<lion roar sound>

The animal kingdom is full of species that use sound—growls and bellows and roars—to signal size. Dogs do it. <dog growls> Red deer do it. <red deer roar> Koalas do it. <koala rumble>

But now we can add humans to that list. <human roar> Because a new study suggests we can size up other people by the sound of their roar alone.

First, researchers took the circumference of 61 men's and women's biceps, measured their grip strength, and their height. Then they told 'em to let loose a roar. <roar>

"I would probably describe it as the most hellish version of Groundhog Day you can think of." Jordan Raine, a behavioral ethologist at the University of Sussex. "If you just imagine 30 actors in training coming into a small room one after another and roaring at you, um, yeah it was an experience, that's for sure." 

His team then played those roars back to a separate group of male and female listeners, who'd also been measured for strength and size. They found that men correctly rated other men as substantially stronger than them 90 percent of the time, based on roar alone. 

Men did tend to underestimate women's strength by the sound of their roars, <woman's roar> and women overestimated men's strength. But, in general, roaring like a wild animal seemed like a pretty accurate way to telegraph body size and strength.

The researchers also found that regular shouting <shouting sample> did not seem to have the same effect as a roar. "So what the roaring is actually doing is having this exaggerating effect on strength, which is very similar to the adaptations that non-human mammals possess that allow them to exaggerate their strength as well." The full results—and more roars—are in the journal iScience. [Jordan Raine et al., Human Listeners Can Accurately Judge Strength and Height Relative to Self from Aggressive Roars and Speech]

The finding could have practical, real-world applications too. For example, soldiers have roared in battle throughout history to attempt to intimidate the enemy. "And the U.S. National Park Service actually recommends roaring as a defense strategy against bears."

Just hope that the bears' hearing is better than their eyesight. 

—Christopher Intagliata 

[The above text is a transcript of this podcast.]