One key hallmark of being human is walking on two legs. It was a seismic shift seen in no other primates. Like much of evolution, it happened in fits and starts. The 4.4 million year-old Ardipithecus of Ethiopia was a tree climber with a grasping toe that would walk upright 3.2 million year old Lucy had a pelvis brought upright walking closer, with flaring hip blades for bipedal muscles.Some of that legacy remains in our closest relatives, the African apee, e.g. chimpanzees, bonobos, and gorillas, have upper hipbones (ilia) that are tall, narrow, and oriented flat front to back which anchor large muscles for climbing.