This is how hominins adapted to a changing world 2 million years ago

January 8, 2021 by No Comments

The versatility that helped humans take over the world emerged very early in our evolutionary history, according to sediments and stone tools from Olduvai Gorge in Tanzania.

Olduvai has provided some of the oldest known tools and fossils from our genus, Homo. A recent study lines that evidence up with environmental clues buried in the sediment. The results suggest that our early relatives were equipped to adapt to new environments by around 2 million years ago.

That seems to have been a key ability that allowed our relatives to go global. By 1.7 million years ago, an early human relative called Homo erectus had spread beyond Africa and throughout most of Asia, as far as Indonesia. They had reached western Europe by 1.2 million years ago. Along their travels, the hominins encountered environments very different from the ones their ancestors had evolved in, like the tropical forests of Indonesia and the arid steppes of central Asia.

They may have been able to prepare for that simply by staying in one place within Africa. At Ewass Oldupa, a recently excavated site on the edge of the famous Olduvai Gorge, findings indicate that early hominins lived in a constantly shifting landscape.

Life after the volcano

The oldest evidence we have for early human relatives at Olduvai Gorge is a handful of stone tools, made and used around 2.03 million years ago.

Like the other tools unearthed at Ewass Oldupa, they’re part of the Olduwan complex: relatively simple stone tools made by early hominins like H. erectus and H. habilis. Olduwan tools are mostly sharp flakes and very basic tools for chopping, scraping and pounding. They’re much less complex and precise than the tools made by later hominins, like Neanderthals, who chipped small flakes off carefully prepared stone cores. But for a few hundred thousand years, the rough-and-ready Olduwan tools got the job done.

At Ewass Oldupa, the job was survival in a landscape of mostly bracken fern meadows dotted with a few grasses and woody plants, watered by a meandering river. The ferns were probably the first plants to put down roots atop the wide fan of pumice that had spewed from a nearby volcano not too long beforehand. Traces of that landscape are still buried in a layer of sediment about a meter above the rocky remains of the ancient pyroclastic flow; paleoanthropologist Michael Petraglia, of the Max Planck Institute for the Science of Human History, and his colleagues found fossilized pollen and microscopic pieces of fossilized plant tissue called phytoliths in the layer, alongside 10 stone tools.

For hunter-gatherers like H. habilis, whose fossilized remains have been unearthed just a few hundred meters away from Ewass Oldupa, the ferny basin would have been a pretty good place to make a living.

The river offered ready access to water, and the geology of the area provided several sources of stone for tools. Geochemical analysis of the tools at Ewass Oldupa suggest that hominins here gathered some of their quartzite locally and ventured up to 12 kilometers (7.5 miles) away for the rest. They seemed to choose different materials—in some cases as specific as choosing slightly different types of quartzite from different outcrops—for particular tools. (A study last year also suggested that the earliest toolmakers in our family tree knew enough to choose their materials wisely.)

But then, as it always does, everything changed.

New worlds in the same place

Thousands of years later, the hominins who had once foraged by the riverbanks wouldn’t have recognized the landscape around Ewass Oldupa. The meadows of bracken had given way to a patchwork of woods and grasslands around the shores of a lake. Microscopic fossils trapped in the sediment suggest that the plant species that made up those woods and grasslands changed often, and deposits of charcoal reveal that wildfires periodically swept through the area, helping the patchwork landscape rearrange itself.

At other points in the area’s long prehistory, the lake expanded, and the muddy sediments of the lakeshore hint at a lush landscape of forests and palm groves. The lakeshore later gave way to a dry steppe, mostly bare of trees and grass. Each of those environments offered wildly different foods, water, supplies, and challenges, but hominins seem to have kept coming back to Ewass Oldupa.

“Over the course of time, these habitats sometimes changed slowly or rapidly,” Petraglia told Ars. “It is difficult to know how quickly hominins entered new ecosystems owing to the resolution of the record, but it is clear that they were able to cope with a wide variety of environments.”

Petraglia and his colleagues found stone tools left behind by hominins who lived at the site (probably H. habilis) off and on throughout its 200,000 years of constant change. The 565 stone tools, scattered across millennia of layered sediment at the site, don’t look like the detritus of a permanent settlement. Instead, it looks like hominins left the basin several times, maybe due to sudden environmental change or volcanic eruptions, but they kept coming back.

“There were a number of volcanic events within the 235,000 year time range represented at Ewass Oldupa,” Petraglia told Ars. “It is interesting that hominins returned to these areas after each of the eruptions—that is, they never entirely abandoned the region.”

Jacks of all trades

And even if the earliest hunters and gatherers at Ewass Oldupa would have found later versions of the place totally alien, they would still have recognized the tools people used to survive it. For roughly 200,000 years, hominins relied on the same basic tools to tackle the bracken meadows beside the river, the patchwork of woods and grassland, the lush lakeshore, and the dry steppe.

The chopping, scraping, and pounding tools of the Olduwan were relatively simple, but they were also incredibly versatile. According to Petraglia and his colleagues, Olduwan technology offered a basic, general toolkit that worked as well in a lakeside palm grove as it did on a dry steppe. Humans took over the world because we’re generalists, and generalists can adapt to nearly anything. Our early relatives clearly had the same advantage.

Nature Communications, 2020 DOI: 10.1038/s41467-020-20176  (About DOIs).

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