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In southwestern Kenya more than 2.6 million years ago, ancient humans wielded an array of stone tools—known collectively as the Oldowan toolkit—to pound plant material and carve up large prey such as hippopotamuses.

These durable and versatile tools were crafted from special stone materials collected up to eight miles away, according to new research led by scientists at the Smithsonian's National Museum of Natural History, Cleveland Museum of Natural History and Queens College.

Their findings, in the journal Science Advances, push back the earliest known evidence of ancient humans transporting resources over long distances by some 600,000 years.

"People often focus on the tools themselves, but the real innovation of the Oldowan may actually be the transport of resources from one place to another," said Rick Potts, the senior author of the study and the National Museum of Natural History's Peter Buck Chair of Human Origins.

"The knowledge and intent to bring stone material to rich food sources was apparently an integral part of toolmaking behavior at the outset of the Oldowan."

In the new study led by Emma Finestone, the Robert J. and Linnet E. Fritz Endowed Chair of Human Origins at the Cleveland Museum of Natural History, Finestone and Potts worked with several colleagues to analyze stone tools uncovered on Kenya's Homa Peninsula, a fossil-rich region that juts out into the eastern margins of Lake Victoria.

Potts first surveyed the region's fossil sites in 1985. In the years since, he has worked closely with colleagues at the National Museums of Kenya to excavate the area's gullies as part of the ongoing Homa Peninsula Paleoanthropology Project, which Potts co-directs with Queens College professor Thomas Plummer, another co-author of the new paper.

Finestone joined the project in 2012, when she began working with Plummer to reconstruct hominin tool behavior on the Homa Peninsula and understand how toolmakers moved around the landscape.

One of the peninsula's most significant sites is known as Nyayanga and contains archaeological finds dating back some three million years. A series of recent excavations yielded a trove of stone tools and hundreds of butchered hippopotamus bones.

In a 2023 paper, Plummer, Potts, Finestone and their colleagues posited that these bones represent the oldest known evidence of ancient hominins using stone tools to butcher large animals.

"Hominins were using stone tools for a variety of pounding and cutting tasks, including processing plant and animal foods and working wood," Plummer said. "The diversity of activities that used stone tools suggests that, even at this early stage of cultural development, stone tools enhanced the adaptability of the hominins using them."

The development of the made it possible for early humans to consume large prey. Around three million years ago, ancient hominins began refining their toolmaking, using hammerstones to strike stone cores and create sharp-edged flakes. By pounding, slicing and scraping, these stone tools could process and refine a greater variety of plant and animal materials.

Finding the right rocks was vital. Oldowan tools needed to be fashioned from stones that were strong yet brittle enough to easily flake.

However, the local rocks at Nyayanga are relatively soft, and would produce cutting tools that would quickly dull and pounding tools that would be more likely to shatter. Like using a flimsy plastic knife trying to cut through a well-done steak, these stones would have been of little use for pounding tough plants or breaking animal bones.

As a result, hominins at Nyayanga appear to have brought in stronger stones from other areas. The researchers analyzed the geochemistry of hundreds of stone cores and flakes found at Nyayanga that date back at least 2.6 million years. They discovered that these tools were crafted from volcanic rocks like rhyolite and metamorphic rocks like quartzite.

The scientists surveyed local geology and discovered that these rock types were common in drainage basins several miles east of the Homa Peninsula.

According to Finestone, Nyayanga stones are significantly older than other known examples of ancient stone transport. Previously, the oldest evidence of hominins moving rocks over significant distances was a 2-million-year-old site known as Kanjera South that is also located on the Homa Peninsula.

"It's surprising because the Nyayanga assemblage is early in the Oldowan and we previously thought that longer transport distances may have been related to changes that happened in our more recent evolutionary history," she said.

The distance ancient hominins traveled for stones analyzed in this study is also noteworthy. While many nonhuman primates carry food and rocks, they only utilize materials that are nearby. Some, like chimpanzees, are known to transport stones over short distances. But the hominins at Nyayanga appear to have consistently procured material from over six miles away.

The ability to transport resources is a major milestone in human evolution. According to Potts, it exhibits ancient hominins' ability to plan ahead and assess the requirements for processing food. It also illustrates an ability to mentally map their environment and remember locations with high-quality rocks.

"The mental maps of the oldest known hominins to persistently make stone tools well surpassed their immediate surroundings, even surpassing a few miles," Potts said.

Once ancient hominins brought their lithic haul back to Nyayanga, they fashioned the stones into flakes and cores. But the identity of these toolmakers remains elusive.

At the oldest hippo butchery site, the team discovered a molar tooth from a hominin in the genus Paranthropus, a group that sported strong skulls and teeth to grind tough material. Another Paranthropus tooth was found nearby on the surface of the same geological bed.

The existence of Paranthropus teeth alongside Oldowan stone tools hints that these hominins may have used stone tools like their in the genus Homo.

However, the case is far from closed.

"Unless you find a hominin fossil actually holding a tool, you won't be able to say definitively which species are making which stone tool assemblages," Finestone said. "But I think that the research at Nyayanga suggests that there is a greater diversity of hominins making early stone tools than previously thought."

The artifacts at Nyayanga also underscore that ancient humans have transported raw materials to fuel technological innovations for millions of years.

"Humans have always relied on tools to solve adaptive challenges," Finestone said. "By understanding how this relationship began, we can better see our connection to it today—especially as we face new challenges in a world shaped by technology."