Quoted: There are a few likely reasons why they don’t attack more often. Looking at our physiology, humans evolved to be bipedal — going from moving with all four limbs to walking upright on longer legs, according to John Hawks, a paleoanthropologist at the University of Wisconsin-Madison.
“There is a threat level that comes from being bipedal,” Hawks told Live Science. “And when we look at other primates — chimpanzees, gorillas, for instance — they stand to express threats. Becoming larger in appearance is threatening, and that is a really easy way of communicating to predators that you are trouble.”