New Delhi, Aug. 19: Women in the fertile phase of their ovulatory cycles experience greater sexual attraction to men other than their own partners, scientists exploring the genetics of infidelity have said.
In a new study, University of New Mexico scientists have confirmed their earlier findings that women’s sexual preferences change across ovulatory cycles, and produced data to show that genetic reasons might drive these preferences.
Their study, published in the Proceedings of the Royal Society, indicates that it is women’s evolution-driven search for “good genes” that motivates some women, when fertile, to get attracted to men who are not their own partners.
“Good genes are genes that promote the survival of offspring and attractiveness to the opposite sex,” said Randy Thornhill, a distinguished professor of biology at the University of New Mexico. “Some people have more good genes than others.”
The scientists used body asymmetry ' subtle differences in the sizes of ears, wrists, fingers and feet on the right and left side of the body ' among men as a marker for bad genes. “The more symmetric an individual, the more good genes,” Thornhill said. Relatively asymmetric partners have “bad genes”.
“It’s only when women are fertile in their cycle, and thus only when they can conceive, that their partners’ body asymmetry motivates them to pursue better genes,” Thornhill told The Telegraph.
“Such findings are hugely controversial. We can’t be sure they take into account cultural and environmental factors that affect human behaviour,” said Raghavendra Gadagkar, an evolutionary biologist at the Indian Institute of Science.
The study was based on questionnaires to 54 romantically involved heterosexual couples in the US. The women were between 18 and 44 years.
The scientists measured ear lengths and widths, wrist widths, ankle widths and finger lengths to assess asymmetry in their partners.
The researchers said that women’s attraction to men other than their primary partners probably leads to extramarital or extra-pair sex only occasionally. The costs associated with potential loss of the relationship are too high for women to act, Thornhill and his colleagues wrote in their paper.
Thus, satisfaction in relationships affects extra-pair attraction and actual infidelity, they said. Rates of extramarital or extra-pair sex vary across geography and cultures, with studies indicating a range of 1 per cent to 20 per cent.
“The 2 per cent to 20 per cent extra-pair paternity rate may partly be due to evolved adaptation for seeking good genes,” said Steven Gangestad, an evolutionary psychologist at the University of New Mexico and team member.
“But, no doubt, there are other reasons why women, and people in general, have affairs,” Gangestad said.
“Studies that investigate the biological basis of human behaviour are interesting, but their findings need to be taken with caution. They should never be a prescription for behaviour,” said Gadagkar, who has spent years studying the behaviour of insects.
Gadagkar said the concept of symmetry has been debated for years. “Yes, symmetry is difficult to maintain and it’s been associated with healthy genes. A breakdown of symmetry ' which might display itself as slight, yet measurable, differences in the sizes of ears, fingers or feet ' might occur due to mutations. “But the importance of asymmetry may be overestimated,” he said.