Homo habilis

The species in brief

Homo habilis sits right at the border between the older, more ape-like australopiths and the later humans who look more like us. Its brain was a little larger than an australopith’s, its teeth were smaller, and it lived at a time when stone tools were becoming part of everyday life. It is the species that first stretched the definition of Homo backward in time.

It is also one of the most argued-over species in human evolution. Scientists still disagree about which fossils belong to it, whether it was one species or two, and even whether it belongs in our genus.

How it was found and named

On 4 November 1960, Jonathan Leakey, the eldest son of Louis and Mary Leakey, found pieces of a young individual’s skull and jaw at Olduvai Gorge in Tanzania. The team nicknamed it “Jonny’s child”. Catalogued as OH 7 (Olduvai Hominid 7), it included a lower jaw with 13 teeth, two bones from the top of the skull, and 21 hand and wrist bones. It is about 1.8 million years old.

In 1964 Louis Leakey, the South African anatomist Phillip Tobias and the British primate expert John Napier named a new species from OH 7 and other Olduvai fossils: Homo habilis, the “handy man”. To fit it into Homo, they had to change the definition of the genus, including lowering the minimum brain size. Many experts were not convinced. The anatomist Wilfrid Le Gros Clark said he hoped habilis would “disappear as rapidly as he came”. It did not, but the argument never fully went away.

Body and brain

• Size. Small. Adults stood about 100 to 135 cm (3 ft 4 in to 4 ft 5 in) and averaged about 32 kg (70 lb).
• Brain. About 500 to 800 cubic centimetres, depending on which fossils are counted. That is a modest step up from Australopithecus.
• Face and teeth. A less projecting face than earlier hominins and smaller cheek teeth, though the enamel was still thick and the jaws strong.
• Arms and legs. The partial skeleton OH 62 showed surprisingly long arms compared with the legs, closer to an australopith’s proportions than to ours. Habilis walked upright but may still have climbed.
• Hands and feet. The hand bones from OH 7 suggest a grip able to hold and work stones. A fossil foot, OH 8, has an arch like a modern foot. OH 8 also carries bite marks that researchers have linked to a crocodile.

Food and tools

Wear on the teeth suggests a flexible diet: leaves, woody plants, fruit and some animal tissue. Habilis does not seem to have regularly chewed very hard foods like brittle nuts or hard tubers. That is a contrast with Paranthropus boisei, the heavy-jawed species that lived beside it.

Thousands of simple stone tools, known as Oldowan tools after Olduvai Gorge, were found in the same layers as the first habilis fossils. They are mostly sharp flakes knocked off river cobbles, good for cutting meat off bones and smashing bones for marrow. Animal bones with stone-tool cut marks show that meat and marrow were on the menu, though early humans may have scavenged carcasses as often as they hunted.

Was habilis the toolmaker?

When it was named, habilis got credit for the Olduvai tools. Since then the picture has become more complicated:

• The oldest Oldowan tools are about 2.6 million years old, slightly older than the oldest habilis fossils.
• At Nyayanga, on the shore of Lake Victoria in Kenya, Oldowan tools and butchered hippo bones about 2.6 to 3 million years old were found alongside two teeth of Paranthropus, not Homo. That does not prove Paranthropus made the tools, but it shows Homo was not the only possible toolmaker.
• Several kinds of hominin lived in the same places at the same time, so a tool found near a fossil does not say for certain who made it.

Most researchers still think habilis made and used stone tools. It just may not have been the first, or the only one.

Key fossils

• OH 7 (“Jonny’s child”). Olduvai Gorge, Tanzania, about 1.8 million years old. Found in 1960. The type specimen that the species is named from.
• OH 8. Olduvai Gorge. A nearly complete foot with a modern-style arch.
• OH 24. Olduvai Gorge. A crushed skull, the oldest skull from Olduvai and one of the most complete.
• OH 62. Olduvai Gorge, about 1.8 million years old. A partial skeleton found in 1986 by a team led by Donald Johanson and Tim White, pieced together from 302 fragments. It showed the species’ long arms.
• KNM-ER 1813. Koobi Fora, Kenya, about 1.9 million years old. One of the most complete skulls, with a brain of about 510 cc.
• KNM-ER 42703. Ileret, Kenya, about 1.44 million years old. An upper jaw found in 2000 and published in 2007. It is the youngest known habilis fossil.
• AL 666-1. Hadar, Ethiopia, about 2.3 million years old. An upper jaw found near where Lucy was discovered, one of the oldest fossils assigned to the species.

One species or two?

Skull KNM-ER 1470, found at Koobi Fora in 1972, has a bigger brain and a flatter, longer face than KNM-ER 1813, which is about the same age. Some researchers see the two as males and females, or simply variation, within one species. Many others put 1470 in a separate species, Homo rudolfensis. If they are right, at least two kinds of early Homo lived around Lake Turkana about 1.9 million years ago, alongside Paranthropus boisei and, a little later, Homo erectus.

Some scientists go further and argue that habilis is so close to the australopiths in body shape that it should be moved into Australopithecus. That remains a minority view.

Where it fits in the family tree

For a long time the story was simple: Australopithecus led to Homo habilis, which led to Homo erectus, which led to us. That ladder no longer holds.

In 2007 Fred Spoor, Meave Leakey and colleagues described two fossils from Ileret, east of Lake Turkana: the habilis jaw KNM-ER 42703, about 1.44 million years old, and a Homo erectus skull, KNM-ER 42700, about 1.55 million years old. Together they show the two species lived in the same lake basin for close to half a million years. That makes it unlikely that erectus evolved from habilis as we know it; they look more like related branches that both began earlier, perhaps between 2 and 3 million years ago.

The roots of Homo may go back further still. In 2015 researchers announced a lower jaw from Ledi-Geraru, Ethiopia, about 2.8 million years old, with a mix of Australopithecus and Homo features. It is classed as Homo, species undetermined, and is the oldest fossil yet put in our genus.

Sources

• Smithsonian National Museum of Natural History, Human Origins Program. Homo habilis.
• Leakey, L. S. B., Tobias, P. V. and Napier, J. R. (1964). A new species of the genus Homo from Olduvai Gorge. Nature 202: 7 to 9.
• Britannica. Homo habilis.
• Spoor, F., Leakey, M. G. and others (2007). Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya. Nature 448: 688 to 691.
• Villmoare, B. and others (2015). Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia. Science 347: 1352 to 1355.
• Plummer, T. W. and others (2023). Expanded geographic distribution and dietary strategies of the earliest Oldowan hominins and Paranthropus. Science 379: 561 to 566.
• Australian Museum. Homo habilis.