New Research Tracks Neanderthal Traits in Modern Humans

New studies strengthen the evidence that Neanderthals have a genetic impact on everything from bad habits to good cholesterol in people today.

Hidden in a cave in northern Croatia, a fragment of bone from a woman that lived 52,000 years has revealed its secrets, suggesting that we’re even closer to our evolutionary ancestors than we thought.

This is only the second time that we’ve sequenced the genome of a Neanderthal to such a high level of detail, says Kay Prüfer at the Max Planck Institute for Evolutionary Anthropology in Germany. Thanks to this analysis of the ancient fragment, we now know that for modern humans outside of Africa, as much as 2.6 per cent of our genome is made up of Neanderthal DNA.

This suggests that Neanderthals may have mated with our own species – Homo Sapiens – as early as 130,000 years ago. This genetic mixing left a handful of genes that are still active in most humans today – including those that influence our blood cholesterol and vitamin D levels, our fat accumulation and how we respond to antipsychotic drugs. Other genes the researchers identified included those connected with rheumatoid arthritis, schizophrenia and eating disorders.

This new study highlights how little really separates us from our extinct cousins, says Simon Underdown at Oxford Brookes University in the UK. It could have just as easily been us that ended up going extinct around 40,000 years ago, he says. “I think that it might have been bad luck – we could be having this conversation as Neanderthals and thinking about how lucky those Homo sapiens were to get wiped out.”

This latest analysis sheds a little more light on why the Neanderthals went extinct in the first place. We’re still not quite sure what caused their demise – but Prüfer’s study estimates that Neanderthals tended to live in populations of around 3,000 individuals.

This might sound like a decent population size, but from a genetic point of view it barely provides enough diversity to stop genetic defects from accumulating. “A population of 3,000 is only just safe,” says Chris Hunt at Liverpool John Moores University. “It shows how marginal the Neanderthals were as a breeding population.”

It was previously thought that, given these limited population sizes, inbreeding may have been common among Neanderthals. Last year a genomic sequencing of a Neanderthal toe bone found in south Siberia suggested that the individual’s parents were half-siblings. “This is genetically very dodgy,” Hunt says, and a sign that a species doesn’t have an adequate population size.

These small, spread out, clusters of Neanderthals may partly explain their extinction, says Underdown. “Because it’s such a small population it doesn’t take much to wipe them out.” A cave in might have wiped out one group, while another may have been out-competed in a certain territory. Over tens of thousands of years these tiny wipe outs may have contributed to the gradual extinction of the species.

For Hunt, studying Neanderthals helps us understand a little more about our own existence. “When you look at what they are capable of, it’s not much different to what we were capable of at the same time.”

But unlike us, the Neanderthals never went on to dominate – or set about destroying – the entire planet. For most of their existence, they lived a marginal existence. Just about surviving for hundreds of thousands of years. “They were isolated from humanity – in the broadest sense – and they just about managed,” Hunt says.

Yet this new study suggests that early modern humans and Neanderthals came into contact and may have lived alongside each other. “It’s showing that there are relationships between them and us,” Hunt says. The genetic trace of those relationships remains in most of us today. “In a sense, they are us.”

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