Knees, Hips and Toes: A Runner Meets Australopithecus

From the Treadmill to the Anthropology Lab

1Yusra Halloran, a thirteen-year-old cross-country runner, spent a week in July at a running camp on a state university campus. After a long hill workout her right knee felt sore, so the camp's physical therapist, Beatriz Lindahl, watched her run on a treadmill. The soreness turned out to be tight muscles, not an injury. To explain the stretches she gave Yusra, Ms. Lindahl showed her a model of the human leg skeleton. The thigh bone slants inward from the hip to the knee. That slant keeps the knees and feet close under the body's center, so a person walking or running upright does not sway far to the side with each step.

2On the last day, the campers toured the university's anthropology lab, where Dr. Kenji Osei studies how the skeletons of humans and apes compare. His lab holds skeletons of a human, a chimpanzee and a gorilla, plus a cast of a famous partial skeleton of Australopithecus afarensis. It was found in Ethiopia in rock about 3.2 million years old (mya). No one has ever seen a living Australopithecus; everything known about it comes from its bones and footprints.

3Dr. Osei pointed out the large opening where the spinal cord leaves the skull. In humans the opening sits underneath the skull, so the head balances on top of an upright spine. Chimpanzees and gorillas usually walk on all fours, leaning on their knuckles, and in their skulls the opening sits farther toward the back. Their hip bones are tall and narrow, while human hip bones are short and wide. Apes also climb and hang from branches by their long arms. Their big toes stick out to the side and grip like thumbs, and their finger bones are long and curved.

4The Australopithecus cast mixes these features. Its hip bones are short and wide, and the top of its knee shows the thigh bone slanting inward. Its arms are long compared with its legs, and its finger bones are long and curved. Its brain was about 450 cm³. Footprints about 3.7 million years old, pressed into hardened volcanic ash in Tanzania, show a big toe lined up with the other toes, and most scientists think the same species made them.

5Before the tour ended, Dr. Osei added two more comparisons. Humans, chimpanzees and gorillas all lack a tail, while most monkeys have one. An ostrich also runs on two legs, but it has two toes on each foot, a beak, feathers and a skeleton built like those of other birds.