Feet that stand test of time

As a paleoanthropologist and discoverer of Lucy (an extinct 3.9-million- to 3-million-year-old hominid species that is widely believed to be the ancestor of the genus Homo), I certainly enjoyed your article on the foot [“Such Power, Such Grace,” Jan. 1].

In 1975, I found a 3.2-million-year-old articulated foot near where Lucy was found. The important parts of the ankle were preserved and indicated that the shock-absorbing nature of the heel had already developed as well as the longitudinal and transverse shock-absorbing arches.

At that time, I cautioned all my jogging friends to cease running on pavement because it was clear to me that the foot had developed a unique anatomy in response to walking long distances on soft substrate such as grass and earth. Today, every one of those friends who had been beating the pavement has had a knee and/or hip replacement.

My only issue with the article is that the evidence for knuckle walking in Lucy’s forearm is not convincing. However, from an evolutionary perspective, it is likely that our ancestors did knuckle walk.

Genetic evidence shows that we are more closely related to chimps than to gorillas, and since chimps and gorillas are knuckle walkers (and this unique mode of locomotion is unlikely to have arisen twice), I think the common ancestor of chimps and humans (after the split from the gorilla) had to have been a knuckle walker.

Knuckle walking was therefore lost in the lineage that led to humans. Let’s see what older fossils eventually show us.

DON JOHANSON

Institute of Human Origins

Arizona State University

Tempe, Ariz.