Homo habilis - A large-brained precursor of modern humans

Homo habilis (click to enlarge) Photo: Luna04

Location of Olduvai Gorge Map: Sémhur

Location of Tanzania Map: Vardion

In 1960, Louis Leakey's son Jonathan found the first material to be assigned to Homo habilis. The find was made at Olduvai Gorge in northwestern Tanzania (then Tanganyika). This individual, now known as specimen OH 7 ("Olduvai hominid 7"), was 1.75 million years old. The remains included a lower mandible, with 13 teeth, two parietal bones, and twenty-one small bones from the hands (Lieberman et al. 1996).

Homo habilis (click to enlarge) Credit: Rafaela Monteiro

The parietals — the left nearly complete — were used to estimate a cranial capacity of about 363 cc. The remains were those of a 12- or 13-year-old male, which suggested an adult brain size of about 700 cc. So OH 7 is beyond the high end of the range of australopithecine variation, yet far smaller than Homo erectus. Homo habilis' brain was about half as large as that of a modern human.

Another more complete specimen, a 1.89-million-year-old skull, was found in 1972 by Bernard Ngeneo, of Richard Leakey's "Hominid Gang," near Lake Turkana in Kenya. Known as skull 1470, it had a cranial capacity of 750 cc.

Homo habilis is the oldest hominid assigned to the genus Homo, and the least similar to modern humans (Homo sapiens) of any of the forms in that genus, except perhaps Homo rudolfensis. But its facial structure and small teeth — both rather similar to those of modern humans — its large cranial capacity, and the precision of its grip (suggested by the hand bones), have convinced most paleoanthropologists that habilis is appropriately placed in the genus Homo. Indeed, many initially believed Homo habilis skulls looked too modern to be of such great age. Primitive stone tools often accompany H. habilis remains, but there is no clear evidence of the use of fire.

Homo habilis was short in comparison to modern humans — males stood no more than 1.3 m (4 ft 3 in) tall — and had apishly long arms. H. rudolfensis was more apelike than H. habilis, and so has been proposed as the immediate ancestor of the latter. This is certainly questionable since H. habilis remains are known from a much earlier date — 2.5 million years ago — than are those of H. rudolfensis, which date to 1.9 million years before present (although one fossil, KNM-ER 1470, attributed to H. rudolfensis may, or may not date to as early as 2.5 mya).

It has also often been suggested that H. habilis was the ancestor of Homo erectus. But recent findings (Spoor et al. 2007) indicate the two coexisted for some 500,000 years (read BBC article). The most recent H. habilis remains known date to 1.44 million years ago, while the earliest material assigned to H. erectus dates to about two million years ago. So it seems most unlikely that H. habilis evolved into H. erectus. As is usually the case with distinct types of hominids, the exact nature of their relationship remains unresolved.