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."... Larger primates, such as humans and chimps, live in groups and adopted the strategy of aggressively defending themselves against threats, which usually works against predators, Hawks said. Being social has therefore helped keep us safe, along with the benefits of bipedalism.