An international team of researchers has found that Neanderthals were hit by a major population crisis that began about 75,000 years ago.
Going back a while, almost all of the modern Neanderthals in Europe were like that descendants of one small group.
This low genetic diversity may have contributed to their extinction, around 40,000 years ago.
“We have evidence that Neanderthals lived in Europe periodically between 400,000 and 40,000 years ago,” says paleogeneticist Cosimo Posth, from the University of Tübingen, Germany.
“However, we have only limited information on their population history. So far, we know very little about the evolutionary development that led to their extinction.”
To investigate, the researchers of the new study combined DNA analysis with existing archaeological evidence to explain how, approximately 75,000 years ago, the conditions of the Ice Age may have forced widespread groups of Neanderthals to return to one safe place, or refugium, somewhere in the southwest of France.
The Late Neanderthals of Europe who were studied here lived between 60,000 and 40,000 years ago. The researchers analyzed mitochondrial DNA (or mtDNA), which is passed down through the maternal line, from the bones and teeth of 59 individual Neanderthals.
Although mtDNA does not have a complete genome like normal DNA, it is better able to survive in the environment for tens of thousands of years. It is also easy to extract fossils, as was done here.
Through statistical analysis of mtDNA, the researchers were able to pinpoint 65,000 years ago as the time when the population’s genes began to exchange again – at which time the Neanderthals were able to escape from the Ice Age refugium again.
Although the mtDNA samples were taken across a wide area, the same maternal genetic branch was dominant in all of them, indicating the shared ancestry of a small group of individuals.
“This explains why almost all modern Neanderthals that have been sequenced so far – from the Iberian Peninsula to the Caucasus – have inherited mitochondrial DNA,” says Posth.
However, it was not easy sailing forever. MtDNA also showed a sudden decline and decline in Neanderthal genetic diversity between 45,000 and 42,000 years ago.
This is evidence of a large and rapid decline in population numbers before the final extinction, which is thought to have been about 40,000 years ago.
It is a strong indicator of a species that has been expanding and splitting repeatedly into smaller groups – making it vulnerable to natural disasters, environmental stresses, and genetic pressures (including disease and mutation).
Although several assumptions need to be made to piece together the timeline the researchers have presented here, and mtDNA does not provide the complete picture that DNA records do, the study makes a strong case.
It means that we probably shouldn’t think of the Neanderthal descendants of Europe as linear. Instead, it contracted, expanded again, and collapsed, before completely disappearing – that’s the story told here.
Each new Neanderthal study contributes something to this fascinating period of history, earlier A wise man became the most common species in the world. Learning more about Neanderthals can often lead to a better understanding of our species and our history.
Related: Neanderthals May Never Have Extinct, Study Reveals
The study also shows how different methods of analysis in the same study – in this case both mtDNA and a wide collection of archaeological records, showing the movements of Neanderthals in time – can be used to reconstruct ancient history in a meaningful way.
“This allowed us to combine two pieces of evidence and reconstruct the population history of Neanderthals in terms of space and time,” says Jesper Borre Pedersen, a paleolithic archaeologist at the University of Tübingen.
Research published in PNAS.
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