Homo habilis ( 'handy man') is an extinct species of archaic human from the Early Pleistocene of East and South Africa about 2.4 million years ago to 1.65 million years ago (mya). It is among the oldest species of archaic humans. Suggestions for pushing back the age to 2.8 Mya were made in 2015 based on the discovery of a jawbone. Upon species description in 1964, H. habilis was highly contested, with many researchers recommending it be synonymised with Australopithecus africanus, the only other early hominin known at the time, but H. habilis received more recognition as time went on and more relevant discoveries were made. By the 1980s, H. habilis was proposed to have been a human ancestor, directly evolving into Homo erectus, which directly led to modern humans. This viewpoint is now debated. Several specimens with insecure species identification were assigned to H. habilis, leading to arguments for splitting, namely into "H. rudolfensis" and "H. gautengensis" of which only the former has received wide support.
H. habilis brain size generally varied from . The body proportions of H. habilis are only known from two highly fragmentary skeletons, and is based largely on assuming a similar anatomy to the earlier australopithecines. Because of this, it has also been proposed H. habilis be moved to the genus Australopithecus as Australopithecus habilis. However, the interpretation of H. habilis as a small-statured human with inefficient long-distance travel capabilities has been challenged. The presumed female specimen OH 62 is traditionally interpreted as having been in height and in weight assuming australopithecine-like proportions, but assuming humanlike proportions she would have been about and . Nonetheless, Homo habilis may have been at least partially arboreal like what is postulated for australopithecines. Early hominins are typically reconstructed as having thick hair and marked sexual dimorphism with males much larger than females, though relative male and female size is not definitively known.
H. habilis manufactured the Oldowan stone tool industry and mainly used tools in butchering. Early Homo, compared to australopithecines, are generally thought to have consumed high quantities of meat and, in the case of H. habilis, scavenged meat. Typically, early hominins are interpreted as having lived in polygynous societies, though this is highly speculative. Assuming H. habilis society was similar to that of modern savanna chimpanzees and baboons, groups may have numbered 70–85 members. This configuration would be advantageous with multiple males to defend against open savanna predators, such as big cats, hyenas and crocodiles. H. habilis coexisted with H. rudolfensis, H. ergaster / H. erectus and Paranthropus boisei.
Taxonomy
Research history
thumb|left|[[KNM-ER 1813 reconstructed skull and jaw]]
The first recognised remains—OH 7, partial juvenile skull, hand, and foot bones dating to 1.75 million years ago (mya)—were discovered in Olduvai Gorge, Tanzania, in 1960 by Jonathan Leakey, with other native Africans who dug into Olduvai Gorge, and who worked for Jonathan Leakey. However, the actual first remains—OH 4, a molar—were discovered by the senior assistant of Louis and Mary Leakey (Jonathan's parents), Heselon Mukiri, other native Africans, in 1959, but this was not realised at the time. OH 7 was designated the holotype specimen.
After description, it was hotly debated if H. habilis should be reclassified into Australopithecus africanus (the only other early hominin known at the time), in part because the remains were so old and at the time Homo was presumed to have evolved in Asia (with the australopithecines having no living descendants). Also, the brain size was smaller than what Wilfrid Le Gros Clark proposed in 1955 when considering Homo. The classification H. habilis began to receive wider acceptance as more fossil elements and species were unearthed. In 1983, Tobias proposed that A. africanus was a direct ancestor of Paranthropus and Homo (the two were sister taxa), and that A. africanus evolved into H. habilis which evolved into H. erectus which evolved into modern humans (by a process of cladogenesis). He further said that there was a major evolutionary leap between A. africanus and H. habilis, and thereupon human evolution progressed gradually because H. habilis brain size had nearly doubled compared to australopithecine predecessors.