UCSB Study Examines Human Perception of Strength

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A team of UCSB scientists found that a mechanism exists within the human brain that enables a person to determine — with a substantial amount of accuracy — the fighting capabilities in men's upper bodies simply by looking at them.

The study — conducted by four UCSB faculty researchers led by Dr. Aaron Sell of the UCSB Center for Evolutionary Psychology — also found that the assessment can be made even when “everything but the men’s faces” are obscured from the assessor’s view. Research for the study was a joint effort between Sell and UCSB professors Leda Cosmides of the psychology department, and John Tooby and Michael Gurven, from the anthropology department.

Sell, who is a postdoctoral fellow at UCSB, said in an October 22 university press release that the ability to “hone in” on fighting capabilities was a very important function for early humans and played a role in their evolution.

“Assessing fighting ability was important for our ancestors, and the characteristic that the mind implicitly equates with fighting ability is upper body strength,” Sell said in the press release. “That’s the component of strength that’s most relevant to pre-modern combat. The visual assessment of fighting ability is almost perfectly correlated with the perception of strength, and both closely track actual upper body strength.”

“What is a bit spooky,” he continued, “Is that upper body strength can even be read on a person’s face.”

When conducting the study, the researchers asked test subjects to assess the physical strength of a few individuals based on photographs of their faces, their bodies, or both — and then assign a ranking to their strength, and also to their fighting ability, on a scale from one to seven. The researchers then compared these numbers to see if there was any correlation between the two perceived abilities. Some of the photographs depicted men whose capabilities for physical strength was suggested in the image in some way—like a photograph of a man shown using a weight-lifting machine. Researchers found that when presented with this type of photograph, a respondent’s perceptions of the man’s strength were highly correlated with their perceptions of his ability to fight. (“When you see that kind of correlation it’s telling you you’re measuring the same underlying variable,” Tooby noted in the press release.)

The study also found that perceptions of strength and fighting ability tended to reflect the men in the photographs’ actual strength and fighting abilities, as measured on weight-lifting machines at a gym.

But, less predictably, the researchers found later on in the study that this extended far beyond the gym: Both men and women were found to have the ability to accurately judge men’s strength even in a cross-cultural context, according to the press release—“whether those men are drawn from a general campus population, a hunter-horticulturalist group in Bolivia, or a group of herder-horticulturalists living in the Argentinian Andes,” the respondents were able to accurately gauge the men’s individual strength.

Perhaps the study’s most important finding was that relating to upper-body strength — namely, the upper body's appearance can give information about a man’s strength. When researchers measured perceptions of upper-body strength side-by-side with those of lower body strength in test sample populations from both the United States and Bolivia, the results showed that perceptions of men’s strength and fighting ability reflect considerations of upper body strength, and not that of their legs. Tooby added that whether people are assessing toughness or strength, they always implicitly register upper body strength rather than lower, because “that’s the critical information our ancestors needed in deciding — or feeling — whether to surrender a disputed resource or escalate aggressively.”

It was the results from this portion of the study that led the researchers to suggest that the ability to judge physical strength and fighting ability is from a mechanism in the brain — one that serves “different, but equally important” purposes for men and women. In men, the researchers said in the press release, this mechanism can be described as a dual-purpose “barometer,” used to measure potential threats and to help determine what level of aggression or submission to express when facing a potential enemy. The brain mechanism in women, however, “helps identify males who can adequately protect them and their children.”

Sell said there is much more research to be done on the findings of his study. Now that his team has discovered that the body receives the fighting signal, they hope to find out how the body actually makes it.

”The next step is to isolate what it is in the face that indicates upper body strength,” said Sell. He suggests that the correlation may lie in the heavier brow ridge and thicker jaw that result from increased levels of testosterone.

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