Fossils and artefacts unearthed in Kenya suggest our ancestors used stone stools to feed on large animals in the distant past.
The stone tools found in Kenya are up to three million years old.Credit: T. W.
Plummer, J. S. Oliver and E. M. Finestone, Homa Peninsula Paleoanthropology Project
Some of the oldest stone tools ever found have offered a rare glimpse into the lives of early humans and their relatives.
An archaeological excavation on the shore of Lake Victoria in Kenya has unearthed hundreds of stone tools and fossils dating to as early as three million years ago. These tools — found alongside teeth from human relatives and the butchered remains of ancient hippopotamus-like creatures — provide some of the first direct evidence that early hominins used stone tools to feed on large animals. A study describing them was published on 9 February in Science1.
The site now joins a handful of others that have yielded tools dating back to the earliest adoption of stone technology. “This is a dream site,” says Sonia Harmand, an archaeologist at Stony Brook University in New York. “It’s so remarkable, it’s almost too good to be true.”
Gaps in the archaeological record have made it challenging to study toolmaking in our earliest ancestors. Hominins — the group of primates that includes Homo sapiens and its relatives — first started using tools at least 3.3 million years ago. Researchers know this because of stone tools unearthed at a single site in northern Kenya.
But the next known set of stone tools — called Oldowan tools — doesn’t pop up in the archaeological record for another 700,000 years. This type of tool eventually became widespread across Africa and into Asia. But the dearth of artefacts from between the two early sites means that finding out how tools were made and used during this period of almost one million years is a challenge.
The site in Kenya is now offering some fresh insights. In the early 2000s, a worker at an excavation near Lake Victoria told researchers that he’d seen stone tools and animal fossils popping out of the ground near his home.
The crew started excavating at the new site in 2015. Over several field seasons, they unearthed 330 artefacts, including 42 Oldowan stone tools scattered around the bones of an ancestral hippo. Some of the hippo bones, as well as other animal remains at the site, bore signs of being cut and scraped by stone implements.
A fossilized hippo skeleton was found alongside the tools.Credit: T. W. Plummer, Homa Peninsula Paleoanthropology Project
Dating methods placed the remains between 2.6 million and 3 million years old, making the associated artefacts a contender for the oldest cache of Oldowan tools ever found. It also pushes back the known start of large-animal butchering by hominins by at least 600,000 years. Microanalysis of some of the tools suggested some were used to pound plant material, possibly hard roots or tubers.
These findings suggest that stone tools were crucial for accessing hard-to-get foods, says co-author Thomas Plummer, a palaeoanthropologist at Queens College, City University of New York in Flushing. Early hominins would have been limited by what they could tear with their hands and teeth, he says. Stone tools “allowed them to work food outside of their mouths”.
“A hippopotamus is like a giant leather sack,” he adds. “It’s full of stuff you could eat, but without stone tools, you can’t get at it.”
Who killed the hippos?
Stone tools and fossilized animal bones weren’t the only remains to come out of the site. As a thunderstorm rolled in on the last day of the field season in 2017, the researchers also stumbled on a tooth that belonged to an ancient relative of humans from a genus called Paranthropus. Its presence near the hippo carcasses — along with another Paranthropus tooth also found at the site — raises the possibility that it might have been members of Paranthropus, rather than of the modern-human genus Homo, that used some of the stone tools at the site to butcher the animals.
It isn’t that surprising that other hominin lineages might have made tools, considering that the first known tools pre-date the emergence of Homo, says Harmand. But others are more sceptical. “I personally do not believe that Paranthropus made Oldowan tools,” says Mohamed Sahnouni, a palaeolithic archaeologist at the National Research Centre on Human Evolution in Burgos, Spain. He says that the hominin’s anatomy suggests that it was well adapted to eating coarse foods and might not have needed to master tool use.
However, Sahnouni adds that the finds are still “a major breakthrough” that “sheds light on the behaviour of early Oldowan toolmakers”.