If you're thinking about challenging a guy to a fight, listen to his voice first. Researchers on three continents have found that the male voice contains cues about upper body strength, a key factor in determining whether a potential opponent is a strong fighter or a wimp.
The findings are part of an ambitious ongoing research project at the Center for Evolutionary Psychology at the University of California, Santa Barbara. They suggest that early humans made good use of several cues, including what they could see with their eyes -- and now voices -- to size up the competition.
Significantly, the findings were about the same in four different cultures, and four different languages, showing that the ability to detect physical strength in a man's voice is evolutionarily based, not culturally produced.
Strength is detected in the male voice, but not the voice of a female, and that's also evolutionarily based. Early man was the hunter, warrior, and protector, while early woman minded the hearth and raised the kids, according to Aaron Sell, lead author of a report on the research in the Proceedings of the Royal Society B.
On the surface, there's nothing in the male voice that should reveal physical strength. The "usual suspects," as Sell put it, like pitch, are unlikely candidates. Pitch is controlled by the vocal chords, not upper-body muscles.
Sell and his colleagues, including Leda Cosmides and John Tooby, co-directors of the center, have delved deeply into how early man evaluated the formidability of a rival. Previous research showed that visual cues carried important information about the competition, which may not be that surprising given the fact that a wise man doesn't go to muscle beach to pick a fight. All he has to do is open his eyes to know that's not a good idea.
But there are times when the opponent might not be visible. Either he's too far away, or its dark outside, or he's hiding behind a bush, or he's on the phone. So is it possible that just his voice could tell whether fight or flight is the better option?
"We found that subjects accurately assessed upper-body strength in voices taken from eight samples across four distinct populations and language groups: the Tsimane of Bolivia, Andean herder-horticulturalists (in Argentina) and United States and Romanian college students," the study concluded.
The researchers expected that result, because they hypothesized that the clues carried in a male voice were a product of evolution, and thus should be universal, but even they were surprised at how easy it is to find a strong man among the weak just by how he sounds.
Sell said in a telephone interview that he was skeptical when he heard the first batch of recorded voices from the 49 Tsimane hunters and farmers in Bolivia who participated in the study. They were also tested for strength, as were all the participants.
Their language is "just so different from English," he said. "They have this really weird nasal quality," and he wondered if he could detect strength from any of the recordings. So he put them in his computer "and played them back to see if I could actually assess strength. I was certain I was getting nowhere when I was listening to them, but in the end my rating worked out just fine."