Heading For Muscle Beach? Check Out the Voices

June 23, 2010 — -- 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.

Findings True Across Three Continents

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."

He nailed it, even though he doesn't speak the language and couldn't understand the words that the participants had been given to speak. So he retested the Tsimane as they spoke only vowels. Again, he could tell which voices revealed strength.

What he can't tell us, however, is how. "It's not pitch, not amplitude, not volume, it's not how fast you are talking," he said. "It's one of those mysteries. We really don't know."

Although the study was aimed at our ancestors, it's still relevant today. In an earlier study, Sell found that "stronger males are also rated as more physically attractive, have more sexual partners and lose their virginity at earlier ages than weaker men."

Other studies have shown that upper-body strength is the most important factor in hand-to-hand combat. Weight and height are less important in a fighter, and interestingly, the participants in the study couldn't accurately judge either weight or height by the voice. Strength is what really matters in a fight. For a wimp, the ability to beat a hasty retreat is probably more important.

Some 360 persons, including 20 herders from villages in Argentina, took part in the study. Voice samples, and body and strength measurements, were taken from the eight populations. The participants were all males except for 80 females at UCSB and the University of Timisoara in Romania. Key findings:

Estimates of strength from the voice were "accurate and highly significant across all six male samples." The accuracy was similar to the accuracy of assessments from a visual image of the face in earlier studies, but lower than estimates from images of the body.

They found the same level of accuracy regardless of language or culture.

The accuracy in determining strength from a woman's voice was about half the accuracy as from a man's voice.

Voice and visual images enhance each other, so if you want to fight, look and listen.

Some might question the value of devoting so much time and energy to studying how ancient man sized up his opponent. If we really want to understand how the human brain works today, we better understand how it got to where it is now, Sells said.

"We're documenting how natural selection has designed the mind," he said. "The big question in evolutionary psychology is whether or not natural selection is important to understand if you want to understand human behavior. We're arguing that's the process that built the mind, so if you want to know how the mind works you're really hamstringing yourself if you don't study natural selection."

This research adds a new chapter to that debate. Our ancestors learned how to read a man's voice. We can still do that today.

The next big question on Sell's plate is to answer this basic question:

How do we do it?