Biology, not heart, provokes infidelity

Sydney Morning Herald, Sydney, Australia, Deborah Smith, Science Editor, January 15, 2009

BEAUTIFUL women who have affairs can now blame it on their sex hormones.

Women with higher levels of oestradiol, a form of oestrogen, not only look and feel more attractive, they are also more likely to cheat on their partners, a new study has found.

One-night-stands are not what interest these flirtatious females, who tend to have bigger breasts, relatively small waists and symmetrical faces as a result of their high levels of oestradiol.

Rather, they adopt a strategy of serial monogamy, say the researchers, led by Kristina Durante of the University of Texas.

"Without necessarily being consciously aware of their motives, highly attractive women are probably able to capitalise on their desirability and continually acquire a higher-quality long-term mate by trading up when the opportunity arises," said Dr Durante.

A James Cook University psychologist, Frances Quirk, said Marilyn Monroe, with her hourglass figure, was a classic example of a high-oestradiol female. "And her relationship history is a fairly good match," she said, noting the actress's marriages and affairs with increasingly important men.

Associate Professor Quirk said the study added to other evidence that hormones such as testosterone and oxytocin influenced the sexual and social behaviour of men and women. "The bottom line is that we are driven by our biology a lot of the time."

Dr Durante's team tested the level of oestradiol, which is linked to fertility, in the blood of 52 women aged between 17 and 30.

Those with higher levels rated themselves as more desirable than average, and were judged to be significantly more attractive by others. They had had more long-term relationships than those with lower levels of the hormone, and "reported a greater likelihood of flirting, kissing and having a serious affair with someone other than their primary partner", Dr Durante said.

The results were consistent with the possibility that "highly fertile women are not easily satisfied by their long-term partners and are especially motivated to become acquainted with other, presumably more desirable, men", she said. "Importantly, such motivations do not seem to stem from a greater interest in casual sex."