Ancient Stone Tools Found in Tamil Nadu Push Back ‘Out of Africa’ Exodus Date

A recent discovery in Israel pointed to the possibility that modern humans migrated out of Africa 180,000 years ago. But stone tools unearthed in Attirampakkam have been found to be 385,000 years old.

It has been thought that the Indian Middle Palaeolithic culture developed 90,000-140,000 years ago and was closely tied to the dispersal of modern humans from Africa. But tools excavated from Attirampakkam, Tamil Nadu, have now pushed the antiquity of this culture by almost 50,000 years.

The tools bear marks of the Levallois technology that has its roots in Africa and predates the arrival of modern humans in India.

“These findings spark a new debate about the origins of the Indian Middle Palaeolithic culture,” according to Shanti Pappu, the founder/secretary of the Sharma Centre for Heritage Education (SCHE), as told to The Wire.

The timeline of human history has been, and is, constructed by piecing together evidence from genetic, anthropological and archaeological studies. Among the various types of artefacts, stone tools provide the more concrete evidence of the whereabouts of our ancestors as they journeyed through space and in time.

At the beginning of the Stone Age, early hominins used simple stone tools to gather food from trees and for hunting. As our species evolved and developed abstract thinking, our tool-making technology became more sophisticated. Gradually, modern humans in Africa found new ways of shaping rocks into useful instruments.

“There is a clear difference between the techniques used by hominins to fashion their tools and the knapping technology that evolved over time,” Pappu, also the corresponding author of the new study, explained.

Complex design

Most early Stone Age tools were made by splintering rocks with either a hard stone or antler/wood hammers. The detached flakes would then be shaped into tools of different kinds, like scrapers or hand-axes.

In the Middle Palaeolithic period, a new technology called Levallois became common for forging instruments. “The technique involves the removal of small flakes or points from carefully prepared cores in a structured manner,” Pappu said. The geometric complexity of the process is thought to be a testimony to abstract thinking; some scientists even associate it with the Homo sapiens.

By examining stone tools from Attirampakkam, a village located about 65 km west-northwest of Chennai, Pappu and colleagues have shown how the Indian Middle Palaeolithic emerged from the preceding Acheulean culture around 385,000 years ago and then tracked its subsequent evolution until around 172,000 years ago.

“What’s special about the new tools found at Attirampakkam is that they are complex in design and bear the markings of technologies used by Middle Palaeolithic cultures,” Pappu said. “This implies that groups of humans consistent with this culture started dispersing from Africa (possibly) much earlier than what we believe.”

But apart from being one of the oldest known sites for lithic records, artefacts recovered from Attirampakkam are also significant because of the site’s location.

The Indian subcontinent (not just India) lies between East Africa, Dmanisi in Georgia and Sangiran in Southeast Asia. These regions contain paleoanthropological records – in the form of fossils or stone artefacts – dating back to 1.8 million years or earlier. Ergo, Attirampakkam must have been at a biological or technological crossroads as humans evolved and dispersed.

“That way, the palaeoanthropological record of this region is critical for linking the earliest evidence found in the regions of the Old World (East Africa, Georgia and Southeast Asia) while understanding hominin evolution and adaptations,” Parth Chauhan, an assistant professor of humanities at the Indian Institute for Science Education and Research, Mohali, told The Wire. Chauhan was not involved in the study.

Luminescence dating

Excavation at Attirampakkam began in 1999. In the beginning, researchers from SCHE studied the artefacts recovered from the lowest rung of the excavation site, which corresponds to the Lower Palaeolithic or the Acheulean period. More recently, they analysed artefacts dug out from the layers on top. So by studying the site layer by layer, scientists have been able to reconstruct the history of human habitation, behaviour and culture in India.

“In the present study, one of our prime objectives was to examine the entire period of Middle Palaeolithic at Attirampakkam with a global perspective – specifically, its origins and evolution,” Pappu said.

To this end, he and his team excavated more than 7,000 stone tools from the sediment layer and analysed them in the lab. They kept an eye out for the presence of telltale marks of tool-making technologies and, based on that, tried to attribute specific uses to these tools. They also examined cores and waste materials that arise from tool-making processes to discern their underlying techniques.

The age of the artefacts was calculated using luminescence dating, which relies on radiation-induced luminescence in natural minerals.

