The oldest known widespread stone-tool technology, called the Oldowan, is thought to have arisen in East Africa some 2.6 million years ago and then spread across the continent.
But new evidence suggests that the technology, rough all-purpose tools chipped out of pebbles, might actually have popped up independently in different parts of Africa. This is according to archaeologists who have discovered stone tools and butchered animal bones on a high Algerian plateau.
The newly discovered limestone and flint tools are about 2.4 million years old — almost the same age as the oldest known such tools, which were found in Gona, Ethiopia, and are 2.6 million years old.
The discovery means that hominins were present in the Mediterranean fringe of North Africa around 600,000 years earlier than previously thought. The work is published on 29 November in Science1.
As with the earliest stone-tool finds in East Africa, researchers didn't discover any hominin remains nearby, so it's not clear whether the items were made by a species of Homo or a related genus.
The discovery raises the possibility that hominins awoke to the idea of tool use in several parts of Africa at once, rather than simply adopting a fashion that spread from the East African Rift Valley, according to the research team, led by archaeologist Mohamed Sahnouni of the Spanish National Research Center for Human Evolution in Burgos.
Sahnouni’s team spent eight years probing the Ain Boucherit site in northern Algeria. They've unearthed a trove of chopping and cutting tools alongside the notched and hammered bones of elephants, hyenas, pigs, crocodiles and other animals.
In the Rift Valley, objects yield their age relatively easily, thanks to argon–argon dating of the volcanic ash deposits in which they are found. There are no such rocks in the Algerian mountains.
So the scientists used three separate techniques to constrain the date: magnetostratigraphy, which exploits a rock’s record of the direction of Earth’s magnetic field at the moment it solidified; electron spin resonance of quartz grains in the deposits, to deduce the date at which an object was buried; and checking the periods during which the animals whose bones were found with the tools were known to have existed.
None of these is a direct technique, but since the three approaches concur, the team is confident that their results are correct.
The age difference between these tools and those found in the Rift Valley is too short for the stone technology to have journeyed across the deserts and mountains to North Africa, says Sahnouni. “I think this argues soundly for a multiple origin of stone technology.”
Much of the early hominin-fossil and stone-tool record comes from East Africa — largely because of the research tradition kicked off there by the spectacular fossil and tool findings of anthropologists Louis Leakey and Mary Leakey in the 1950s and 1960s, says Sahnouni. But also because of the ease of preservation and dating, which creates a possible bias in the data.
“We should beware of building elaborate origins scenarios based on where we have the best preservation,” says Chris Stringer, a human-evolution specialist at the Natural History Museum in London. “It also remains to be determined whether there were direct connections between North and East African hominins about 2.4 million years ago, or whether [they] could have been evolving largely independently.”
Ignacio de la Torre, an archaeologist at University College London, agrees that there has probably been an overemphasis on the importance of East Africa in this field. But he also points to the 2015 report from a Kenyan site of stone tools dating back to some 3.3 million years ago2. If the Kenyan discovery is confirmed, he adds, “that will show that stone technology emerged in East Africa first”.
Sahnouni, M. et al. Science https://doi.org/10.1126/science.aau0008 (2018).
Harmand, S. et al. Nature 521, 310–315 (2015).