Less time with partner, more interest in sex

When it comes to relationships, perhaps absence does make the heart grow fonder. According to researchers, the less time a man spends with his female partner after having sex, the more attractive he finds her--and the greater his interest in having sex with her again. This phenomenon may arise from an evolutionary strategy known as "sperm competition," according to Todd K. Shackelford, an assistant professor of psychology in the College of Liberal Arts at Florida Atlantic University.

"The bottom line here is that we find (this) effect for men but not for women," he said. Shackelford and his colleagues presented the findings at the 107th Annual Convention of the American Psychological Association.

While the investigators have since expanded their study to include over 2,000 subjects, the initial data was based on assessing the behavior of 304 German and American heterosexual men between 17 and 71 years of age. All the men were in committed sexual relationships lasting anywhere from 1 month to 38 years.

The researchers presented the subjects with a questionnaire, in which they were asked how many hours had passed since their last intercourse with their partner, how many hours they had spent with their partner since last intercourse, and feelings of attraction towards their partner.

The team found that the less time the men spent with their partner in the interval since their last encounter, the more attractive he found her and the greater his interest in sex. Shackelford and colleagues conclude that it is not simply a question of sexual frustration or a pent-up drive for sex that motivates the man's urges and feelings of attraction since their last encounter.

Shackelford's team believes this behavior may be rooted in a biological concept called "sperm competition." Studied for over 30 years among birds, insects and nonhuman primates, this evolutionary theory poses that sperm competition occurs when the sperm of two or more males simultaneously occupy the reproductive tract of the female and must compete to fertilize the egg.