Homo habilis is an extinct hominin that lived in Africa between 2.3 and 1.6 million years ago. The type specimen, OH 7 (Olduvai Hominid #7), was discovered by Louis Leakey at Olduvai Gorge, Tanzania, in 1960. It consists of a mandible and two parietal (skull) bones that are 1.7 million years old. The species (literally, “handy man”) got its name from the association of the fossil with stone tools.
Homo habilis is distinguished from Australopithecus primarily on the basis of a larger brain, smaller molars, and aspects of the hand that support an anatomical basis for toolmaking. The brain of Homo habilis is estimated to have been between 500 and 710 cc (depending on the specimen). On average, it is larger than that of australopithecines but smaller than that of Homo erectus. The body size of Homo habilis has been estimated to be about 32 kg (70.5 lbs). Relative to its body size, Homo habilis had a large brain.
There is a great deal of variation among specimens attributed to Homo habilis. Some specimens show limb proportions that are similar to australopithecines (longer arms relative to legs), while others do not. It is clear, however, that Homo habilis was a biped. A nearly complete foot from Olduvai Gorge clearly shows characters associated with bipedal locomotion. These include the presence of both middle and longitudinal arches, the alignment of the second through fifth toes, and the enlarged big toe that is in line with, rather than opposable to, the other toes. There is some indication from the foot, however, that Homo habilis also spent some time in the trees. Muscle markings on the bone suggest that the foot could be easily inverted (turned sideways), which would facilitate tree climbing.
Homo habilis was once associated with the earliest evidence for making stone tools, and paleoanthropologists considered them to be the first toolmakers. These tools consist of choppers and flakes and belong to the Oldowan tradition. The tools made by Homo habilis were most likely used for scavenging meat, not hunting prey. Interestingly, there is good evidence that Homo habilis was a major staple in the diet of large cats and other predatory animals. Therefore, rather than being “man the hunter,” Homo habilis was more likely “man the hunted.”
Recently, Oldowan tools that predate Homo habilis have been found in Ethiopia. These date to 2.5 to 2.6 million years ago. The younger tools are associated with Australopithecus remains (A. garhi). The older tools are not associated with any fossils. Based on this new evidence, it now seems possible that Australopithecus, rather than Homo, was the first hominin to make and use stone tools.
To date, indisputable Homo habilis fossils have not been found outside Africa. This suggests that the migration of early humans to Europe and Asia came later in human evolution. In fact, most human cultural evolution occurred in later Homo species. There is no clear evidence that Homo habilis controlled fire or buried their dead. Neither is there unequivocal evidence that Homo habilis was capable of vocalizing sounds recognizable as language today.
Since the original discovery of the OH 7 specimen, many more specimens attributed to Homo habilis have been discovered. Their remains vary quite a bit in size and shape. Based on this variation, there is debate among paleoanthropologists about whether or not the fossils attributed to Homo habilis represent a single species. Those who believe there is more than one species separate the fossils into Homo habilis and Homo rudolfensis.
The Homo rudolfensis specimens are distinguished from the Homo habilis specimens by having larger postcanine teeth with more complex premolar roots, larger brains, and more humanlike limb proportions (shorter arms/longer legs). The species Homo rudolfensis was proposed in 1986 by V. P. Alexeev for the specimen KNM ER 1470, which was originally assigned to the genus Homo but had not been assigned to a species. Since then, several other fossils once attributed to Homo habilis or Homo erectus have been reassigned (by some) to Homo rudolfensis. For those who accept dividing Homo habilis into two species, there is little agreement about where in human evolutionary history Homo rudolfensis lies.
When Homo habilis was discovered, it was thought to be the ancestor to all later Homo. It was more humanlike than the australopithecines that had been found and less specialized than the known Homo erectus fossils from Asia. However, as more fossils have been discovered, the position of Homo habilis in the human lineage has become less clear. In the conservative interpretation (one species), it may have been the ancestor to both Homo erectus and Homo ergaster. In a less conservative interpretation (two species), Homo habilis may have given rise to Homo rudolfensis (which, in turn, gave rise to Homo erectus/ergaster), or it may have been an evolutionary side branch.
Toolmaking was once considered to be one of the defining characteristics of humanity. It was its association with stone tools that led paleoanthropologists to hypothesize that Homo habilis was more similar to modern humans than it was to australopithecines. We now know, however, that there is a diversity of toolmaking and tool-using behavior among chimpanzees. This has forced paleoanthropologists to revise their assumptions about what makes us human. Tool use can no longer be used as the criterion for a genus.
Wood and Collard claim that in order for a specimen to be classified as Homo, it should meet a number of criteria. These include showing greater similarity to Homo sapiens than to australopithecines in body size, body proportions, and in the size and shape of teeth and jaws. To be included in the genus Homo, a specimen should also show evidence of modern humanlike bipedal locomotion (with limited climbing capability) and of a modern humanlike extended period of growth and development. These researchers argue that Homo habilis (including H. rudolfensis) does not meet these criteria. As a result, they have suggested that it be removed from the genus Homo and reassigned to the genus Australopithecus (for example, A. habilis).
References:
- Asfaw, B., White, T., Lovejoy, O., Latimer, B., Simpson, S., & Suwa, G. (1999). Australopithecus garhi: A new species of early hominid from Ethiopia. Science, 284, 629-635.
- Delagnes, A., Brugal, J.-P., Feibel, C., Kibunjia, M., Mourre, V., & Texier, P.-J. (1999). Early hominid stone tool production and technical skill 2.34 Myr ago in West Turkana, Kenya. Nature, 399, 57-60.
- Wood, B., & Collard, M. (1999). The human genus. Science’s Compass, 284, 65-71.
