Acheulean tools on the left, Middle Stone Age tools on the rightHuman Origins Program / Smithsonian

When Rick Potts started digging at Olorgesailie, the now-dry basin of an ancient Kenyan lake, he figured that it would take three years to find everything there was to find. That was in 1985, and Potts is now leading his fourth decade of excavation. It’s a good thing he stayed. In recent years, his team has uncovered a series of unexpected finds, which suggest that human behavior and culture became incredibly sophisticated well before anyone suspected—almost at the very dawn of our species, Homo sapiens.

The team found obsidian tools that came from sources dozens of miles away—a sign of long-distance trade networks. They found lumps of black and red rock that had been processed to create pigments—a sign of symbolic thought and representation. They found carefully crafted stone tools that are indicative of the period known as the Middle Stone Age; that period was thought to have started around 280,000 years ago, but the Olorgesailie tools are between 305,000 and 320,000 years old.

Collectively, these finds speak to one of the most important questions in human evolution: When did anatomically modern people, with big brains and bipedal stances, become behaviorally modern, with symbolic art, advanced tools, and a culture that built on itself? Scientists used to believe that the latter milestone arrived well after the former, when our species migrated into Europe between 50,000 and 60,000 years ago, and went through a “creative explosion” that produced the evocative cave art of Lascaux and Chauvet. But this conspicuously Eurocentric idea has been overturned by a wealth of evidence showing a much earlier origin for modern human behavior—in Africa, the continent of our birth.

The new discoveries at Olorgesailie push things back even further. They suggest that many of our most important qualities—long-term planning, long-distance exploration, large social networks, symbolic representation, and innovative technology—were already in place 20,000 to 40,000 years earlier than believed. That coincides with the age of the earliest known human fossils, recently found elsewhere in Africa. “What we’re seeing in Olorgesailie is right at the root of Homo sapiens,” Potts says. “It seems that this package of cognitive and social behaviors were there from the outset.”

“They demonstrate human ways of thinking and doing that cannot be traced easily in the remains of our skeletons or genes,” says Marlize Lombard, an archeologist at the University of Johannesburg. “They provide strong indicators that by about 300,000 years ago we were well on our way to become modern humans in Africa.”

It’s a “textbook example of good archaeological practice,” adds Lyn Wadley from the University of Witwatersrand.

For the longest time, most of the tools that were uncovered at Olorgesailie were Acheulean handaxes—large, teardrop-shaped tools made by chipping away at cores of stone. Hominids like Homo erectus used these implements to butcher meat and cut wood. At Olorgesailie, they started doing this 1.2 million years ago, and continued until at least 500,000 years ago. And during all that time, the basic design of the axes changed very little. In an age where the phones in our pockets can become obsolete in a year, “the idea of a single technology lasting that long is almost inconceivable,” says Potts.

Acheulean hand axes did eventually go obsolete, giving way to the tools of the Middle Stone Age. These were smaller, more carefully shaped, more specialized, and more varied. Instead of just bulky axes and cleavers, they also included spear tips, scrapers, and awls. Potts’ team started finding these at Olorgesailie in the early 2000s, and Alan Deino from the Berkeley Geochronology Center worked out how old they are by analyzing levels of radioactive isotopes of argon and uranium in the samples. He concluded that these tools had completely replaced the Acheulean designs by at least 305,000 years ago.

Many of the tools were made from a black volcanic rock called obsidian, which was brought to the site and processed there. But from where? There aren’t any obsidian outcrops near Olorgesailie. The chemistry of the tools suggests that they came from sources up to 100 kilometers away. But “these are straight-line distances that, in some cases, go over the top of a mountain,” says Alison Brooks from George Washington University.

It’s unlikely that the residents of Olorgesailie regularly commuted to get their obsidian. Instead, they probably took part in long-distance trade networks, receiving obsidian from people who lived in distant locales presumably in exchange for other goods. “There’s an occasional piece in the Acheulean that gets transported these distances,” says Brooks. “But we have thousands of pieces in this one site that’s smaller than most people’s kitchens. There has been a really major import of raw materials.” If she’s right, then Olorgesailie’s obsidian network precedes other examples of long-distance trade by 80,000 to 100,000 years.

These networks help to explain another Olorgesailie discovery: colored rocks. One site contains 86 rounded lumps of manganese ore, which would have produced dark brown or black pigments. Another harbored two lumps of iron minerals that had clearly been deliberately ground with some sharp, chiseling tool to extract the red powder within. “Mixed with any kind of fat, or even rubbed on oily skin, it would have made a very wonderful paint,” says Brooks. “Pigments are often seen as the root of complex symbolic behavior,” says Potts. “Think of the way we use color on clothes, flags, and tattoos—all signals of social identity.”

