Cradle of humanity is still revealing new insights about our origins

This is an extract from Our Human Story, our newsletter about the revolution in archaeology. Sign up to receive it in your inbox every month.

Near the eastern shore of Lake Turkana in Kenya, there is a hill called Namorotukunan. A river once flowed past it, but it has long since dried up. The undulating landscape is dry, dotted with scrubby vegetation.

Between 2013 and 2022, researchers led by David Braun at George Washington University in Washington DC excavated the layers of clay left behind by the river. There they found 1290 stone tools made by ancient humans between 2.44 and 2.75 million years ago. They reported their finds in Nature Communications last week.

The tools were of a type known as Oldowan, which have been found in many sites across Africa and Eurasia. They are some of the earliest and simplest stone tools. Furthermore, the ones from Namorotukunan are some of the oldest Oldowan tools yet found.

The thing that leapt out to Braun and his colleagues was the consistency of the objects. Despite these items spanning 300,000 years, the hominins that were making them created pretty much the same kinds of tools, and they were systematically choosing the best rocks for their purposes. This suggests these early uses of tools were not short-lived one-offs, invented and then quickly forgotten. Instead, tool-making was something early hominins did habitually.

The Namorotukunan tools are just the latest discovery to come out of one of the most important places on Earth for understanding our origins: the Omo-Turkana basin.

Basin, cradle and rift

Beginning in the 1960s, the Omo-Turkana basin has been at the heart of studies of human evolution.

It begins in the white sands of southern Ethiopia, where the Omo River flows south into Lake Turkana. One of the largest lakes in the world, Lake Turkana is long and thin, extending far to the south into Kenya. Two other rivers, the Turkwel and Kerio, drain into its southern reaches.

There are fossil-bearing regions dotted all over the basin. On the lake’s west side is the Nachukui Formation, while to the east lies Koobi Fora. There are also sites along the rivers, including the Usno Formation near the Omo in the north, and Kanapoi near the Kerio in the south.

Researchers led by François Marchal at Aix-Marseille University in France have drawn together all the known hominin fossils from the Omo-Turkana basin. They’re developing a database to showcase them all, and in the meantime they have described the overall patterns in the Journal of Human Evolution. The compilation is both a time capsule of research into palaeoanthropology and a goldmine of information about human evolution.

Research in the Omo-Turkana basin began with “early expeditions to the Omo Group deposits by a joint French, American, and Kenyan team led by Camille Arambourg, Yves Coppens, F. Clark Howell, and Richard Leakey”. Leakey also led a team that explored Koobi Fora in the east, and then western areas like Nachukui.

Richard Leakey might ring a bell – he was a big figure in human evolution research in the 1960s, 70s and 80s. He was the son of Louis and Mary Leakey, who did pioneering research in Oldupai (formerly Olduvai) gorge in Tanzania – and his daughter Louise is still a palaeoanthropologist today.

However, the study of the Omo-Turkana basin is much bigger than one man or even one family. From the sites in the region, Marchal and his colleagues totted up 1231 hominin specimens from an estimated 658 individuals, which they say is about one-third of all the hominin remains known from Africa.

Along with the Great Rift valley in East Africa (which includes Oldupai gorge and many other sites) and the Cradle of Humankind in South Africa, the Omo-Turkana basin is one of the three most productive hominin fossil localities in Africa.

The discoveries

In the north, near the Omo River, researchers found some of the oldest remains of our species (Homo sapiens) on the planet. At Omo Kibish, researchers found two partial skulls and various other bones, plus hundreds of teeth. The more we study these remains, the older they seem to be. Originally claimed to be 130,000 years old, a 2005 study pushed them back to 195,000 years ago – and a 2022 follow-up indicated they were at least 233,000 years old. Of all the remains of Homo sapiens, only the Jebel Irhoud fossils from Morocco, which are around 300,000 years old, are more ancient.

The Omo Kibish and Jebel Irhoud fossils are some of the key evidence our species is significantly older than we once thought. Instead of evolving around 200,000 years ago, we may have been evolving independently for several hundred thousand years.

Something similar appears to be true of the Homo genus, which includes us as well as other groups like Homo erectus and the Neanderthals. Precisely when Homo first evolved is tricky to nail down. There are definitely Homo by 2 million years ago, but as we go further back in time the record becomes murkier.

By drawing together all the fossils from the Omo-Turkana basin, Marchal and his colleagues found Homo is well-represented in the region from 2.7 to 2 million years ago.

The oldest-known Homo specimens from the basin are from the Shungura Formation and are 2.74 million to 2.58 million years old. However, despite having been announced in 2008, they have still not been described in detail.

Despite such frustrating gaps, Marchal’s team found “no fewer than 45 individuals of early Homo arising from 2.7 to 2.0”. If they were to add in the undescribed material, they suggest, “there are likely to be 75 individuals of early Homo, making this a substantial and significant assemblage” – or, as they say, “more than a smattering of fossils”.

The implication is the Homo genus was pretty well-established in the Omo-Turkana basin between 2.7 and 2 million years ago. They weren’t dominant – another genus called Paranthropus, which had smaller brains and bigger teeth, was twice as common. There were also a lot of Australopithecus, though their time was drawing to a close. The basin was a place where many hominin species lived side by side. But Homo were there, and they may have made some of those Oldowan tools.

Findings like these are only possible through this sort of sustained study over decades. I expect the Omo-Turkana basin will keep telling us more about our origins for many years.