Roughly 74,000 years ago, a supervolcano on the Indonesian island of Sumatra roared to life. Known as the Toba eruption, the event was the largest volcanic blast in the last two million years, scattering ash thousands of miles and leaving behind a 60-mile-wide crater that has since filled with water.
Some scientists have argued that the supereruption must have caused a global cold spell, darkening the sky with ash and soot and producing a prolonged period of deforestation in South Asia. If that’s the case, though, the eruption and its aftermath didn’t stop early humans from surviving in central India, scientists report.
At the Dhaba dig site in the state of Madhya Pradesh, ancient tools appear in layers of sediment that date to between 80,000 and 65,000 years ago. According to a new study in Nature Communications, the same types of tools continued being used before and after the eruption, so the study authors assert that one continuous population must have survived the fallout from Toba.
“The big theory out there was that the Toba supereruption created a volcanic winter, so it led to glaciation, it resculpted ecosystems, [and] it had tremendous impacts on the atmosphere and landscapes,” says Michael Petraglia, an anthropologist at the Max Planck Institute for the Science of Human History. But his group hasn’t found evidence for such large impacts to the landscape at the Dhaba site.
“It’s much more subtle than what people had imagined,” Petraglia says. “It doesn’t mean there’s no ecological change, but these hunter-gatherers would have been able to adapt to the changes.”
The study authors believe the artifacts from India match similar tools previously found at sites in Africa, Australia, and the Arabian Peninsula that date to the African Middle Stone Age, about 285,000 to 50,000 years ago. Given the similarity between these tool technologies, the team suggests that the site offers yet more evidence of Homo sapiens moving out of Africa earlier than previously believed.
Hints of early migrations
Genetic evidence suggests modern humans are the descendants of a wave of Homo sapiens that left Africa sometime between 80,000 and 50,000 years ago, although other populations remained in Africa. But fossils found in present-day Israel that appear to be modern humans date back more than 120,000 years. Such findings have led researchers to search for more clues about when smaller groups of humans might have left Africa.
When Petraglia went to India nearly 15 years ago to search for evidence of early humans’ migrations, he expected to find artifacts from the Upper Paleolithic—stone tools similar to those used by Homo sapiens in Europe around 45,000 years ago. Instead, his team uncovered much older stone tools at Dhaba, suggesting early humans trekked thousands of miles from Africa to India earlier than expected.
The new study provides further evidence against the once-popular belief that the Toba eruption decimated human populations and halted migrations around the world, says Jayne Wilkins, an anthropologist at the Australian Research Centre for Human Evolution at Griffith University who was not involved in the research. A 2018 study similarly showed continuous tool use in South Africa around the time of the Toba eruption, and this site in India is about 3,000 miles closer to the volcano than South Africa—so conditions may have been significantly more challenging for survival.
“Data from new archaeological sites like Dhaba are showing that by 74,000 years ago, early hunter-gatherers were resilient in the face of major climatic events, aided by complex technologies, social networks, and other sophisticated cultural adaptations,” Wilkins says in an email.
“Whether this is exactly the same population or not could be debated, but based on the available information, it’s a reasonable suggestion.”
Shards of doubt
However, other experts are more critical of the study’s conclusions.
“I’m not excited about this paper,” says Stanley Ambrose, an anthropologist at the University of Illinois who has been studying tool technologies, geology, and human evolution since the 1980s. Ambrose collaborated with Petraglia on a 2010 study of tools excavated in southern India, which also suggested continued habitation after the eruption, and he authored a paper in 1998 suggesting Toba may have had an impact on the evolution of Homo sapiens.
“I’ve got Toba ash in my lab, in the creases of my boots, in my mind,” Ambrose says. “I’m quite familiar with the location.”
He points out that the authors only found six tiny glass shards matching the chemical signature of the Toba eruption, while there were far more volcanic shards found 5,000 miles away in South Africa. The shards at Dhaba, or even the tools, could have been carried to the site by the Son River or other geologic processes, he says.
“You can’t call it an archaeological site. You can call it a geological site that has archaeological artifacts in it,” Ambrose says. He also isn’t convinced that the tools found at Dhaba were made by early modern humans, especially because no one has found human fossils from the same time period near the tools.
“It takes close, careful forensic scrutiny and tedium to show that this is what the evidence actually shows,” he argues.
Petraglia counters that the ash fragments support the dates calculated for the sediment layers and provide additional evidence that the stone tools overlap with the Toba event, but the study team does acknowledge that the glass shards could have been carried in from nearby sites. He adds that this population from India didn’t necessarily contribute genes to modern human populations; they may well have died out or been replaced by later migrations.
“We don’t dispute the fact that there was an increase in modern humans after 60,000 years ago,” Petraglia says. “What we are arguing is the idea that modern humans only spread out of Africa once is wrong.”