For the study, the researchers created a database of photos of shirtless or tank-top wearing men, with their faces obscured. All of the men were university students, but 60 were recruited from the gym while 130 were just normal psychology students. All the men were also given tests with weights, to quantify their physical strength.
Women and men were then asked to judge how strong they thought the men were, on a scale of 1 to 7, based on the images. Their guesses were strikingly accurate, correlating well with the strength tests. Furthermore, the women's ratings of the men's attractiveness correlated directly to their physical strength.
"No one will be surprised by the idea that strong men are more attractive," Aaron Lukaszewski, an evolutionary psychologist at California State University at Fullerton and an author of the study, told The Washington Post. "It's no secret that women like strong, muscular guys."
However, the researchers were less interested in ascertaining the obvious, and more interested in discovering.
"People are going to wonder why scientists needed to study it," Holly Dunsworth, an anthropologist at the University of Rhode Island who was not involved in the research, said. "The answer would be because they want to know how these preferences evolved."
The researchers point to "ancestral cues," an evolutionary relic of ancient human mating rituals. Ancient women would instinctually have chosen men who were better able to provide for and protect them and their families. It's only natural to assume bigger and stronger men would do this more adequately.
But when it comes to male attractiveness, a popular theory says that there's a "sweet spot" for brawn. Beyond a certain point, too much muscle and strength becomes unattractive. This new study seems to prove the opposite.
"The theory is that, yes, there would have been benefits ancestrally, in terms of the ability to acquire resources, protecting offspring, hunting and so on. But at a certain point, mating with highly dominant men, they can exert all this aggressive coercive control and there might be costs," Lukaszewski explained, pointing out that his study shows that women prefer brawnier guys, regardless of the potential downsides.
Even if strength is the key factor that attracts women to men, the research also suggest it's not all about perfect physique and chiseled muscles.
"Our results suggest that even if you're a bit overweight, looking strong can buffer that. Basically, being a strong, fat guy is OK, which I think would bring comfort to many," Lukaszewski said.
Despite the findings, less muscular men shouldn't feel too disheartened.
As The Independent points out, several other scientific studies have noted a variety of factors that women apparently find more attractive. Among other things, previous research has shown that women find bald and short men more attractive than their counterparts.