​Exposure to radiation from natural radioactivity introduces minor electronic changes in the structure of minerals like quartz and feldspar. These changes can be uncovered by luminescence. Normally, such changes are reversed when minerals are exposed to sunlight. “So, before burial, the sediments have zero/near zero residual luminescence,” Ashok Kumar Singhvi, a coauthor of the study, explained. “But once the minerals are buried, they start accumulating luminescence due to radiation exposure from its environment.”

Because naturally occurring radioactive minerals decay at a very slow​ rate, the radiation exposure rate remains constant on a million-year time scale. Luminescence analysis of a mineral provides a measure of the “total radiation exposure” it would’ve received since burial – i.e the time when sediments were last exposed to the Sun. Analysing the concentration of natural radionuclides provides the annual rate of radiation exposure. The ratio of the total exposure to annual exposure provides the age.

Singhvi and his colleagues Haresh and Anil from the Physical Research Laboratory, Ahmedabad, conducted a luminescence analysis on sediments surrounding the artefacts. They assumed that the sediments corresponded to the periods when the tools were created. Thus they found that the tools are at least about 172,000 years old – which means they were made 50,000 years before the first Homo sapiens are thought to have reached India, bringing with them their trademark technology.

“These results usher in a paradigm change in terms of how we perceive human evolution and what we know about human dispersal from Africa,” Pappu said.

But the study remains silent on who made these tools.

“Were these technologies brought to Attirampakkam by modern humans or were they developed by other early human species – that can’t be gauged from the data,” Chauhan said. This last piece of the puzzle has multiple implications

A string of evidence from diverse locations has warped the timeline of human dispersal from Africa. Fossils found last year in Jebel Irhoud, Morocco, and a jawbone recovered from a site in Israel suggest that hominins dispersed early, about 180,000 years ago. In fact, according to a rough estimate, modern humans may have ventured out of Africa about 85,000 years earlier than previously thought.

But while conclusions based on data collected from the Moroccan and Israeli sites is held up by fossils, Pappu and her team are yet to recover fossils or DNA that could help them piece together the entire puzzle. Thus, they have been extremely cautious in their study and don’t make any claims about who could have made these tools.

Fossil evidence

“Finding fossils is a matter of luck,” Pappu said. Apart from a single hominin cranium, no fossils from this time-period have been found in India. Given that tools are an important part of human culture and behaviour, she added, “It would be silly to neglect them and focus only on fossils for delineating the history of human evolution.”

But despite the absence of fossils, the scientists are confident that their Tamil Nadu study suggests a succession of population dispersals across South Asia, possibly marked by an interaction between modern humans and other archaic species.

“This is a nice example of using stone tool records to document changes in cultural behaviour,” Mark Stoneking, a geneticist at the Max Planck Institute for Evolutionary Anthropology, Leipzig, told The Wire. “But in the absence of any fossils from the Middle Palaeolithic in India, the conclusions become speculative.”

Even if the Middle Palaeolithic stone tool technology developed much earlier in India and is contemporaneous with similar developments in Africa and Europe, it does not prove that hominins in the Old World interacted with each other at this time.“The tools could have been made by modern humans. They could have also been made by archaic humans,” Stoneking speculated, “so we don’t know if this was an indigenous development in India”; he admits that this “seems unlikely”.

Chauhan, however, holds a slightly different view: “Chances are stronger that the reported Indian technology belongs to archaic hominins,” he told The Wire.

This possibility is supported by the fact that many early humans, including Neanderthals, developed similar technologies without interacting with the Homo sapiens, he said.  “If they can, then archaic humans colonising India could have also developed similar technologies on their own.”

But if we assume that the Early Middle Palaeolithic at Attirampakkam represents Homo sapiens, then there are greater implications.

The artefacts recovered from South India are older than the oldest known Homo sapiens fossils found in Africa (300,000 years ago). Even the oldest fossils outside Africa – recently reported from Israel – are far younger than those found at Attirampakkam.

According to Chauhan, “If the area at Attirampakkam was indeed inhabited by modern humans, it means that the oldest known Homo sapiens fossils have yet to be recovered, wherever their origins may be.”

The study was published in the journal Nature on January 31, 2018.

Sarah Iqbal is a senior research fellow at the department of biochemistry, Aligarh Muslim University, India.