Human evolution: a last archaic hominin stronghold in India

Scientists trace the evolution and migration of ancient hominins to the edges of India

Human history can be characterised perhaps by one skill above all else: the ability to make tools that vastly expand our technological abilities. In fact, for scientists tracing the fascinating, branching tree of human evolution, non-perishable stone tools provide a priceless window into the past.

The Acheulean is the name given to the longest-lasting tool-making tradition in history; Acheulean hand-axes and cleavers emerged around 1.5 million years ago in Africa, and persisted in Eurasia until just a few hundred thousand years ago, made by our ancestral and cousin species, like Homo erectus and, later, Neanderthals.

Scientists have been able to trace the evolution and migration of ancient hominins by mapping the occurrence of these crafted hand-axes around the world; now, new evidence suggests one of the Acheulean culture’s final strongholds was at the edges of the monsoonal region of modern-day India.

The new study, published in the journal Scientific Reports and led by researchers at the Max Planck Institute for the Science of Human History, Germany, re-examined ancient stone tools unearthed at a site called Singi Talav, in Rajasthan, and found that they were used by some of the last creators of Acheulean stone tools in the world, dating to around 177,000 years ago – just before the earliest expansions of Homo sapiens across Asia.

Singi Talav is a set on a lakeside close to the modern town of Didwana, on the edge of the Thar Desert. It was first excavated in the early 1980s, and was long assumed one of the oldest Acheulean sites in India. But, armed with modern dating techniques, the researchers used luminescence to determine the age of the sediments in which the tools were found, disproving earlier theories.

“The lakeside setting has ideal preservation conditions for an archaeological site, enabling us to return 30 years after the first excavation and readily re-identify the main occupation horizons again,” says Jimbob Blinkhorn of the Max Planck Institute, lead author of the study.

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“We’ve applied a range of modern methods to re-examine this critical site, including new approaches to directly date the occupation horizons and to reveal the vegetation in the landscape that Acheulean populations inhabited.”

“Ours is the first study to directly date the occupation horizons at Singi Talav, enabling us to understand both when ancient humans lived here and created the stone tool assemblages, and how these occupations compare with other sites across the region,” adds co-author Julie Durcan, of the University of Oxford.

On the margins of the monsoon

The Thar Desert, where these last Acheulean toolmakers held out, is at the western edge of India’s summer monsoon system; it’s a fluctuating landscape of wild extremes, and its habitability will have varied across time.

In order to piece together the landscape these early hominins would have known, the researchers examined plant microfossils, also known as phytoliths, and features of the soil’s geochemistry.

“The results from the two methods we applied complement each other to reveal a landscape rich in the types of grasses that flourish during periods with enhanced summer monsoons,” says Hema Achyuthan, of Anna University, Chennai. These conditions would have helped the population flourish.

“This is the first time the ecology of an Acheulean site in India has been studied using these methods, revealing the broader character of the landscape that these populations inhabited,” Achyuthan adds.

When hominins meet

The researchers say that these remnant Acheulean populations are some of the last strongholds of their material culture in the world.

“This supports evidence from across the region indicating that India hosted the youngest populations using Acheulean toolkits across the world,” says Blinkhorn.

“Critically, the late persistence of the Acheulean at Singi Talav and elsewhere in India directly precedes evidence for the appearance of our own species, Homo sapiens, as they expanded across Asia.”

It suggests that, just maybe, these rich monsoonal grasslands could have hosted a chance encounter between two cousin species, one that had clung on for hundreds of thousands of years, and another whose expansive journey was just beginning.