The turbulent environment set the stage for a leap into human development and technology 320,000 years ago

People thrive around the world, at every temperature, elevation and landscape. How did man become so successful in adapting to whatever environment we live in? Human emergence researchers like me are interested in how this quintessential human trait, adaptability, evolved.

On a site in Kenya, me and my partner have been working on this puzzle for decades. This is a place where we are seeing major changes in the archaeological and fossil record hundreds of years ago. But those external factors prevented the emergence of behaviors that typify our species, Homo sapiens, Does it interact with its surroundings?

We wanted to know if we could connect technology and these human species to what was happening in the environment at that time. Based on our analysis, published in the journal Science Advances, we conclude that the roots of Homo sapiensEvolutionary adaptation stem from our ability to accommodate environmental change.

Aerial view of the Olorgesailie region today.
Human Origins Program, Smithsonian

Lost time in archaeological record

Map locates site in Kenya
Olorgesailie is in East Africa, in Kenya.
Human Origins Program, Smithsonian

The famous prehistoric site Olorgesailie is in southern Kenya. It is located within the Rift Valley, an increasingly active area where lakes and streams have produced sediments that accumulate over time, burying and preserving fossil bones and ancient stone tools.

At Olorgesailie, our scientific team has found evidence that is possibly related to the origin Homo sapiens As a significant transition from one technology to another.

The old technique is typified by large, oval cutting devices called handaxes. Typical of what is called Inhalian stone technology, approximately two dozen layers of these handaxes and other Acheulean equipment have been unearthed at Olorgesailie. They cover a period of approximately 700,000 years, a time when fossil remains show that hominin species Homo erectus And Homo heidelbergensis Nestled in East Africa.

The last Acheulean archeological site at Olorgesailie is 500,000 years old, at which point there is a dismal 180,000-year difference in these depressions due to erosion. The archeological record resumes about 320,000 years ago, as sediments began to fill in the landscape.

But Aitchin was gone. It was replaced by Middle Stone Age technology, which typically included smaller, more easily included clanchy echulian handaxes. In other areas of Africa, Middle Stone Age technology is associated with the earliest Africans. Homo sapiens.

Acheulean handaxes and Middle Stone Age projectiles and pigments
Acheulian technologies were replaced by the Middle Stone Age, after a 180,000-year hiatus in records at Olgesley.
Human Origins Program, Smithsonian

These device manufacturers often used sharp-edged black obsidian as a raw material. Archaeologists Alison Brooks, John Yellen, and others chemically discovered the far-flung Presidian in many different directions, 95 kilometers from Olegelli. They concluded that far-flung obsidian sources provide evidence of resource exchange between groups, a phenomenon that is unknown in the Aculean period.

Our Middle Stone Age excavations also included black and red colored materials. Archaeologists viewed the pigments in such a way that they were signs of increasingly complex symbolic communication. Think of all the ways that people use color – in flags, clothes, and many other ways that people claim their identity as part of a group.

So here we had Aitchin’s extinction of life, as well as technological innovations, dramatically intergroup exchanges of observations and its new replacement, including the use of dyes. But we had no way to test what happened in the 180,000-year interval when this infection occurred.

We needed to fix that time. We began to speculate on how we could detect nearby depressions that would have quickly led to better adaptation to environmental and survival challenges with this change.

Turning to geology for clues about early humans

Different types of sediment are placed in lakes, streams and soils, and the layers of sediment tell the story of changing environments over time. Geologists Kay Behrensmeyer and Alan Dino joined me in the area in southern Kenya to find out where we could drill for sediment that could fill in the Olergacelli time interval.

We hypothesized that the key to understanding the major change would lie under a flat, grassy plain about 24 kilometers south of our Olegsale excavation. Together with colleagues including René Domán and colleagues at the National Lakesienne Corps facility, we drilled in September 2012, until we reached the volcanic rock floor of the Rift Valley.

Drill team at work in the evening
The drill team pulled out a cylinder of earth, just four centimeters in diameter, representing 1 million years of environmental history.
Human Origins Program, Smithsonian

The result was an ancient 139-meter-deep lake and a sequence of marginal settlements and soils, all submerged by volcanic layers that we could find to create the most accurately dated East African environmental record for the past 1 million years. Could

With the advice of geologist Andy Cohen and other colleagues, I assembled an international team of Earth scientists and paleontologists to sample and analyze the core. We explored ways to change many different measures of the past environment – micro bits of plants, single-celled diatoms from ancient lake deposits and various chemical signals – into ecological measures of freshwater availability and vegetation cover. The newly published study provides our findings.

Environment during time interval

The sedimentary record showed that during the era of 1 million to 500,000 years ago, when Ekhulen toolmakers were busy in the Oleragelis Basin, ecological resources were relatively stable. Fresh water was available reliably. Grazing zebras, rhinoceros, baboons, elephants, and pigs transformed regional vegetation into wild grassland to create small, nutritious grasslands.

And then what happened in the time gap?

Cross-section of core portion
Each sedimentary layer seen in this cross-section of the core provides a clue about the ancient environment.
Lakecore, University of Minnesota

The core is very well preserved in earlier mysterious time intervals. We determined that about 400,000 years ago, a significant environmental transition occurred. From a relatively stable setting, we began to see frequent fluctuations in vegetation, available water and other ecological resources upon which our ancestors and other mammals depend.

According to anthropological literature, hunter-gatherers respond to a period of uncertain resources by investing time and energy to refine their technology today and in recent history. They join distant groups to maintain a network of resource and information exchange. And they develop symbolic markers that reinforce these social connections and group identities.

Familiar? These practices resemble how the ancient Middle Stone Age lifestyle in Olegasale differed from the Aesulian way of life.

Equally notable, the large grazing species that is typical of the Aculean period, went extinct 500,000 years ago. 360,000 and 300,000 years ago, small and tall grasses and tree leaves reduced in size to water-dependent and reliable, ecologically flexible herbaceous species of special types of herds such as zebras and now extinct species of giant baboons Had taken place.

These changes in the animal community reflect the benefits of adaptable diets, a parallel that our Middle Stone Age ancestors adjusted for environmental uncertainty.

Scientists working with the cross-section of a sediment core
Back in the lab, the scientists analyzed the contents of the core’s sedimentary layers.
Human Origins Program, Smithsonian

For the past two decades, researchers of many human origins have thought of climate as the primary, if not the only, driver of hominin adaptive development. Our new study draws attention to several factors of the Achelenian – Middle Stone Age transition in southern Kenya.

Yes, after the environmental transition 400,000 years ago, rainfall strengthened. But the entire area was fractured by tectonic activity and blanketed with volcanic ash. And older vegetarians have different effects on vegetation before and after this infection.

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The result was an ecological fountain of changes involving early humans who practiced the Stone Age mid-life. We propose that all these factors together provoked this important evolutionary change.

The Middle Stone Age may be a lesson for today. As humanity now faces an era of environmental uncertainty on a global scale, is our species agile enough to engage social networks, new technologies and reliable sources of information to accommodate further environmental disruptions Could?

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