Homo habilis

Introduction:
Homo habilis ("handy man") is an early human species that lived between 2.33 to 1.44 million years ago and is quite possibly the earliest member of genus Homo, though acceptance of it being an ancestor to modern humans or indeed of it being a human species at all is not universal. The species was first described by Louis Leakey in 1964.

Fossil Record:
Homo habilis is known from fossils recovered from Olduvai Gorge, Tanzania; East Turkana, Kenya; Sterkfontein, South Africa; and Hadar in the Awash Valley of Afar Depression, Ethiopia.

The first specimen to be discovered, now known as OH7, comprising a partial cranium and mandible, was discovered by Jonathon and Mary Leakey at Olduvai Gorge on 4 November 1960 and has been dated to 1.75 million years old. Other findings from Olduvai Gorge include OH 24, a cranium discovered by Peter Nzube in 1968 and believed to be 1.8 million years old; OH 13 (partial cranium, mandible and maxilla, discovered by N. Mbuika in 1963, 1.66 million years old); OH 8 (foot, probably from the same individual as OH 7, discovered 1960) and OH 62 (partial skeleton, including upper and lower limbs, believed to be female, discovered by Donald Johanson and Tim White in 1986, 2.0 million years old).

KNM-ER 1805 and KNM-ER 1813 were both discovered at Koobi Fora, East Turkana. KNM-ER 1805 is a partial cranium, maxilla, and mandible, dated to 1.74 million years old. The finder and the date of discovery are unknown. KNM-ER 1813 is a cranium dated to 1.8 million years old discovered by K. Kimeu in 1973.

KNM-ER 42703, also from Koobi Fora, is a right maxilla with an estimated geological age of 1.44 million years. It was discovered by John E. Kaatho in 2000. This is the youngest specimen assigned to Homo erectus, and is notable for being younger than KNM-ER 42700: a small, well preserved calvaria with an estimated geological age of 1.55 million years that has been assigned to (African) Homo erectus.

The Sterkfontein specimens include the partial cranium STW-53 discovered by A.R. Hughes in 1976 and dated 1.5 – 2.0 million years old.

From Hadar comes the maxilla AL-666-1, discovered by William Kimball and dated to 2.33 million years old, the oldest specimen with affinities to Homo habilis.

Description:
Homo habilis had a cranial capacity of between 509-675cc (Cameron & Groves, 2004), considerably larger than its putative ancestors, the australopithecines (375-500cc); and that of present-day chimpanzees (400cc), but much less than that of modern humans. It had a prognathic face (jutting jaw), moderate brow-ridges; no saggital keeling (a raised area along the centre of the skullcap); reduced dentition relative to australopithecines; and proportionately long arms and short legs relative to modern humans. It had an ape-like conical ribcage and possibly retained the ape-like ability of arboreal locomotion.

There was a degree of sexual dimorphism in the species. OH 62 which, as noted above, is believed to have been female, was about 1m tall and probably weighed 30kg. Males were probably around 1.3m tall and weighed around 36kg.

Technology:
Homo habilis is generally associated with the Oldowan industry (or Mode I), named for Olduvai Gorge by Louis and Mary Leakey because they were first recognised there. The Oldowan is the earliest stone tool industry and examples dating to around 2.5 million years old are known from Gona, Bouri and Hadar in Ethiopia; from Lokalelei, West Turkana, Kenya dating to 2.4 million years old; from Koobi Fora dating to 1.9 million years old and from Olduvai Gorge dating to 1.8 million years old.

The Oldowan is associated with a number of hominin species and is therefore a toll-making tradition rather than a particular culture. In addition to Homo habilis, the tradition may be associated with Parantropus (“robust australopithecines”) and the “late” gracile species Australopithecus garhi. The latter, discovered in 1997, was found in association with large animal bones showing cut-marks from stone tools. Although no actual tools were directly associated with the fossils, it seems likely that A. garhi made and used stone tools. The remains have been dated to 2.5 million years old. In addition, the Oldowan survived Homo habilis and is associated with a number of later human species.

The Oldowan is characterised by very simple stone tools. The main types are choppers made from cobbles or angular blocks of stone; hammer-stones, which are unmodified chunks that show signs of having been used as hammers in tool manufacture; scrapers made from both cores and retouched flakes detached from cores. Although there is a considerable variety and other types such as discoids and polyhedrons are recognised, much of the variation can be explained in terms of differences in the nature of the raw material available. The overall strategy was likely a least-effort strategy to produce either flakes with sharp cutting edges or cores for chopping. It seems unlikely that the Oldowan toolmakers mastered the sophisticated stone reduction strategies seen in later tool-making traditions.

Evolutionary history of Homo habilis:
The accepted view of human evolution has become considerably more complicated over the last twenty years and it is now recognised that the traditional view of progressive evolution from australopithecine to H. habilis to H. erectus and finally to H. sapiens is at best an oversimplification.

The picture for Homo habilis was complicated in the 1980s by the discovery that fossils previously assigned to Homo habilis actually belonged to two species – Homo habilis and Homo rudolfensis, although it does now seem likely that the latter is an australopithecine-type upright ape, off the line of human evolution.

Homo habilis is believed to have evolved from an australopithecine species, but there is no consensus as to which of those currently known, if any. The traditional assumption that Homo ergaster (i.e. African Homo erectus) evolved from Homo habilis has recently been challenged by the discovery that the two species were sympatric (co-existing) in the Lake Turkana basin in Kenya for almost half a million years, implying that they must have occupied different niches and leading some to believe that the two species diverged from a common ancestor 2.3 million years ago rather than one evolving from the other.

On the other hand Homo habilis appears in the fossil record some 300,000 years before Homo ergaster. Unless earlier H. ergaster remains come to light, it seems likely that a proto-ergaster population split away from an earlier population of H. habilis and only later came into contact with a population of the ancestral species.

For now, then, it is still widely accepted that Homo habilis is ancestral to all later human species, including Homo sapiens.

References:

Cameron D & Groves C (2004): Bones, Stones and Molecules: “Out of Africa” and Human Origins, Elsevier Academic Press.

Leakey LSB, Tobias PV & Napier JR (1964): A New Species of Genus Homo from Olduvai Gorge, Nature No. 4927, 4 April 1964.

Scarre C (2005) (Ed): “The human past”, Thames & Hudson.

F. Spoor, M. G. Leakey, P. N. Gathogo, F. H. Brown, S. C. Anton, I. McDougall, C. Kiarie, F. K. Manthi & L. N. Leakey (2007): Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya, Nature Vol 448 9 August 2007.

© Christopher Seddon 2009