Homo sapiens migrated to the continent in waves – but the reasons for their early failures to overcome Neanderthals are a mystery
Sun 14 Nov 2021 03.30 EST
Modern humans made several failed attempts to settle in Europe before eventually taking over the continent. This is the stark conclusion of scientists who have been studying the course of Homo sapiens’s exodus from Africa tens of thousands of years ago.
Researchers have recently pinpointed sites in Bulgaria, Romania and the Czech Republic where our ancestors’ remains have been dated as being between 40,000 to 50,000 years old. However, bone analyses have produced genetic profiles that have no match among modern Europeans.
“These early settlements appear to have been created by groups of early modern humans who did not survive to pass on their genes,” said Professor Chris Stringer of the Natural History Museum, London. “They are our species’ lost lineages.
“The crucial point is that the demise of these early modern human settlers meant Neanderthals still occupied Europe for a further few thousand years before Homo sapiens eventually took over the continent.”
Modern humans first appeared in Africa around 200,000 years ago and slowly evolved across the continent before moving into western Asia around 60,000 years ago. Our ancestors then spread across the globe until every other species of hominin on the planet had been rendered extinct, including the Denisovans of east Asia and Homo floresiensis, the “hobbit folk” of Indonesia.
Neanderthals in Europe were one of the last hominin species to succumb, dying out around 39,000 years ago. However, recent studies – outlined at a meeting of the European Society for the study of Human Evolution earlier this year – have shown that this takeover by Homo sapiens was not straightforward. On several occasions, groups of early settlers perished as they moved into the continent.
In one study, international researchers re-examined a partial skull and skeleton of a woman found in the Zlatý Kůň cave in the Czech Republic. Originally thought to have been 15,000 years old, this new analysis indicated it was probably at least 45,000 years old, making her one of the oldest members of Homo sapiens found in Europe. However, the study also found she shared no genetic continuity with modern Europeans.
As one of the research team – Cosimo Posth, of the Institute for Archaeological Sciences, Tübingen University, Germany – put it: “This woman did not contribute genetically to present-day Europeans.”
Other sites where early modern human remains from around this period have been found include Peștera cu Oase in Romania and Bacho Kiro cave in Bulgaria. And again, neither has produced genetic profiles that left a significant trace in Europe.
The discovery of these lost outposts of modern human expansion suggests that Homo sapiens dispersed into Europe in pulses, and raises critical questions for scientists. In particular, why did modern humans’ later forays into Europe succeed when earlier ones failed? The impact of this success on our world has been significant, after all. Some scientists argue that environmental factors played a key role in the Neanderthals’ demise. Possible triggers include the reversal in Earth’s magnetic poles that occurred around 42,000 years ago. Known as the Laschamps event, it could have increased cosmic radiation levels across the planet for several centuries.
There was also a cooling of the climate that affected the North Atlantic at this time, as well as a major volcanic eruption of the Campanian ignimbrite caldera in central Italy. All of these would have put stress on populations.
But some researchers question whether these events were damaging enough to lead to Neanderthal extinction. They would have been just as challenging to modern humans, they argue, yet we survived.
Others have proposed that Homo sapiens were simply better at exploiting the landscape and hunted more effectively, a point backed by Stringer, who argues that minor changes in human behaviour at this time could have been enough to lead to the accumulation of significant improvements in the lives of men and women.
“The behaviour of Homo sapiens was a big factor in our ‘success’, I think. Maybe we networked better, or accumulated knowledge more effectively, and so learned how to extract resources more intensively than Neanderthals did. Any slight advantage would have been critical. You’ve only got to increase survival of your babies by 1% and that is a huge advantage in a stone-age world.”
However, there is another factor that has been put forward for modern humanity’s success in Europe. Genetic studies have made it clear that interbreeding between Homo sapiens and Neanderthals occurred many times. As a result, men and women of non-African origin today have genomes that are around 2% Neanderthal. That figure would have been much higher 40,000 years ago.
“As numbers of Homo sapiens grew and we spread ever wider across Europe, it is quite possible that we ‘absorbed’ some of the other species – in particular, the Neanderthals – out of existence,” said Stringer. “If prime-age Neanderthals were entering the modern human breeding pool, whether voluntarily or otherwise, those individuals were no longer contributing to the survival of their own species. The end result would have been straightforward extinction for the Neanderthals – although, as a species, they still survive in the DNA of men and women today.”