How human feet compare to ape feet

At this station, you’ll find some articulated human feet. “Articulated” means that the bones are assembled together at their joints – two bones that articulate with each other are connected at a joint.

You will also find some feet from two living species of great apes, gorillas and orangutans. These feet are obviously different from human feet in several respects. Most obviously, ape feet have an opposable first toe. The first toe in humans is often called the “big toe” or “great toe”, but in these apes it is quite a bit shorter than the other toes. In anatomical terms, the first toe is called the hallux, and it is on the medial side of the foot, the one closest to the midline of the body.

The other toes, which are lateral to the hallux, are substantially longer in apes than in humans. Each of these toes consists of three bones, which are called phalanges. The closest to the rest of the foot is the proximal phalanx, the furthest is the distal phalanx. The one in the middle of the toe is called the intermediate phalanx.

Take a look at the intermediate phalanges in the human and ape feet. What do you notice about them? This is a substantial difference in the anatomy of human and ape feet, as human toes have greatly reduced all the phalanges but particularly the intermediate ones.

Think of a hypothesis to account for the shorter toes in humans. Why would it make a difference how long the lateral toes are?