Homo habilis

The earliest of our ancestors to show a significant increase in brain size and also the first to be found associated with stone tools.

Age

This species lived between about 2.3 and 1.5 million years ago.

What the name means

Homo, is a Latin word meaning ‘human’ or ‘man’. This is the same genus or group name as the one give to modern humans and is used to show the close relationship between this species and our own.

The word habilis is based on a Latin word meaning ‘handy’ or ‘skilful’. This species known as ‘handy man’ because stone tools were found near its fossil remains and it is assumed this species had developed the ability to modify stone into tools.

The discovery of Homo habilis began in 1959 when two teeth were unearthed at Olduvai Gorge in Tanzania by a team led by Louis and Mary Leakey. Parts of a boy’s skeleton were located at the site the next year and additional fossils from other individuals continued to be found.

Their brain size, features of their hands and feet, and evidence that they may have used stone tools all suggested that a new type of human ancestor had been found. They were officially announced as new species in 1964 but their placement into the human genus Homo was controversial. Additional fossils, including the discovery of a partial skeleton in 1986, have revealed that this species was more ape-like than previously believed.

Important specimens

• OH 62 - a 1.8-million-year-old partial skeleton disovered in1986 by Tim White in Olduvai Gorge, Tanzania. These remains are thought to be those of a female because of the short stature. This partial skeleton was discovered as 302 fragments of fossilised tooth and bone. It was an important discovery because it enabled this species’ arm, leg and body proportions to be determined. These proportions revealed that this Homo habilis was more ape-like than previously believed. Like apes, this individual had relatively long arms and short legs.
• KNM-ER 1813 – a 1.9-million-year-old skull discovered in1973 by Kamoya Kimeu in Koobi Fora, East Turkana, Kenya. This adult skull has a brain size of only 510 cubic centimetres, which is only just above the average for species placed in the Australopithecus genus.
• ‘Twiggy’ OH 24 – a 1.8-million-year-old skull discovered in 1968 by Peter Nzube in Olduvai Gorge, Tanzania. When found, this skull had been badly crushed and was reconstructed from hundreds of fragments. It also shows some distortion of the bones that occurred before fossilisation was complete.
• ‘Cindy’ OH 13 – a 1.7-million-year-old lower jaw discovered in Olduvai Gorge, Tanzania. This jaw was found with other pieces of the skull and a lower arm bone.
• ‘Jonny’s Child’ OH 7 – a 1.8-million-year-old partial skeleton discovered in 1960 by Jonathan Leakey in Olduvai Gorge, Tanzania. This partial skeleton belongs to a boy and was selected as the ‘type specimen’ or official representative of this species.
• OH 35 – lower leg bones discovered in 1960 in Olduvai Gorge, Tanzania. These leg bones and the OH 8 foot bones may have come from the same individual.
• OH 8 – 1.8-million-year-old foot bones discovered in 1960 in Olduvai Gorge, Tanzania. This partial left foot lacks its heel and toe bones but the foot’s arch and general shape are similar to our own and provide evidence that this species’ walking gait was identical to that of a modern human.
• AL 666-1 – a lower jaw Homo sp. (species unknown) discovered in 1994 in Hadar, Ethiopia. This jaw has the distinctive dental arch of humans. It has therefore been classified in the genus Homo, but its actual species designation is uncertain – it may be Homo habilis or it may even be a totally new species of early human. At 2.3 million years in age it is the oldest known Homo found directly associated with stone tools.
• KNM-ER 42703 – a right upper jaw bone dated to about 1.44 million years old, discovered in Ileret Kenya in 2000. It is the youngest fossil of Homo habilis yet found.

Distribution

Fossils of this species have been found in the countries of Kenya and Tanzania in Africa, in particular at Lake Turkana, Olduvai Gorge and Koobi Fora.

Relationships with other species

This species was initially considered to be a direct ancestor of modern humans but fossil discoveries in the mid-1980s showed that Homo habilis had rather ape-like limb proportions. This evidence led to a reassessment of Homo habilis and its relationship to modern humans. Many scientists no-longer regard this species as one of our direct ancestors and instead have moved it onto a side branch of our family tree.

The debate about Homo habilis continues following the discovery of some skulls at Dmanisi in the Republic of Georgia. Two of the skulls are very similar to Homo ergaster but one appears to have features intermediate between Homo habilis and Homo ergaster and may represent a link between these two species. If so, Homo habilis may be a direct ancestor of modern humans or that they both evolved from a yet-undiscovered species. Homo habilis arose at a time when there is a relative gap in the fossil record (between 2 and 3 million years ago). This makes it difficult to determine where it came from or how it is related to the earlier australopithecines. More fossil evidence is needed to resolve this issue.

