World's Oldest Stone Tools Unearthed in Kenya

Acheulian hand axes. Our ancestor Homo erectus used shaped stone tools like these to butcher animal carcasses. Photo courtesy: Pierre-Jean Texier/CNRS

A rare haul of picks, flakes and hand axes recovered from ancient sediments in Kenya are the oldest remains of advanced stone tools yet discovered.

Archaeologists unearthed the implements while excavating mudstone banks on the shores of Lake Turkana in the remote north-west of the country.

The largest of the tools are around 20cm long and have been chipped into shape on two sides, a hallmark of more sophisticated stone toolmaking techniques probably developed by Homo erectus, an ancestor of modern humans.

Trenches dug at the same site revealed remains of long-gone species that shared the land with those who left the tools behind. Among them were primitive versions of hippopotamuses, rhinos, horses, antelopes, and dangerous predators such as big cats and hyenas.

The stone tools, made for crushing, cutting and scraping, gave early humans a means to butcher animal carcasses, strip them of meat and crack open their bones to expose the nutritious marrow.

Researchers dated the sediments where the tools were found to 1.76m years old. Until now, the earliest stone tools of this kind were estimated to be 1.4m years old and came from a haul in Konso, Ethiopia. Others found in India are dated more vaguely, between 1m and 1.5m years old.

Older, cruder stone tools have been found. The most ancient evidence of toolmaking by early humans and their relatives dates to 2.6m years ago and includes simple pebble-choppers for hacking and crushing. These Oldowan tools, named after the Olduvai gorge in Tanzania, were wielded by our predecessors for around a million years.

But the latest collection of stone tools from Kenya belong to a second, more advanced generation of toolmaking. Known as Acheulian tools after a prominent archaeological site in France, they are larger, heavier and have sharp cutting edges that are chipped from opposite sides into the familiar teardrop shape.

Most Acheulian stone tools have been recovered from sites alongside fossilised bones of Homo erectus, leading many archaeologists to believe our ancestors developed the technology as an improvement on the Oldowan toolmaking skills they inherited.

"The Acheulian tools represent a great technological leap," said Dennis Kent, a geologist involved in the study at Rutgers University in New Jersey and Columbia University's Lamont-Doherty Earth Observatory in New York.

Writing in the journal Nature, a team of researchers led by Kent's colleague Christopher Lepre describe finding the stone tools in a region called Kokiselei in the Rift Valley. The site is close to where several spectacular human fossils have been found, including Turkana Boy, an early human teenager who lived 1.5m years ago.

Unearthing the tools has raised fresh questions about the skills possessed by different groups of H. erectus as they spread across the globe. Lepre's team found both Oldowan and Acheulian stone tools at Kokiselei, but no evidence for advanced stone tools has been found at a site occupied by H. erectus 1.8m years ago in Dmanisi in Georgia. This, Kent said, presents a problem if H. erectus originated in Africa and migrated to Asia, as many archaeologists believe. "Why didn't Homo erectus take these tools with them to Asia?"

One radical explanation offered by researchers is that H. erectus originated in Asia instead of Africa. Another possibility is that groups migrating from Africa into Asia lost the skills to make Acheulian tools along the way.

Chris Stringer, head of human origins at the Natural History Museum in London and author of a new book, The Origin of Our Species, said the latest haul of Acheulian tools were "very crude by the standards of later examples".

"In terms of the Out of Africa event, new dating of the Dmanisi site in Georgia places some of the material from there older than 1.8m years ago, so it is evident that human emergence from Africa preceded even this new date for bifacial tools. In fact some researchers believe the first exodus from Africa could have been even earlier than the date for Dmanisi, by a pre-erectus population making Oldowan tools," he said.

"In the deep past, with small populations that were prone to local or wider extinctions, innovations did not always take hold and spread. Novelties like blade tools and bows and arrows may have been invented and reinvented many times over, due to the loss of individuals and populations, and the knowledge they carried.

"So we cannot be sure that the tools found at Kokiselei were really the beginning of the establishment of the Acheulian. Populations could have experimented with bifacial working many times before it took hold more widely around 1.6m years ago."