Nature

Nature

Nature

Nature

Scientists have unveiled an extraordinary new analysis of thousands of stone tools found at a site called Attirampakkam in India, northwest of Chennai in Tamil Nadu. Thanks to new dating techniques, a team led by archaeologist Shanti Pappu determined that most of the tools are between 385,000 and 172,000 years old. What makes these dates noteworthy is that they upend the idea that tool-making was transformed in India after an influx of modern Homo sapiens came from Africa starting about 130,000 years ago.

According to these findings, hominins in India were making tools that looked an awful lot like what people were making in Africa almost 250,000 years before they encountered modern humans. This is yet another piece of evidence that the "out of Africa" process was a lot messier and more complex than previously thought.

Pappu worked out of the Sharma Centre for Heritage Education in Chennai with a team of geoscientists and physicists to date the tools. They used a technique called "post-infrared infrared-stimulated luminescence," which measures how long ago minerals were exposed to light or heat. In essence, it allows scientists to determine how long ago a tool was buried and hidden from the Sun's heat, and it uses that information as a proxy for the tool's age.

Writing in Nature, the group explains that the Attirampakkam site is ideal for this kind of dating, because it was regularly flooded by a nearby stream, meaning that discarded tools were quickly covered up by sediments in the water. Those regular floods left behind a relatively tidy stack of debris layers, each of which could be dated.

To their surprise, Pappu and her colleagues found that this region—once a tree-shaded shoreline, ideal for long-term camping—had been occupied by early humans for hundreds of thousands of years. Partly that's because the river carried great heaps of quartzite rocks and pebbles to the area. Quartz was the preferred stone for tools, and it's obvious that this place was a tool workshop. Alongside axes, knives, projectile points, and scrapers, the team found half-finished tools and discarded flakes created by chipping away at a rock to make a blade.

The Middle Paleolithic toolbox

But here's where the story gets weird. The hominins who made tools at Attirampakkam made a wide variety of items, some of which closely resembled the Middle Paleolithic style that emerged in Africa around 300,000 years ago. The Middle Paleolithic marks a cultural shift when humans began to make smaller, more complicated tools, often requiring toolmakers to shape their stones in a multi-stage process. Before the Middle Paleolithic, hominins created biface tools, or simple, heavy hand axes shaped like teardrops.

A traditional "out of Africa" hypothesis holds that early humans in India were essentially stuck in the biface age, making their elementary axes until modern Homo sapiens swarmed the subcontinent about 130,000 years ago and brought the wonders of Middle Paleolithic tools to everyone. Except Pappu and her team found a mix of bifaces and Middle Paleolithic tools at Attirampakkam. Somehow, African and Indian hominins were developing the same toolmaking skills at roughly the same time.

This changes our understanding of human development and ancient migration patterns. There is no doubt that a massive number of modern humans poured out of Africa about 100,000 years ago. But they weren't necessarily as important to global cultural development as we might think.

It's possible that hominins from Africa started traveling to India almost 400,000 years ago, bringing new ideas about tool technologies along with them. Pappu and her colleagues point out in their paper that the Attirampakkam site was active during at least two periods when the climate would have allowed easy crossing from Africa to Eurasia, through a transcontinental jungle rich with food and other resources. Of course, it's also possible that the Middle Paleolithic tools at Attirampakkam are an example of convergent evolution, where two separate cultures hit upon the same innovations at roughly the same time.

Which humans?

We don't have enough evidence yet to say which hypothesis is more likely, but Pappu's research is yet another hint that modern Homo sapiens culture was evolving outside Africa as well as within it. Also, we have to use the designation "Homo sapiens" carefully here. Pappu and her team note in their paper that only one archaic human fossil, the Narmada cranium, has ever been discovered in India. That leaves plenty of gaps in the record.

Attirampakkam is strewn with the results of human productivity, but there are no fossils to tell us who these humans were. An early ancestor, like Homo erectus or the Narmada human? Possibly Neanderthals or Denisovans, who were both roaming Eurasia at the time? Some hybrid we've yet to discover?

Regardless of who these early humans were, it's certain that they were already engaged in modern human toolmaking before Homo sapiens arrived from Africa. What's fascinating about the Attirampakkam site is that the evidence suggests that the people there may have started migrating en masse at the same time Africans did. In the most recent layers of the site, tools become sparse. Humans were coming to this place less and less often. The people of Attirampakkam may have fled climate fluctuations caused by the Toba eruption 70,000 years ago, or they may have been responding to other changes.

Pappu and her colleagues write that, ultimately, the remains at Attirampakkam aren't just testimony to human innovation. They are also a sign of "placemaking," a cognitive shift that made humans want to return to the same location, generation after generation. We're seeing the emergence of collective memory and historical knowledge right alongside the development of sophisticated stone tools.

Nature, 2018. DOI: 10.1038/nature25444 (About DOIs).

Listing image by Pappu et al. / Nature