RUTGERS (US)—Human footprints found in Kenya suggest that some of the earliest humans walked like us and did so on anatomically modern feet.

The footprints were found in two 1.5 million-year-old sedimentary layers near Ileret in northern Kenya.  The Ileret footprints constitute the oldest evidence of an essentially modern human-like foot anatomy, according to analysis by John W.K. Harris, professor of anthropology at Rutgers University, and lead study author Matthew Bennett of Bournemouth University in the United Kingdom. These rarest of impressions have revealed information about soft tissue form and structure not normally accessible in fossilized bones.

Harris directs Rutgers’ Koobi Fora Field Project in Kenya. From 2006 to 2008, the field school group of mostly American undergraduates, including Rutgers students, excavated the site that yielded the footprints.

The upper sediment layer contained three footprint trails: two trails of two prints each, one of seven prints, and a number of isolated prints. Five meters deeper, the other sediment surface preserved one trail of two prints and a single isolated smaller print, probably from a juvenile.

In these specimens, the big toe is parallel to the other toes, unlike that of apes where it is separated in a grasping configuration useful in the trees. The footprints show a pronounced human-like arch and short toes, typically associated with an upright bipedal stance. The size, spacing, and depth of the impressions were the basis of estimates of weight, stride, and gait, all found to be within the range of modern humans.

Based on size of the footprints and their modern anatomical characteristics, the researchers attribute the prints to the hominid Homo ergaster, or early Homo erectus as it is more generally known. This was the first hominid to have had the same body proportions (longer legs and shorter arms) as modern Homo sapiens. Various H. ergaster or H. erectus remains have been found in Tanzania, Ethiopia, Kenya, and South Africa, at dates consistent with the Ileret footprints.

Other hominid fossil footprints dating to 3.6 million years ago had been discovered in 1978 by Mary Leakey at Laetoli, Tanzania. These are attributed to the less advanced Australopithecus afarensis, a possible ancestral hominid. The smaller, older Laetoli prints show indications of upright bipedal posture but possess a shallower arch and a more ape-like, divergent big toe.

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