The human family, or Hominidae, evolved in Africa and diverged from the ape line some 5-6 million years ago. The primary characteristic of Hominids is bipedalism, or the ability to walk on two legs. An increase in brain size, or encephalization, is another clinal characteristic as well. There are several candidates for our earliest, bipedal ancestor. Ardipithecus ramdus is the most likely candidate, although Orrorin and Sahelpithecus have been floated as ancestor of the Hominid line. Ardipithecus photos are shown below.