Chimpanzees vs. Humans: Sizing Up Their Strength

July 2, 2012 — -- The mauling of Texas graduate student Andrew Oberle by two chimpanzees at the Jane Goodall Institute Chimpanzee Eden in South Africa Thursday was a reminder that in strength, size might not matter.

Chimpanzees are considered the closest living relative of humans, sharing 95 to 98 percent of the same DNA, according to the Jane Goodall Institute in Washington, D.C., a separate entity from the facility in South Africa.

But in no way do humans compare with a chimps' sheer strength and the few percentage points in which the two differ are extreme, many experts say.

"It's the closest thing we know to human warfare" when a chimp is provoked, said Steve Ross, director of the Lester E. Fisher Center for the Study of Conservation of Apes at Lincoln Park Zoo in Chicago.

"Chimps are incredibly strong and fast so humans are easily overpowered."

Indeed, chimpanzees have been shown to be about four times as strong as humans comparable in size, according to evolutionary biologist Alan Walker, formerly of Pennsylvania State University.

Research suggests the difference in strength between the two lies in the muscle performance.

In chimps, the muscle fibers closest to the bones -- those deemed to be the source of strength of both chimps and humans – are much longer and more dense, so a chimp is able to generate more power using the same range of motion, Ross of the Lester Fisher Center said.

Also, unlike humans, chimpanzees have less control over their muscles. As a result, sometimes chimps use more of their muscle strength than necessary, according to Walker's theory, published 2009 in the journal Current Anthropology.

Such physical lack of control can potentially lead some chimps to become more aggressive when physical. In Thursday's case, however, an internal investigation by the Jane Goodall Institute near Johannesburg showed that the chimps might not have intended to be malicious, Eugene Cussons, director of the institute, told "Good Morning America" today.

The two chimps saw Oberle's crossing the fence into the chimps' space as a violation of their territory, prompting them to take action, Cussons said.

"They have no anger," Cussons said of the chimps. "This is why we come to the conclusion, as far as our expertise goes, that it was a territorial defense. They directed the violence towards Andrew whom they feel was infringing on their territory."

Chimpanzees have a wide range of emotions and they are similar to what humans experience, yet they are known to have erratic and unpredictable impulses, Ross said. The emotional impulses also play a role in how aggressive they can become, he said.

"They can adapt very well to their environment but that doesn't preclude that they are territorial and they are violent and wild animals first," Ross said. "There's an aggression toward individuals that are not in their group."

But chimps are often seen as friendly and cute animals because many facilities use preventive measures to prevent the aggression, he said.

Indeed, the same muscles that are considered to be the source of a chimp's strength can also be seen as a detriment for the animal.

The lengthy muscle fibers mean chimps and other great apes can't swim, Ross said. To protect humans, many zoos create water barriers around the chimps' area so they cannot physically approach, Ross said.

While chimps are most often seen in a zoo environment or in facilities working hand in hand with humans, they are inherently wild and aggressive animals so both trained and untrained individuals should never let their guard down, he added.

"There's never a safe time to be in the same place as a chimp," Ross said. "The natural tendency of chimpanzees is one of aggression and there's always a need among them to demonstrate power and territory."