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 is genetically programmed to want just one man who will stick with her and help raise their children.

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 US 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 heterosexual men to have more partners on average than heterosexual women. Those survey results cannot be correct.

It's about time for mathematicians to set the record straight, says Dr David Gale, an emeritus professor of mathematics at the University of California, Berkeley.

He provides a “theorem”, writing in an e-mail message: "We suppose that on the day after prom, each girl is asked to give the number of boys she danced with. These numbers are then added up, giving a number G. The same information is then obtained from the boys, giving a number B. Theorem: G(EQUAL)B. Proof: Both G and B are equal to C, the number of couples who danced together at the prom. QED."

Sex survey researchers say they know that Gale is correct. Men and women in a population must have roughly equal numbers of partners. So what is going on and what is to be believed?

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