We’ve only just confirmed that Homo habilis really existed

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Homo habilis is a paradoxical species. On the one hand, they have a famous name and hold the status of being the first members of our genus Homo: the first humans, if you like. On the other hand, we have never known that much about them, and what we do know is kind of weird. How can a species be simultaneously well known and little known?

We have to start with the name, if only because it’s one of the few things we can be sure about. The species was given its moniker in 1964 by a trio of palaeoanthropologists: Louis Leakey, Phillip Tobias and John Napier. Though, as they acknowledged, it wasn’t their idea – their colleague Raymond Dart had suggested “habilis” from the Latin for “able, handy, mentally skilful, vigorous”.

They applied the name to a collection of bones and teeth they had found in Olduvai/Oldupai gorge in Tanzania, East Africa. The remains were rather miscellaneous: a lower jaw with teeth, an upper molar, skull bones called parietals and some hand bones. The trio interpreted them as belonging to a single juvenile individual.

Crucially, the researchers asserted that Homo habilis were the makers of Oldowan stone tools, which had been found in the locality. By saying this, they made the broader claim that making tools was a defining feature of the genus Homo. Less “human-like” hominins such as Australopithecus probably didn’t make tools, but Homo habilis and their ever-brainier descendants did, and that was what marked them as special.

That is a lot of interpretation to put on a handful of fossils, but let’s be forgiving. Very few hominin fossils were known at the time and Leakey and his colleagues were doing their best with what they had.

Over the following 62 years, researchers found more fossils that they assigned to H. habilis. However, the additional remains haven’t clarified our understanding of the species. On the contrary, H. habilis has languished.

“It’s what they call a wastebasket taxon,” says Ian Tattersall at the American Museum of Natural History in New York. “Whenever [researchers] found something that they weren’t quite sure what it was, they just chucked it into Homo habilis. And so pretty soon, Homo habilis became a rather unwieldy assemblage of stuff that you would find it very difficult to define.”

So, can we make sense of this crucial species and its place in our origins?

A new find

This has all become relevant again because a new H. habilis specimen has come to light. It was excavated in 2012 and 2014 from the Koobi Fora Formation at Ileret, Kenya. Researchers led by Frederick Grine at Stony Brook University in New York and Ashley Hammond at the Catalan Institute of Palaeontology Miquel Crusafont in Barcelona described the remains in The Anatomical Record on 13 January. Grine and Hammond were unable to talk to me, but Tattersall published a commentary on the find on 24 January and we talked on the phone (both of us struggling with the worst connection ever).

The new specimen is the most complete H. habilis ever found. It includes a collarbone (clavicle), fragments of the shoulder blade (scapula), both upper arm bones (humerus), both of each of the two lower arm bones (ulna and radius) and fragments of the base of the spine (sacrum) and hip bone (os coxae).

There’s still a lot missing: the head, ribcage, spine, hands, legs and feet. But it’s enough to figure out a lot about H. habilis.

The most obvious thing is that H. habilis had relatively long arms. One of the big trends in human evolution is for arms to become shorter: our ape cousins have long arms, relative to their legs, whereas our arms are decidedly shorter. Compared with other Homo species like Homo erectus, H. habilis had long arms.

For Tattersall, this is evidence that H. habilis was still spending a fair bit of time in trees, where long arms are an advantage. Before Homo, earlier hominins like Australopithecus seem to have lived hybrid lifestyles where they spent some time in trees and some time walking on two legs on the ground. “It’s a way of life that has no equivalent in the contemporary world, but obviously it was a very successful one for a long time,” he says. Whereas later Homo species like H. erectus were pretty committed to bipedal walking on the ground, H. habilis still had one foot in the trees.

The skeleton also suggests that H. habilis was fairly slight. The researchers estimated that the individual stood about 160 centimetres tall yet weighed just 30 to 33 kilograms. That’s smaller than most H. erectus specimens, again marking H. habilis as distinct.

There are still lots of things we don’t know. We have very little information about the diet of H. habilis or their social dynamics and group size. It’s also unclear how long the species was around for or how widespread they were.

Still, it does seem like H. habilis’s days of being a wastebasket taxon might be over.

An identity

In his commentary, Tattersall lists the fossils that have been assigned to H. habilis over the past six decades. They include a fragmentary skeleton and cranium from East Turkana in Kenya, a fragmentary skeleton and palate from Olduvai, another palate from Hadar in Ethiopia, a partial lower jawbone from Ledi-Geraru in Ethiopia and a single cranium from Sterkfontein in South Africa.

Tattersall calls these fossils a “motley assortment”, and he’s not wrong. There are few H. habilis bones that we have more than one copy of, so we can’t be confident that the ones we have are representative.

This has led to decades of uncertainty. Some of the purported H. habilis fossils might not belong to the species, or even the Homo genus. In particular, the South African one is widely thought to be an Australopithecus, suggesting H. habilis only lived in East Africa.

Some researchers have even argued that the entire species is a sort of mirage: a bunch of bits and pieces of late Australopithecus and early Homo, lumped together for no good reason.

The new specimen suggests we can rule out this most extreme possibility and accept most of the purported specimens. Incomplete as it is, “it seems to have the basic characteristics of most of the other skeletons that have been called Homo habilis”, says Tattersall. Those isolated bits and pieces do, on the whole, match the more complete skeleton.

That’s not to say this clears it all up. Tattersall says everything above the neck is still a bit of a mystery: “The skulls and the teeth make up a rather odd assemblage when you put them all together.” Since the new skeleton doesn’t include anything from the head, it doesn’t help us sort out which ones belong together.

The timeline and range of H. habilis also need clearing up. “Homo habilis is something that we now know, thanks to the new specimen, was around, at least in Tanzania and Kenya, between about 1.8 and 2 million years ago,” says Tattersall.

It’s possible the species was around earlier or later, but that’s less clear. The oldest claimed specimen is a partial lower jawbone from Ledi-Geraru in Ethiopia, dated to 2.8 million years ago. “In my view, it’s not Homo habilis,” says Tattersall. Even though it seems to be more closely related to Homo than to Australopithecus, that doesn’t mean it’s necessarily H. habilis, he says. Tattersall suggests that the group that gave rise to Homo was emerging around that time.

This means it’s an open question whether H. habilis was really the first member of the Homo genus. It used to look like Homo erectus (African specimens of which are sometimes called Homo ergaster) only emerged later. However, recent fossil finds have pushed the species back in time: we now have specimens of H. erectus from at least 1.85 million years ago and even 2 million years ago. Combine that with the uncertainties around the H. habilis fossil record and it’s not obvious which species is older.

Ultimately, what all this means is that the origin of our genus is still something of a mystery. We have fossils that are telling us something about it, but we can’t be quite sure what they’re saying. The “simple” narrative is that a group of Australopithecus evolved into H. habilis and some of those later evolved into H. erectus (aka H. ergaster). But maybe there were a lot of Homo species living in parallel, right from the off. Or maybe something else happened.

If that seems a bit unsatisfying, just remember: we now know that Homo habilis was probably real. Last year, that wasn’t obvious.

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