What the hell are these? thought Rick Potts. The Smithsonian paleoanthropologist was looking at a small, round, coal-colored lump. The stubby rock was accompanied by another 85, all excavated at the site of the Olorgesailie Basin in southern Kenya.
Over the past decade, the site has revealed a large number of findings to Potts and his team of Smithsonian researchers and the National Museums of Kenya, which includes thousands of tools made by hominins, fossilized mammalian remains and sediment samples that span hundreds of thousands of years. But the lumps were a mystery.
Back in the laboratory, the researchers badyzed them to discover that they were black pigments: the oldest paleocrystals that have been discovered, dating from about 300,000 years ago.
That was just the beginning of the intrigue. Having studied this site and this period in human evolution for a long time, Potts knew that primitive humans generally obtained their food and materials locally. However, these "crayons" were clearly imported. They had formed in a brackish lake, but the nearest body of water that fit that description was about 18 miles away. That was much further than most of the inhabitants would have traveled regularly, given the uneven terrain. So, what was happening?
The pigments, Potts and his coauthors now believe, were part of a prehistoric commercial network, one that existed 100,000 years earlier than scientists previously thought.
In addition to the pigment lumps, the researchers point to the transformation in stone tool technology as proof of this claim. On the same site, they found thousands of newer tools made of materials that had been transported over long distances. report these findings in a series of three related documents published today in Science; in addition to Potts lead authors include Alan Deino a geochronologist at the University of California at Berkeley, and paleoanthropologist Alison Brooks at George Washington University.
"The earliest evidence from Homo sapiens in East Africa is from about 200,000 years ago, so this evidence from the Stone Age is significant before that," says Potts, who is the director of the Human Origins Program at the National Museum of Natural History and has led the Olorgesailie research for more than 30 years. "[Early humans] were rare in their environment, based on the fossil record itself, but they left behind these durable business cards, these stone tools, so we know much more about the transition in behavior than time or who they really made these tools. "
These complex behavioral changes signal a major shift in cognition, which may have given modern humans an advantage over other hominin lineages out there. The researchers even offer a possible explanation for the change: environmental instability. By examining the markers of change in the environment, researchers find that this profound cognitive leap occurred at the same time as dramatic transformations in climate and landscape.
The transition in question in Olorgesailie extends from 500,000 years ago to 300,000 years ago. At the beginning of that change, the dominant hominid was Homo erectus the earliest known older humans that appeared about 1.8 million years ago and spread throughout the world. The "straight man" is often accompanied by the hand ax, a stone tool that has been discovered in places in Africa, Asia and Europe. Pear-shaped stone tools belong to a technological tool tradition known as Acheulean, which lasted more than a million years.
But about 500,000 years ago, these axes began to look a little more refined, says cognitive archaeologist Derek Hodgson of York University, who was not involved in the new research. "You get three-dimensional symmetry in handaxes, as if hominids could rotate the object in the eye of the mind, which is a very complex ability to achieve," says Hodgson. "These tools seem too refined, and some are too big for functional needs." In other words, these later tools could have been used to indicate social status or for aesthetic reasons.
Potts and his team at Olorgesailie also observed this evolution in handaxes. What began as strictly functional tools made of local stone were gradually infiltrated by smaller, occasional tools and transported materials. 300,000 years ago, the transition in Olorgesailie was complete. Handaxes had essentially disappeared, leading to a new technological age called the Middle Stone Age, and a new type of hominid wielding those smaller tools.
When and why this change happened, and who was behind it, has been debated for years. The challenge in the past has been the lack of registration. "The attempt to pinpoint the timing and circumstances of this process suffers from a series of conceptual and practical difficulties," archaeologists Sally McBrearty and Christian Tryon write in a 2006 article . Namely, archeologists have never been able to find archaeological sites with continuous layers of sediment covering that transition, probably because the Rift Valley suffered enormous tectonic interruptions.
The sediments of the Olorgesailie Basin suffer from the same vacuum that is missing, which extends from 499,000 years ago to 320,000 years ago. What happened in those mysterious years is still in debate. But what emerged from the other side in Olorgesailie is something never before seen at such an early date: humans who had the social and cognitive skills to create refined tools; long-distance commercial networks to obtain optimal materials for the manufacture of tools, such as obsidian; and the ability to adapt to survive in an environment that included earthquakes, volcanoes and fluctuating wet and dry cycles.
The tools themselves stimulated the neurological change, or did the larger brains of Homo heidelbergensis -who usurped the throne of the hominids of Erectus and is believed to be the shared ancestor of Homo sapiens and the Neandertals – allow the creation of these new tools? It is a query that the physical remains can not answer at all. "It's as if humans were really smart before there were computers," says Potts. "It's a great invention, and yet, obviously we're the same people as before the computers that later"
Hodgson agrees that neural networks probably had to be in place for the creation of new tools, and perhaps those neural networks were also related to new social behaviors such as commercial alliances and the use of pigments. But understanding the relationship between humans and their unpredictable environment remains a crucial piece of the puzzle.
The Great Rift Valley is named for its location on top of an intracontinental ridge system that has been tectonically active for millions of years. During the transition that the team was studying, there was also a movement to a drier environment with moisture intervals . Animals, plants and landscapes changed: examining the fossil record of fauna, Potts and his team discovered that 85 percent of mammal species experienced local extinction during that transition between the Acheulean and the Middle Stone Age.
These environmental challenges may have pushed humans towards greater cooperation and exploration. "If it had been every hominid by itself, it would have been a disaster, and that could have been one of the reasons why the Acheulean way of life disappeared," says Potts. Perhaps that is why the peoples of the Middle Stone Age in Olorgesailie obtained 50 to 60 percent of their toolmaking materials: they used the trade as a means of survival.
It's an intriguing narrative, but researchers still need to fill in the gaps in the geological record to verify it. Which is exactly what's on the horizon for Potts, and for paleogeologists like Andrew Cohen, professor of geosciences, ecology and evolutionary biology at the University of Arizona who worked with Potts in the past. Cohen leads the Paleolakes and Hominino Sites Drilling Project and has presented works based on core samples from the region, which will further clarify our knowledge of local climatic fluctuations.
"The finding of a fairly continuous record of Late Acheulean in Middle Stone Age is a spectacular find," says Cohen of Potts' work. "Trying to reduce the moment of transition is a big step forward." Expect to continue with the next step with much more detailed climate records for the same time and in the same place.
This type of research does more than help us understand where we come from. Studying these milestones in humanity's past, says Cohen, could help us prepare for a future in which the Earth's climate is once again unpredictable. "We have 10 or maybe more hominid species, and they all went extinct for reasons we do not understand," says Cohen. "I think it's imperative that we try to understand them, it's not just an evolutionary event, but also extinction events."