A reassessment of a fossil tooth from an old archaeological collection suggests that early hominins had extended their range to the western branch of Africa’s Great Rift Valley by no later than two million years ago. Since the late 1950s, large numbers of early hominin fossils have been found in the eastern branch of the Great Rift Valley, which is often described as the Cradle of Humanity. However, up until now, none have been found in the western branch.
Ishango 11 is an archaeological site in the Democratic Republic of Congo; it is located alongside the Semliki River, in the western branch of the Great Rift Valley. In the 1950s, the site was excavated by the Belgian geologist Jean de Heinzelin, who recovered numerous fossil human and animal remains, together with stone and bone artefacts. The assemblage dates mainly to the early part of the African Late Stone Age, from 25,000 to 19,000 years ago. It is housed in the Department of Anthropology and Prehistory at the Royal Belgian Institute of Science, Brussels.
However, the finds also included an upper left first molar that did not appear to be from such a recent period. Known as #Ish25, doubts were cast on its affinities to modern humans as long ago as 1958. A recent study has shown that #Ish25 probably originated from an earlier geological layer than the other fossils and artefacts. Animal remains associated with this layer suggest that it dates to between 2.6 and 2.0 million years ago. These dates make #Ish25 the earliest fossil hominin find from the western branch of the Great Rift Valley (though not the earliest from Central Africa, as much earlier hominins are known from Chad).
Various statistical analyses of the shape and size of #Ish25 suggest closer affinities to hominins from the Late Pliocene/Early Pleistocene than those from the Middle Pleistocene to Recent epochs. The exact hominin species to which the tooth belongs cannot be determined with certainty; Australopithecus africanus, Paranthropus robustus and early Homo are all possibilities.
The western Great Rift Valley underwent episodes of climate change 3.0, 2.6 and 1.8 million years ago; these led to the partial replacement of Congo flora and fauna with those typical of the East Africa; the latter are adapted to more open grassland conditions. The #Ish25 findings suggest that these conditions led to a dispersal of hominins into the region from either East Africa or South Africa.
The study also demonstrates how valuable knowledge can often be gained by applying modern techniques to old anthropological collections.
1. Crevecoeur, I. et al., First Early Hominin from Central Africa (Ishango, Democratic Republic of Congo). PLoS One 9 (1), e84652 (2014).