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Handshake: Window on Your Genes?

A limp handshake might say more about a man than he'd like to admit. According to new research, a firm grip is an indicator of genetic fitness. The findings link grip strength to aggressive behavior and sexual history and might provide insight into the mindsets of bullies.

Hand grip strength (HGS) is an inherited trait; about 65% of a person's grip strength is genetically determined, whereas the remaining 35% depends on training and developmental factors such as nutrition. Past studies have connected HGS to various measures of physical condition, including bone density and longevity. "It's a ubiquitous measure of health and vitality," says evolutionary psychologist Gordon Gallup of the University at Albany in New York state.

To find out whether HGS also reflects sexual and social behaviors, Gallup and his colleagues recruited 143 undergraduates from the university. The team measured their grip strength and anatomical variables linked to attractiveness--shoulder-to-hip ratio for men and waist-to-hip ratio for women. Each participant also completed a survey about sexual history (including age at first sexual encounter and number of partners) and middle and high school bullying behaviors.

The female participants showed no correlations between HGS and sexual history or social behaviors, the team reports in this month's issue of Evolution and Human Behavior. But men with high HGS started having sex sooner, reported more sexual partners, and were more aggressive during high school (although not middle school). According to Gallup, asserting dominance over others and mating early and often are attributes that help pass along one's genes. "Our conclusion is that hand-grip strength is an honest indicator of fitness," he says, adding that whereas HGS is related to overall muscularity, the latter is "nowhere near” as closely linked to health as is HGS.

Other experts have varying takes on the results. Evolutionary psychologist John T. Manning of the University of Central Lancashire in the United Kingdom frets that the study did not control for the ethnicity of the participants; racial differences in average size could make the trends weaker or stronger in other sample groups. (According to Gallup, university regulations prohibit asking about race, even anonymously.)

Evolutionary psychologist Bill von Hippel of the University of Queensland in St. Lucia, Australia, says that the most exciting finding is the bullying link. Bullying is seen as "a product of low self-esteem and self-doubt," says von Hippel. These data suggest that, instead, it's a method of jockeying for status, chosen by strong men who excel at it.