Genetic studies and stones tools from are calling into question the longstanding belief that modern humans colonised Eurasia from Africa 60,000 years ago.
The evolutionary origins of modern humans and the mapping of ancient hominin migrations across the planet are currently in a growing state of flux. A spate of new physical discoveries and improved genomic models are helping scientists to rewrite the human story.
The understanding we have of our distant prehistoric ancestors comes mainly from a limited and fragmentary collection of finds. This dearth of data has always made it difficult to pin down the definitive narrative of our early origins. One pivotal moment in the development of our species that has been considered well understood for the last three decades is the expansion of modern human populations into Europe and Asia around 60,000 years ago. The popular understanding was that this event involved a migration beginning in sub-Saharan Africa that was likely driven by salubrious climate and so-called green corridors of natural resources leading these migrants beyond the continent.
While it is undoubtedly true that the ‘Recent Out of Africa Theory’ remains extremely widely accepted among academic scholars, it is no longer founded on stable ground. A series of discoveries are threatening to consign this theory to the past. Perhaps most surprising part of this change is the fact that the contradictory evidence is emerging from studies focused on the mostly side-lined (from a palaeoanthropology perspective) continent of Australasia.
The scientific community has for many years posited that the first humans to reach the Australasian landmass had walked from East Africa to Southeast Asia by around 55,000 years ago. Encountering the Indonesian Ocean these bands of wandering explorers engineered the world’s first boats with which they then sailed through the islands of Indonesia, perhaps settling some of these as they moved, before reaching the shores of the Australasian continent’s 50,000 years ago. This scenario meshed well with the expectations of the recent out of Africa model and embraced most of the available evidence.
Then in July 2017, there came the announcement of 65,000-year-old stone artefacts from an Aboriginal rock shelter site at Madjedbebe in the Northern Australia’s Kakadu National Park. The resulting paper “Human Occupation of Northern Australia by 65,000 years ago,” was published in the eminent scientific journal, Nature. Included in its pages was a discussion of associated stone implements that produced potential age dates close to 80,000 years. Due to the conservative nature of the archaeological study, the more recent minimum datings were favoured.
“People got here much earlier than we thought, which means, of course, they must also have left Africa much earlier to have travelled on their long journey through Asia and south-east Asia to Australia.” – Professor Chris Clarkson, University of Queensland (lead author).
The tools are of a type previously only known to have been used by modern humans and yet there is no conceivable way in which the presence of modern humans in Australia 65,000 years ago can mesh with a migration leaving Africa 60,000 years ago and moving slowly through Eurasia towards Australia. Even if the migration model is revised to 73,000-years ago, which for several reasons is considered to be the absolute upper-limit before the model collapses completely, it still fails to make sense of the findings.
Most academics agree that 8000 years is far too quick for the journey in hand, what would drive a small population of migrants (as indicated by the genetic data) to range so incredibly far at such speeds. These people hurriedly passed through bountiful landscapes without settling. Instead of reaching the welcoming coastlines of Southeast Asia and then settling down to some fishing, they instead set to the job of engineering a novel method for crossing the dangerous seas ahead. The journey would necessitate crossing the Wallace Line, a natural barrier which separates flora and fauna of Asia from that of Oceania and involves incredibly strong south-westerly ocean currents. All this to reach a continent that these migrants couldn’t have known existed.
There is, however, a significant problem for scientists that might try to adjust the start date of the migration into Eurasia. Multiple genome studies have indicated that the ancestors of modern Eurasians diverged from their source population, assumed to be Africans, between 60,000 and 50,000 years ago (with a strong preference for 55,000). This fact is extremely inconvenient for anyone that wants to simply keep pushing back the beginning of the story, the genetic data is very clearly indicated that the population divergence resulting from the exodus happened no earlier than 60,000 years ago.
You might well be wondering why anthropologists are so convinced that the human expansion began in Africa and not some other part of the world. Let’s quickly recap how we got to the current popular understanding.
It’s all to do with modern African genes. The ancestors of all living European and Asian populations carried the mitochondrial haplogroups M and N (maternal line genetic markers). These people also had Y-chromosomal haplogroup CF (paternal line genetic markers). Analysis of modern African DNA revealed that these Eurasian haplogroups were very closely related to a mitochondrial Haplogroup named L3 which had appeared in these genomes around 70,000 years ago. It was then assumed that this haplogroup had emerged as a mutation occurring within a population resident in Africa at that crucial time.
It is essential to highlight the fact that there were no ancient DNA samples from any African fossils involved in the studies. Today we still have no genetic material from African human fossils older than 15,000 years. In simple terms, there is no direct DNA evidence at all, which can be used to support the claim that HgL3 emerged in an African population 70,000 years ago.
Unknown to the general public there has been several academic papers which suggested perhaps the source population for HgL3, and thus for Eurasians, was already living somewhere in Western or Southern Asia. Now a more recent study has again questioned the assumptions in the recent out of Africa theory.
Researchers at the University of La Laguna have suggested that haplogroup L3 entered Africa during a migration event, explained in a paper titled “Carriers of Mitochondrial DNA macrohaplogroup L3 Basic Lineages Migrated Back to Africa from Asia Around 70,000 Years Ago.” Though the authors of this paper still suspect there might be a possible earlier African origin for these migrants, they highlight an extraordinary, glaring, anomaly within their accrued data:
“The southern route hypothesis proposes that the Eurasian branches (M and N) of the macrohaplogroup L3 differentiated in or near the African continent and rapidly spread across the Asian peninsulas to reach Australia and Melanesia. Under this assumption, it is expected that, in general, coalescence ages of haplogroups should decrease from Africa to Australia. However, we have demonstrated that this is not the case. Just on the contrary, the oldest M and N haplogroups are detected in southern China and Australasia instead of India, and associations between longitudinal geographic distances and relative ages of M and N haplogroups run, against to expectation, westwards with younger haplogroup ages going to Africa.”
With confirmation that people were living in Australasia 65,000 years and using tools only known to be associated with modern humans comes a headache for the anthropological community. Knowing that Aboriginal Australians, not Africans, carried the oldest variants of the haplogroups considered ancestral for all modern Eurasians, confirms an immediate need to redraw the migration map.
The mounting evidence supports the fundamental understanding of a migration underway from around 60,000 years ago but reverses the direction. It now seems clear we need to look to Oceania and East Asia for the start of the population expansion which swept westwards across Eurasia. This mass movement of people eventually reached Europe and North Africa 45,000 years ago.
This new model resolves the anomalous mystery of why it took 20,000 years for modern humans to walk the short distance from North Africa to Europe, yet reached Australia at lightning speed, it didn’t happen this way at all. The principle of Occam’s razor informs the scientific process, advising us to always select the explanation which involves the fewest speculative leaps. A recent out of Australasia and/or Southeast Asia resolves all the existing anomalies in the story of the populating of Eurasia.