Nature 355, 719 - 722 (20 February 1992); doi:10.1038/355719a0

Earliest Homo

Andrew Hill^*, Steven Ward^†, Alan Deino^‡, Garniss Curtis^‡ & Robert Drake^‡

^*Department of Anthropology, Yale University, New Haven, Connecticut 06520, USA
^†Department of Human Anatomy, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272, USA
^‡Geochronology Centre of the Institute of Human Origins, 2453 Ridge Road, Berkeley, California 94709, USA

THE origin of our own genus, Homo, has been tentatively correlated with worldwide climatic cooling documented at about 2.4 Myr (million years) (refs 1–5). It has also been conjectured that members of Homo made the first stone tools, currently dated at 2.6–2.4 Myr (refs 6–8). But fossil specimens clearly attributable to Homo before about 1.9 Myr have been lacking. In 1967 a fossil hominoid temporal bone (KNM-BC1) from the Chemeron Formation of Kenya was described as family Hominidae gen. et sp. indet.⁹. Although a surface find, its provenance within site JM85 (BPRP site K002) was established and a stratigraphic section provided indicating the specimen's position⁹. This evidence has been affirmed (see for example refs 10–12) but the exact age of the fossil was never determined, and the absence of suitable comparative hominid material has precluded a more definitive taxonomic assignment. Here we present ⁴⁰Ar/³⁹Ar age determinations on material from the hominid site indicating an age of 2.4 Myr. In addition, comparative studies allow us to assign KNM-BC1 to the genus Homo, making it the earliest securely known fossil of our own genus found so far.

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