Footprints to Fill


Flat feet and doubts about makers of the Laetoli tracks
By Kate Wong

It is one of the most evocative traces of humanity's ancestors ever found, a trail of footprints pressed into new fallen volcanic ash some 3.6 million years ago in what is now Laetoli, Tanzania. Discovered in 1978 by a team headed by Mary Leakey, the Laetoli footprints led to the stunning revelation that humans walked upright well before they made stone tools or evolved large brains. They also engendered controversy: scientists have debated everything from how many individuals made the prints to how best to protect them for posterity. Experts have generally come to agree, however, that the tracks probably belong to members of the species Australopithecus afarensis, the hominid most famously represented by the Lucy fossil. Now new research is calling even that conclusion into question.

The case for A. afarensis as the Laetoli trailblazer hinges on the fact that fossils of the species are known from the site and that the only available reconstruction of what this hominid's foot looked like is compatible with the morphology evident in the footprints. But in a presentation given at the American Association of Physical Anthropologists meeting in April, William E. H. Harcourt-Smith of the American Museum of Natural History and Charles E. Hilton of Western Michigan University took issue with the latter assertion.