An international team of scientists has unearthed a collection of 2.6-million-year-old systematically flaked stone tools at the site of Bokol Dora 1 (BD1) in the Ledi-Geraru area, Ethiopia. Previously, the oldest evidence for systematic stone tool production and use was 2.58 million to 2.55 million years ago. The team’s work, published in the Proceedings of the National Academy of Sciences, suggests that stone tools may have been invented many times in many ways before becoming an essential part of the human lineage.

The Bokol Dora 1 (BD 1) site was first discovered in 2012 by researchers with the Ledi-Geraru Research Project.

“At first we found several artifacts lying on the surface, but we didn’t know what sediments they were coming from,” said Dr. Chris Campisano, a geologist at Arizona State University.

“But when I peered over the edge of a small cliff, I saw rocks sticking out from the mudstone face. I scaled up from the bottom using my rock hammer and found two nice stone tools starting to weather out.”

“It took several years to excavate through meters of sediments by hand before exposing an archaeological layer of animal bones and hundreds of small pieces of chipped stone representing the earliest evidence of our direct ancestors making and using stone knives.”

The recent discovery of older hammering or ‘percussive’ stone tools in Kenya dated to 3.3 million years ago, described as Lomekwian, and butchered bones in Ethiopia shows the deep history of our ancestors making and using tools.

However, discoveries of tools made by chimpanzees and monkeys have challenged ‘technological ape’ ideas of human origins.

Dr. Campisano and colleagues wondered how the discovery of the BD 1 tools fit into this increasingly complex picture.

What they found was that not only were these new tools the oldest artifacts yet ascribed to the Oldowan, a technology originally named after finds from Olduvai Gorge in Tanzania, but also were distinct from tools made by chimpanzees, monkeys or even earlier human ancestors.

“We expected to see some indication of an evolution from the Lomekwian to these earliest Oldowan tools. Yet when we looked closely at the patterns, there was very little connection to what is known from older archaeological sites or to the tools modern primates are making,” said coauthor Will Archer, of the Max Planck Institute for Evolutionary Anthropology in Leipzig and the University of Cape Town.

The major differences appear to be the ability for our ancestors to systematically chip off smaller sharp-edged tools from larger nodules of stone.

Chimpanzees and monkeys generally use tools for percussive activities, to hammer and bash food items like nuts and shellfish, which seems to have been the case with the 3.3 million-year-old Lomekwian tools as well.

Something changed by 2.6 million years ago, and our ancestors became more accurate and skilled at striking the edge of stones to make tools. The BD 1 artifacts captures this shift.

It appears that this shift in tool making occurred around the same time that our ancestor’s teeth began to change. This can be seen in LD 350-1, a 2.8-million-year-old partial jaw of early Homo from Ledi-Geraru.

As our ancestors began to process food prior to eating using stone tools, we start to see a reduction in the size of their teeth. Our technology and biology were intimately intertwined even as early as 2.6 million years ago.

The lack of clear connections with earlier stone tool technology suggests that tool use was invented multiple times in the past.

“Given that primate species throughout the world routinely use stone hammers to forage for new resources, it seems very possible that throughout Africa many different human ancestors found new ways of using stone artifacts to extract resources from their environment,” said Dr. David Braun, an archaeologist with George Washington University.

“If our hypothesis is correct, then we would expect to find some type of continuity in artifact form after 2.6 million years ago, but not prior to this time period. We need to find more sites.”

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David R. Braun et al. Earliest known Oldowan artifacts at >2.58 Ma from Ledi-Geraru, Ethiopia, highlight early technological diversity. PNAS, published online June 3, 2019; doi: 10.1073/pnas.1820177116