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
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. By this time, the Leakeys had spent 29 years excavating in Olduvai Gorge for early hominin remains, but had instead recovered mainly other animal remains as well as the Oldowan stone-tool industry. The industry had been ascribed to Paranthropus boisei (at the time "Zinjanthropus") in 1959 as it was the first and only hominin recovered in the area, but this was revised upon OH 7's discovery. In 1964, Louis, South African palaeoanthropologist Phillip V. Tobias, and British primatologist John R. Napier officially assigned the remains into the genus Homo, and, on recommendation by Australian anthropologist Raymond Dart, the specific name H. habilis, meaning "able, handy, mentally skillful, vigorous" in Latin. The specimen's association with the Oldowan (then considered evidence of advanced cognitive ability) was also used as justification for classifying it into Homo. 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.
Many had accepted Tobias' model and assigned Late Pliocene to Early Pleistocene hominin remains outside the range of Paranthropus and H. erectus into H. habilis. For non-skull elements, this was done on the basis of size as there was a lack of clear diagnostic characteristics. Because of these practices, the range of variation for the species became quite wide, and the terms H. habilis sensu stricto (i.e. strictly) and H. habilis sensu lato (i.e. broadly) were in use to exclude and include, respectively, more discrepant morphs. To address this controversy, English palaeoanthropologist Bernard Wood proposed in 1985, that the comparatively massive skull KNM-ER 1470 from Lake Turkana, Kenya, discovered in 1972 and assigned to H. habilis, actually represented a different species, now referred to as Homo rudolfensis. It is also argued that instead it represents a male specimen whereas other H. habilis specimens are female. Early Homo from South Africa have variously been assigned to H. habilis or H. ergaster / H. erectus, but species designation has largely been unclear. In 2010, Australian archaeologist Darren Curoe proposed splitting off South African early Homo into a new species, "Homo gautengensis".
In 1986, OH 62, a fragmentary skeleton was discovered by American anthropologist Tim D. White in association with H. habilis skull fragments, definitively establishing aspects of H. habilis skeletal anatomy for the first time, and revealing more Australopithecus-like than Homo-like features. Because of this, as well as similarities in dental adaptations, Wood and biological anthropologist Mark Collard suggested moving the species to Australopithecus in 1999. However, reevaluation of OH 62 to a more humanlike physiology, if correct, would cast doubt on this. The discovery of the 1.8 Ma Georgian Dmanisi skulls in the early 2000s, which exhibit several similarities with early Homo, has led to suggestions that all contemporary groups of early Homo in Africa, including H. habilis and H. rudolfensis, are the same species and should be assigned to H. erectus.
Classification
There is still no wide consensus as to whether or not H. habilis is ancestral to H. ergaster / H. erectus or is an offshoot of the human line, and whether or not all specimens assigned to H. habilis are correctly assigned or the species is an assemblage of different Australopithecus and Homo species. Studies of the dental morphology of H. habilis have suggested that it shares greater similarity with Australopithecus than with later Homo species. Nonetheless, H. habilis and H. rudolfensis generally are recognised members of the genus at the base of the family tree, with arguments for synonymisation or removal from the genus not widely adopted.
Though it is now largely agreed upon that Homo evolved from Australopithecus, the timing and placement of this split has been much debated, with many Australopithecus species having been proposed as the ancestor. The discovery of LD 350-1, the oldest Homo specimen, dating to 2.8 mya, in the Afar Region of Ethiopia may indicate that the genus evolved from A. afarensis around this time. This specimen was initially classified as Homo sp., though subsequent studies have suggested that it also shares characteristics with Australopithecus and that it is clearly distinct from H. habilis. The oldest H. habilis specimen, A.L. 666-1, dates to 2.3 mya, but is anatomically more derived (has less ancestral, or basal, traits) than the younger OH 7, suggesting derived and basal morphs lived concurrently, and that the H. habilis lineage began before 2.3 mya. Based on 2.1-million-year-old stone tools from Shangchen, China, H. habilis or an ancestral species may have dispersed across Asia. The youngest H. habilis specimen, OH 13, dates to about 1.65 mya.
Anatomy Skull
It has generally been thought that brain size increased along the human line especially rapidly at the transition between species, with H. habilis brain size smaller than that of H. ergaster / H. erectus, jumping from about in H. habilis to about in H. ergaster and H. erectus. However, a 2015 study showed that the brain sizes of H. habilis, H. rudolfensis, and H. ergaster generally ranged between after reappraising the brain volume of OH 7 from to . This does, nonetheless, indicate a jump from australopithecine brain size which generally ranged from .
The brain anatomy of all Homo features an expanded cerebrum in comparison to australopithecines. The pattern of striations on the teeth of OH 65 slant right, which may have been accidentally self-inflicted when the individual was pulling a piece of meat with its teeth and the left hand while trying to cut it with a stone tool using the right hand. If correct, this could indicate right handedness, and handedness is associated with major reorganisation of the brain and the lateralisation of brain function between the left and right hemispheres. This scenario has also been hypothesised for some Neanderthal specimens. Lateralisation could be implicated in tool use. In modern humans, lateralisation is weakly associated with language.
The tooth rows of H. habilis were V-shaped as opposed to U-shaped in later Homo, and the mouth jutted outwards (was prognathic), though the face was flat from the nose up.
Build Based on the fragmentary skeletons OH 62 (presumed female) and KNM-ER 3735 (presumed male), H. habilis body anatomy has generally been considered to have been more apelike than even that of the earlier A. afarensis; this is consistent with an at least partially arboreal lifestyle in the trees as is assumed in australopithecines. Based on OH 62 and assuming comparable body dimensions to australopithecines, H. habilis has generally been interpreted as having been small-bodied like australopithecines, with OH 62 generally estimated at in height and in weight. However, assuming longer, modern humanlike legs, OH 62 would have been about and , and KNM-ER 3735 about the same size. For comparison, modern human men and women in the year 1900 averaged and , respectively. It is generally assumed that pre-H. ergaster hominins, including H. habilis, exhibited notable sexual dimorphism with males markedly bigger than females. However, relative female body mass is unknown in this species.