Other names

Homo habilis has been a controversial species ever since the name was first announced. The fossils originally named Homo habilis have now been split into two groups. One group retains the name Homo habilis although some scientists prefer the name Australopithecus habilis because these individuals have physical similarities with the australopithecines.

The other group consists of fossils with larger brains and larger teeth, including the skull KNM-ER 1470 and jaw KNM-ER 1802. These individuals are now placed in a different species but there is debate as to whether these fossils should be named Homo rudolfensis, Australopithecus rudolfensis or Kenyanthropus rudolfensis.

The Homo habilis and Homo rudolfensis debate

Scientists often disagree about naming fossil specimens. Scientific names may be changed following new discoveries, different interpretations or new lines of investigation. Homo habilis is a well-known but poorly defined species and scientific opinions about the attributed specimens vary widely. Two specimens at the centre of the debate are KNM-ER 1470 and KNM-ER 1813.

KNM-ER 1470 (discovered 1972)

• about 1.7 million years old
• large brain, about 750-800ml
• teeth not preserved; roots and sockets suggest they were large, as in Australopithecus, with larger molars than other Homo habilis specimens
• square upper jaw
• slightly developed brow ridge
• face large and flat and longer than KNM-ER 1813

KNM-ER 1813 (discovered 1973)

• about 1.7 million years old
• small brain, about 500ml
• small upper jaw with human-like teeth
• rounded upper jaw
• strongly developed brow ridge
• face small and not very flat

The differences between KNM-ER 1470 and KNM-ER 1813 can be interpreted in various ways.

• Different Sexes - other things being equal, large bodied individuals have a bigger head and brain than small individuals. KNM-ER 1813 may be a female and KNM-ER 1470 may be a male of Homo habilis. However, they do not differ from each other in the sort of ways that males and females of modern apes (including humans) differ from one another.
• Different Species - scientists claim that 1813 and 1470 represent two species, or even two genera. Suggestions include Australopithecus africanus, Homo habilis and Homo rudolfensis. The discovery of a skull of Kenyanthropus platyops in 1999, and its similarity to KNM-ER 1470, has led some to consider reclassifying KNM-ER 1470 into the Kenyanthropus genus.

Homo habilis had a larger brain than earlier human ancestors and this is reflected in significant changes to the shape of the skull. However, many other features including limb proportions are similar to those of the earlier australopithecine ancestors.

Body size and shape

• body proportions were similar to those of australopithecines with females growing to about 110 centimetres and males to about 130 centimetres in height.

Brain

• brain averaged 610 cubic centimetres in size, representing 1.7 per cent of their body weight. This was a significant increase compared to australopithecine brains.

Skull

• brain case had become fuller and more rounded due to expansion of the brain
• beginnings of a slight forehead were appearing
• face had a small, arched brow ridge and was smaller and shorter than those of earlier ancestors
• hole for the spinal cord was located in the centre of the skull base, showing that this species walked on two legs
• facial projection was reduced compared with earlier species

Jaws and teeth

• jaw was smaller than those found in the earlier australopithecines
• teeth were arranged in a more rounded arc like those of modern humans
• teeth had become smaller and more human-like, although the incisors were still relatively large

Limbs

• features of the leg and foot bones indicate that this species walked on two legs.
• legs were relatively short, providing this species with arm and leg proportions that were relatively ape-like and similar to those of the australopithecines.
• finger bones are slightly curved and intermediate in shape between the curved finger bones of quadrupedal apes and the straight finger bones of modern humans
• finger bone proportions suggest the human-like ability to form a precision grip

How they lived

Homo habilis may have been the first of our ancestors to make stone tools. This represented a significant change in mental capabilities and a shift toward new survival strategies.

The first crude stone tools consisting of simple choppers, core tools and scrapers were made as early as 2.6 million years ago and are classified as Mode 1 technology. It is uncertain who the makers of these earliest stone tools were. The tool makers may have been early populations of Homo habilis or they may have been made by another species. One such candidate is represented by the fossil AL 666-1, which has been provisionally named Homo sp. (meaning a human whose species is currently unknown).

Mode 1 technology includes core tools, choppers and smaller flakes used as scrapers. They are often called Oldowan stone tools as the first discoveries of these tools occurred at Oldoway (now Olduvai) Gorge, Tanzania in east Africa. These tools were a simple progression from the use of sticks and natural, unmodified stones that our earliest ancestors probably used. The chopping or cutting edges on Oldowan tools were created by using one stone (the hammerstone) to strike another (the core) in order to remove one or more rock fragments (flakes).

Environment and diet

Homo habilis lived in a predominantly grassland environment. The climate was becoming cooler and drier and this may have been the impetus for new feeding strategies that included scavenging and tool use. Chemical analysis suggests that this species was mainly vegetarian but did include some meat in their diet.