Pruning the family tree

, but raises new questions.

Feb 21, 2003
Doug Broadfield(broadfie@fau.edu)

A spate of new species added to an already crowded human family has caused our once elegant evolutionary tree to look more like a gangly bush. But, in February 21 Science, Robert Blumenschine and colleagues at the Department of Anthropology, Rutgers University, New Jersey, US, describe a new find from Olduvai Gorge in Tanzania that could simplify the number of species present at the origin of our genus, Homo (Science, 299:1217-1221, February 21, 2003).

Almost 40 years ago Louis Leakey and his colleagues described a series of fossils from Olduvai Gorge as the oldest member of our genus. Because of its large brain size, almost 700ml, and associated stone tools, the find was dubbed Homo habilis, literally "handy man". Nearly a decade later Leakey's son Richard discovered a more complete skull in northern Kenya, expanding the reach of Homo habilis across much of the Rift Valley of eastern Africa. This single species model at the root of Homo remained unchanged until the mid-1980's when the members of H. habilis were split into two groups, with all of the fossils found at Olduvai Gorge keeping the original designation, H. habilis, and the others — displaying a flattened sub-nasal area and, in some specimens, more robust dentition — taking the new name, Homo rudolfensis.

Blumenschine et al. suggest that at least some of the members of these two early groups of Homo should be reunited into a single species. The new find, designated OH 65 and dated to 1.8 million years ago, consists of a portion of the lower face and upper jaw with all its teeth. Based on comparisons with another fossil from northern Kenya, they propose that the Kenyan fossil currently designated as H. rudolfensis, KNM-ER-1470, and OH 65 should be placed with related fossils from Olduvai Gorge into a single species, H. habilis. This is possible, because the new fossil and 1470 share several features, including the flat face below the nose and dental structure, which once led to the species' separation.

In lumping these fossils together Blumenschine et al. have forced out other fossils once belonging to H. habilis, and created the need for another, as yet unnamed, species of early Homo. Thus, while they have helped to create a clearer picture of H. habilis eking out a life along the wooded shorelines of the ancient lakes Olduvai and Turkana 1.8 million years ago, they have done little to simplify the overall portrait of early Homo. For this we will have to wait for other, more complete finds to determine which early Homo gave rise to us.