As evidence for symbolic behavior, Brooks would give this a six on a scale of one to 10, where 10 would be something unambiguous like ochre-covered beads or cave art. Still, she notes that the colored rocks, like the obsidian, came from distant sources, which says something about their value. “Why go through all the trouble of importing pigment?” she says. “If you’re thinking about a way to signal at a distance that you’re not an enemy, having something red on your person is a good way to do it.”

“These findings mark a step forward in our understanding of the origin of complex cultures,” says Daniela Rosso from the University of Bordeaux. She notes that archeologists have found evidence of pigment use in sites from France, Kenya, and the Netherlands, all of which have been dated between 250,000 and 300,000 years ago. The Olorgesailie specimens, once again, are even older, and the earliest known examples of clearly worked pigments.

In fact, some of the innovations that the team discovered were evident even earlier. Between 500,000 and 615,000 years ago, Acheulean technology still dominated at Olorgesailie. But there are occasional signs of smaller tools, more sophisticated designs, and materials being imported from long distances. “In the late Acheulean, we see the precursors of what became crystallized in the Middle Stone Age,” says Potts. It’s almost as if humanity already had the capacity for our later leap, but were missing some kind of trigger—something that precipitated a break with hundreds of thousands of years of cultural stagnation. But what?

The animal bones at Olorgesailie provide a clue. When people were still making Acheulean hand-axes, the landscape was dominated by large grazing mammals like elephants and giant baboons. But by the time the Middle Stone Age tools appear, 85 percent of these species have disappeared, and are replaced by smaller ones like springbok. “This shows that there’s something bigger going on than just changes in the hominins,” says Potts. “The hominins are responding to something, as are the rest of the mammals.”

By analyzing the sediments at the site, Potts found that its cultural shifts took place at a time of—quite literally—great upheaval. Around 500,000 years ago, the relatively stable lake basin at Olorgesailie turned into an etch-a-sketch landscape that was continuously remodeled by earthquakes. By 360,000 years ago, the climate had become incredibly unstable, with big swings between dry and wet seasons, and large changes in the layout of rivers, lakes, and floodplains.

Perhaps it’s no coincidence that this was the world in which modern human adaptability arose—one of unpredictable weather and unreliable resources. Brooks has shown that modern hunter-gatherers also build larger networks in times of environmental turmoil. “It spreads the risk over a much wider landscape,” she says. “There’s no other way they can save for a future disaster. They don’t have crops or animals. They have friends. It’s part of a human way of life.”

“In view of this, the movement of stone and pigments could indicate increased interaction with immediately surrounding groups,” says Polly Weissner, an anthropologist at the University of Utah. And perhaps these broader networks ignited the development of new technology, allowing the culture to ratchet up from the longstanding Acheulean tradition into something more advanced.

“Could these sorts of behaviors been the leading edge of the origin of our species?” asks Potts. The old view says that Homo sapiens evolved complex cultures a long time after becoming a distinct species. But given the antiquity of the Olorgesailie finds, Potts now wonders if the emergence of complex behavior was “really the thing that distinguished the earliest members of our gene pool from other hominins?” Brooks agrees. “There was the argument that Homo sapiens came along and then developed all these things,” she says. “But now it seems that the behavior and the morphology came along together. Maybe the behavior even came first.”

“To my knowledge, the Olorgesailie studies document the context at the dawn of our species in much greater detail than any other early Middle Stone Age occurrence on the continent,” says Yonatan Sahle from Tubingen University. But he cautions that the emergence of the Middle Stone Age “was neither straightforward nor uniform across space and time.” In different parts of Africa, it varies in when it first appears, how much it overlaps with the older Acheulean tech, and whether it occurs together with Homo sapiens fossils.

Indeed, “there’s a tendency for archeologists to say that every important thing happened at my site,” says Potts, “and I don’t want to mislead and say that the Middle Stone Age originated in Olorgesailie. What’s going on there is simply representative of these changes in behavior.”

For now, Olorgesailie has nothing to say about a crucial window of time between 320,000 and 500,000 years ago. Earthquakes and erosion have destroyed the artifacts from this period, which is also when the local fauna and climate changed so radically, and when the local hominins started behaving differently. “It’s that period everyone should be looking at,” Potts says. “And we have data coming that fills in that gap.”