Finger Symmetry Indicates Fertility

Judy T. Greenberg ’07 said she once had a crush on a boy with “massively asymmetrical” thumbs, breaking with conventional wisdom that symmetry is beauty. But a new study by Radcliffe fellow Grazyna Jasienska goes one step further, linking hand symmetry in women not only to beauty—but to greater fertility.

“Evolutionarily speaking, when it comes to the...selection of female partners, the most important thing is fertility,” said Jasienska, of Harvard’s Radcliffe Institute for Advanced Study.

Jasienska and her team tested 171 urban and rural Polish women during their menstrual cycle, according to the study. Women with up to a 1 millimeter difference in length between the second and fourth digits of their hands were considered symmetrical, and the rest were dubbed asymmetrical.

Researchers then took daily saliva samples from the women to measure their levels of estradiol, a female fertility hormone that increases the chances of pregnancy, she said.

Researchers found that the levels of the fertility hormone in symmetrical women were 13 percent higher than asymmetrical woman over the entire menstruation cycle, and levels were 28 percent higher at mid-cycle for symmetrical women.

A 30 percent increase in estradiol levels increases a woman’s likelihood to get pregnant threefold, Jasienska said.

“Humans are very sensitive to symmetry in general,” she said. “Some researchers show that babies just a few days old are able to distinguish symmetrical and asymmetrical faces.”

Greenberg, a Studies of Women, Gender, and Sexuality concentrator, said that although facial symmetry does imply consistency in genes and better genes for the future, hand symmetry is not necessarily a reliable marker.

Jansienska said that she used hand symmetry because it is probably correlated to facial symmetry.

“This study is something which, to some extent, explains our sensitivity to detecting symmetry,” she said, “because maybe it is a biomarker of fertility.”