Having exactly 5 toes would appear to be unimportant for running/walking, as shown by a large number of animals which don't have 5 toes. However, the human is pretty unique in its upright stance, so perhaps the jury is still out. There is a huge amount of interest currently in the evolution of human feet in the context of "barefoot running", as evidenced by the best-selling book "Born to Run". Based on the work by Daniel Lieberman at Harvard, the view of the human foot as a compromise forced by the descent from trees is being revised, and the newer view is that the present human foot is an exquisite result of upwards of 10 million years of evolution to adapt to long runs & long walks (perhaps averaging >20 miles per day). A side-effect of this research is the conclusion that -- for running on natural surfaces at least -- wearing shoes (particularly shoes with a built-up heel) is actually counterproductive & leads to poor running style & lots of injuries. http://www.barefootrunning.fas.harvard.edu/ Unlike many hoofed (hooved?) animals, humans have very sensitive feet, which enables them to instantaneously react to surface conditions while running. This is particularly important for bipedal locomotion, since humans don't have an extra set of legs to "fall back on" and the alternative to instantaneous reaction may be a face-plant. I've watched movies of horses & mules walking on narrow paths with treacherous footing, and these animals tend to rely on their extra feet to overcome a stumble. Separated toes appear not to be particularly useful for running/walking, and make them more prone to injury & frostbite (a relatively recent problem arising after leaving Africa). A comparison of chimp toes & human toes show the loss of individual grasping ability of human toes. Chimps & gorillas, on the other hand (pun intended), can't run/walk for long distances upright & utilize their longer arms to help in locomotion. However, as walking robots become more & more common, roboticists are learning more & more about the why's and how's of leg, ankle & foot design, and they may yet shed some light on the function of toes. At 06:35 PM 12/20/2010, Bill Gosper wrote:

5. The detailed topological equivalence yet functional inequivalence of hands and feet needs to be explained. The present design of toes as ridiculous parodies of fingers, right down to fourteen phalanges and nails, confers no advantage over a simple flexible tab, like being born with socks on. (Except for people without hands.)