updated 7/11/2012 8:17:46 AM ET 2012-07-11T12:17:46

Chimpanzees have made headlines in recent years for several unprovoked attacks against humans, the latest last week at the Jane Goodall Institute Chimpanzee Eden in South Africa. The severely injured victim, University of Texas graduate student Andrew Oberle, remains in intensive care.

Oberle was mauled by chimpanzees as he gave a lecture to about a dozen tourists. The brutal attack prompted many to wonder what, if anything, provoked the animals? Experts suggest that multiple reasons could explain the attack.

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Eugene Cussons, managing director of the sanctuary and host of the Animal Planet show Escape to Chimp Eden, said Oberle received training prior to the incident, but broke the rules when he went through two fences separating the primates from humans. A male chimpanzee grabbed Oberle and pulled him under one of the fences, which was electrified.

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Aside from that dangerous misstep, the fact that the attackers were male is not surprising to those who study chimpanzees. Sylvia Amsler, a lecturer in the Anthropology Program at the University of Arkansas at Little Rock, told Discovery News that male chimps in the wild commonly engage in war-like behavior to defend or acquire territory.

“Such attacks can be severe and fatal,” she said. “In the case of an adult victim, the attacking males take turns beating and jumping on the victim. Attackers use their canines to bite and tear at the victim, so that any body parts that stick out, such as testes and ears, are often ripped off during an attack.”

Jenny Short, assistant director of colony management and research services at the California National Primate Research Center, reminded that chimpanzees and other primates are not domesticated animals.

“You have to be reactive and extremely careful around them,” she told Discovery News. “We work with rhesus macaques, which are much smaller than chimpanzees, and even they require strict precautions. If you go to a zoo and look at chimps, it takes your breath away because they are so big and strong.”

Paleoanthropologist Alan Walker of Penn State University thinks that even if a human and a chimp were somehow evenly matched in size, chimpanzees wind up using all of their muscle strength, whereas humans tend to hold back.

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Relative to body mass, chimpanzees have less grey matter in their spinal cords than humans have. This matter contains large numbers of nerve cells that connect to muscle fibers and regulate muscle movement.

The finely tuned motor system in humans gives us the ability to do things like make complex tools, throw accurately, and manipulate small objects. Conversely, when a chimp uses its muscles, particularly in a defense or attack mode, the action is more “all or nothing,” with each neuron triggering a higher number of muscle fibers, Walker explained.

“That is the reason apes seem so strong relative to humans,” he added.

Yet another possible factor in the Chimp Eden attack is that the primates housed there were rescued from the illegal pet and bushmeat trades, as well as from the entertainment industry. In short, these primates were previously abused by humans and might be more inclined to become defensive.

The sanctuary, near the city of Nelspruit, has been a member of the Pan African Sanctuary Alliance (PASA), a group of 21 primate sanctuaries across Africa, since 2000. David Oosthuizen, executive director of Chimp Eden, said that over those 12 years, the sanctuary has maintained the standards of care, safety and conservation required to be part of the PASA.

Oosthuizen said, “We have never had an incident like this and we have closed the sanctuary to investigate how we can try to ensure it will not happen again.”

© 2012 Discovery Channel


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