Study: Finger length tied to sexual behavior

Scientists said on Wednesday they had amassed the first evidence to back theories that people fall into two broad categories - promiscuous or faithful - when it comes to sex.

Why humans seem to be an exception among mammals on the matter of sexual relationships has long been a puzzle.

Other mammalian species are emphatically polygamous or monogamous as a group. But as everyone knows, people do not fall into one neat category or the other. Everyone knows of couples that are sexually faithful, but also of men and women who are not cut out for monogamy.