with her and help raise their children.
Surveys bear this out. In study after study and in country after country, men report more, often many more, sexual partners than women.
One survey, recently reported by the U.S. government, concluded that men had a median of seven female sex partners. Women had a median of four male sex partners. Another study, by British researchers, stated that men had 12.7 heterosexual partners in their lifetimes and women had 6.5.
But there is just one problem, mathematicians say. It is logically impossible for the mean number of partners for men to be different from the mean for women in any given population with equal numbers of heterosexual men and women….
One possibility is that the numbers could balance out if men frequently bought the services of prostitutes who are not generally included in sex surveys. However, I think it's far more likely that men and women both lie a lot about sex. Men who want to be seen as "studs" exaggerate, and women who want to avoid being regarded as "sluts" underestimate.
Whole Kolata article here.