Bipedalism—walking on two feet—is a hominid adaptation which first turns up in the fossil record about six million years ago. Bipedalism can be seen as a specialization: our earliest hominid ancestors were able to propel themselves forward in a variety of ways, using their hands and feet both as grabbers to get through trees or walk upright as circumstances dictated. We modern types evolved out of most of those abilities. The evolution of human feet as sole support of our bodies was a fairly slow process.
Modern feet, compared to those of our earlier ancestors, have short toes, a high arch, a big toe (hallux) that is in alignment with our other toes, and a robust flat heel. Humans walk in a rolling heel-ball-toe movement; pre-humans and African apes plant heel and ball together and then toes. They pick up their feet in a variety of ways, but generally with comparatively little pressure on their toes; and their big toe is widely splayed out.
More on Ancient Feet and Shoes
Bennett, Matthew R., et al. 2009 Early Hominin Foot Morphology Based on 1.5-Million-Year-Old Footprints from Ileret, Kenya. Science 323:1197-1201.
