Did prehistoric climate change help make us human?

Human Origins Program/Smithsonian/File
Scientists at the University of Minnesota's Olorgesailie Drill Core Workshop work to reconstruct key features of the ancient landscape and climate across time in the East African Rift Valley, in November 2015.
  • Quick Read
  • Deep Read ( 4 Min. )

Piecing together early human history is often like assembling multiple puzzles without all the pieces in the boxes. Researchers do their best to imagine the whole picture from some fragmentary fossils, artifacts, and what environmental data they can gather from the geologic record. But big questions remain about the origins of our species.

One of these arose in southern Kenya, when researchers found that a crucial 180,000 years was missing from the archaeological record at that site. Over that time, stone tool technology leaped from hand axes to a suite of more advanced technologies. 

Why We Wrote This

News of climate change sparks concern, but it also brings out humanity’s most prominent trait: the ability to innovate. One recent study suggests that this was as true in our distant past as it is today.

To better understand that transition, the team turned to the environmental puzzle pieces. Their results, detailed in a paper published in the journal Science Advances on Wednesday, reveal a particularly turbulent period, with rapid changes throughout the environment. And this could yield clues to some of the broader questions about the origins of our species.

“We’re really looking at the foundation of how humans adjust to environmental disruption,” says Rick Potts, study lead author and director of the Human Origins Program at the Smithsonian’s National Museum of Natural History.

For years, Rick Potts has excavated ancient stone tools in southern Kenya, at a site called Olorgesailie, seeking to piece together a picture of what life was like for early humans who lived there. But he and his colleagues were puzzled by what seemed to be a technological leap forward.

Dr. Potts, the director of the Smithsonian National Museum of Natural History’s Human Origins Program, said that the site yielded hundreds of thousands of years’ worth of stone hand axes, suggesting its residents were prolific toolmakers. But those tools seemed to disappear 500,000 years ago, and the next 180,000 years of the archeological record were missing, swept away by erosion. 

The next tools show up in sediments that are some 320,000 years old, and those tools seem to indicate a cultural leap, one that could add to the story of the origins of our species.

Why We Wrote This

News of climate change sparks concern, but it also brings out humanity’s most prominent trait: the ability to innovate. One recent study suggests that this was as true in our distant past as it is today.

But what prompted this leap? With no clear transition in the archaeological record at Olorgesailie the research team was left puzzled.

Dr. Potts and his colleagues found a spot about 15 miles away in the nearby Koora basin where they could extract a core of sediments from deep in the ground to assemble a timeline of the environmental conditions for the last million years.

“And it turns out that the missing time, that 180,000 year gap, is beautifully recorded in the core – thank goodness,” says Dr. Potts.

As the core revealed, a lot happened in those 180,000 years. Beginning about 400,000 years ago tectonic activity fractured East Africa’s landscape into small basins, the landscape alternated between arid grasslands and fertile woodlands. Large herbivores died out, replaced by smaller mammals with diverse diets.

Human Origins Program/Smithsonian
A Nairobi company drills in the Koora basin, extracting a 139-meter sediment core from deep in the Earth. That cylinder of sediment, just four centimeters in diameter, turned out to represent 1 million years of environmental history.

And human behavior changed, too, says Dr. Potts, connecting the technological transition to the ecological context. ”We’re really looking at the foundation of how humans adjust to environmental disruption,” he says. And, according to a paper published by Dr. Potts and the research team on Wednesday in the journal Science Advances, that rapid climate change might explain what drove those early humans to innovate.

Emerging humanity

Piecing together early human history is often like assembling multiple puzzles without all the pieces in the boxes. Researchers do their best to imagine the whole picture from some fragmentary fossils, artifacts, and what environmental data they can gather from the geologic record. But big questions remain.

One of these is how the world went from having several human species – members of the genus Homo – to just one, Homo sapiens. Why did our species survive when others did not? 

While this new study does not point directly to the origin of our species (the oldest fossil found with H. sapiens features has been dated to around 315,000 years ago), it might still provide some pieces of the puzzle.

The artifacts unearthed at Olorgesailie from around 320,000 years ago are markedly different from the earlier artifacts in a way thought to be emblematic of the technology and culture of more modern humans. 

First, while the ancient stone hand axes were large and fairly uniform in shape, likely used for multiple purposes, the newer tools were smaller and more diverse. Some appeared to be projectile points. Others, blades or flake tools. 

Human Origins Program/Smithsonian
Hand axes recovered at Olorgesailie suggests that early humans at relied on the same tools for 700,000 years.

What’s more, while the older tools were made from stones that could be found nearby, some of the newer ones were made of rocks like obsidian that had to have been imported. This, the researchers posit, suggests that the humans at Olorgesailie had begun to engage in long-distance trade with other groups. 

And that’s not all. There’s also evidence that the Olorgesailie residents were using pigments, which anthropologists often take as a sign of symbolic communication. 

“All of that contributes to this strong impression that they are using their landscape and the resources available in it in a much more sensitive way, they’re not doing the same thing all the time,” says Julia Lee-Thorp, emeritus professor of archaeological science at the University of Oxford. “It is a feature of humans that they were using material culture to exploit the resources that were available to them.”

Lessons for the future?

But does that mean this new paper is providing pieces that fit in the puzzle of the origin of our species, H. sapiens?

Perhaps. This turbulent, rapidly changing environment was likely “the crucible from which modern humans sprang,” says Professor Lee-Thorp, and it’s certainly a driver of human evolution.

Still, cautions Pamela Willoughby, chair of the department of anthropology at the University of Alberta, there are instances in the archaeological record where technology seems to leap forward for a bit of time but then return to older styles of tools, or doesn’t change across the landscape as it does in a single site. 

“I think this is a fascinating case study,” she says. “It involves lines of evidence from just about every source that you can get” with a massive, interdisciplinary research team behind it. But it remains to be seen whether these patterns appear across Africa at that time, Dr. Willoughby says.

However, most researchers agree that there’s something about the ability to be flexible in the face of change that seems to set H. sapiens apart. 

“This is kind of defining in ancient times how our species adapts, how it adjusts to times of environmental disruption, or the shift from more stable, reliable times, to times of uncertainty,” Dr. Potts says. 

And, as we enter another period of global climate instability, these findings may inform humanity’s response. 

“The question is, does this work in the face of nation-states?” Dr. Potts asks. “Does it work in the face of big institutions? Does it work in the face of all of those things that have developed in civilization during a period of thousands of years of relative stability in our ecosystems and environment, which are now becoming disrupted?”

With so many more humans living across the entire world in a truly globalized society, Professor Lee-Thorp says, “It’s a very different situation” today than it was in ancient times. “But one would have to hope that human ingenuity would be able to get its head around it, and do something about it. Otherwise we’re in deep doo-doo.”

You've read  of  free articles. Subscribe to continue.
Real news can be honest, hopeful, credible, constructive.
What is the Monitor difference? Tackling the tough headlines – with humanity. Listening to sources – with respect. Seeing the story that others are missing by reporting what so often gets overlooked: the values that connect us. That’s Monitor reporting – news that changes how you see the world.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to CSMonitor.com.

QR Code to Did prehistoric climate change help make us human?
Read this article in
QR Code to Subscription page
Start your subscription today