The emotional impulses also play a role in how aggressive they can become, he said. They directed the violence towards Andrew whom they feel was infringing on their territory.'Д¬himpanzees 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. 'This is why we come to the conclusion, as far as our expertise goes, that it was a territorial defense. 'They have no anger,' Cussons said of the chimps. 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. 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. Such physical lack of control can potentially lead some chimps to become more aggressive when physical. 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. In chimps, the muscle fibers closest to the bones - those deemed to be the source of strength of both chimps and humans вЂ“ 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.ДЄlso, unlike humans, chimpanzees have less control over their muscles. Research suggests the difference in strength between the two lies in the muscle performance.

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.

Chimpanzee muscle