Our Stone Tool Discovery Pushes Back the Archaeological Record by 700,000 Years

Jason Lewis, Stony Brook University and Sonia Harmand, Stony Brook University

On the morning of July 9 2011, we were climbing a remote hill near the western shore of Lake Turkana in northern Kenya.

Sammy Lokorodi, who made the initial discovery.

Our field team had accidentally followed the wrong dry riverbed, the only way of navigating these remote desert badlands, and we were scanning the landscape for a way back to the main channel. Something felt special about this particular place, so before moving on, we all fanned out and surveyed the patch of craggy outcrops. By teatime, local Turkana team member Sammy Lokorodi had helped us spot what we had come searching for.

We, and the West Turkana Archaeological Project which we co-lead, had discovered the earliest stone artifacts yet found, dating to 3.3 million years ago. The discovery of the site, named Lomekwi 3, instantly pushed back the beginning of the archaeological record by 700,000 years. That’s over a quarter of humanity’s previously known material cultural history. These tools were made as much as a million years before the earliest known fossils attributed to our own genus, Homo.

Harmand unearthing a stone tool at the site.

Stretching the record further back

Stone tools are fossilized human behavior. – Louis Leakey

In the 1930s, famed paleoanthropologists Louis and Mary Leakey unearthed early stone artifacts at Olduvai Gorge in Tanzania. They named them the Oldowan tool culture. Later, in the 1960s, they found hominin fossils in association with those Oldowan tools that looked more like later humans than the Australopithecines discovered there previously. The Leakeys assigned them to a new species: Homo habilis, or handy man.

Since then, conventional wisdom in human evolutionary studies has supposed that the origins of knapping stone tools by our ancestors – that is, chipping away flakes from a stone to make a tool – were linked to the emergence of the genus Homo. The premise was that our lineage alone took the cognitive leap of hitting stones together to strike off sharp flakes, and that this was the foundation of our evolutionary success. Scientists thought this technological development was tied to climate change and the spread of savanna grasslands; our ancestors innovated with new tools to help them survive in an evolving landscape.

Over the last few decades, however, subsequent discoveries pushed back the date for the earliest stone tools to 2.6 million years ago (Ma) and the earliest fossils attributable to early Homo to only 2.4-2.3 Ma. By necessity, there’s been increasing openness to the possibility of tool manufacture before 2.6 Ma and by hominins other than Homo.

A series of papers published in rapid succession in early 2015 have solidified these ideas into an emerging paradigm shift in paleoanthropology: the fossil record of the genus Homo now extends back to 2.8 Ma in the Ethiopian Afar; cranial and post-cranial diversity in early Homo is much wider that previously thought, already evincing several distinct lineages by 2 Ma; and Australopithecus africanus and other Pleistocene hominins, traditionally considered not to have made stone tools, have a human-like trabecular bone pattern in their hand bones that’s consistent with tool use.