The finding, by PhD student David Frederick and associate professor Martie Haselton, stemmed in part from a study of 99 UCLA undergraduates of varying brawniness. As described in a news release about the paper (entitled "Lift more weights, find more mates"), the undergrads were photographed and then rated for muscularity on a 9-point scale, where nine was the most muscular and one was the least.
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Other studies by the UCLA duo (published together in the latest issue of the Personality and Social Psychology Bulletin) found that men who rated themselves as being above-average muscular also were more promiscuous and more likely to have had short-term flings, including ones with women who had boyfriends.
To evolutionary psychologists Frederick and Haselton, this all adds up to a pattern: Muscularity is a sexual attention-getter akin to that show-off peacock's tail. But both peacock tail and muscles have their downside, and in the latter case, Frederick says, it's that the muscle-building hormone testosterone is associated with suppression of the immune system.
Thus, Frederick says, muscles are "indicators of mate quality" because — like that preposterous tail — they "demonstrate an ability to flourish in the face of what's really a drag on the system."
"If you're trying to figure out why men — especially young men — spend so much time at the gym, here's your answer," he said.
A postscript to the body builders: Women don't seem to like extremes. When asked to rate six silhouettes of men with different degrees of brawn, women rated the in-between "toned" men as most sexually attractive — and also more sexually trustworthy.
— Rosie Mestel