Bipedalism, the type of locomotion where an animal walks on only two legs, is uniquely evolved in the human ancestral lineage. While some other animals can walk on their hind limbs for short distances, humans are the only living creatures who are obligate bipeds. Our earliest evidence for bipedalism comes from the fossil species Sahelanthropus tchadensis, which lived 7.0 to 6.0 million years ago. Evidence from the fossil record suggests that the earliest hominins were at least partially bipedal, meaning they were able, and tended, to move around on two legs. The base of preserve fossil skulls show that their heads were positioned on top of their spines suggesting these creatures had more upright bodies. There is also an upper leg bone from around 6.0 million years ago that seems adapted to bipedal locomotion. These fossils show that changes in locomotion preceded enlargement of the brain.

Image credit Shutterstock.