Science & Environment

'Health risk' legacy from Neanderthals

illlustration of Neanderthal family Image copyright Science Photo Library
Image caption Significant traces of Neanderthal ancestry are found in modern human DNA

Some instances of depression, among other ailments, may be influenced by our Neanderthal heritage.

Scientists say a range of conditions, including skin disease and even a tendency towards tobacco addiction, have strong links to the DNA we retain from our ancient evolutionary cousins.

A US-led team found the associations when searching for Neanderthal genetic variations in 28,000 modern-day people.

The study appears in Science magazine and is the largest of its kind so far.

"I want to stress that none of this is directly causal," said senior author Dr Tony Capra from Vanderbilt University in Nashville, Tennessee.

"The associated diseases we've identified are complex, and will have a large number of genetic and environmental factors. And in many cases the Neanderthal contribution will be significant but it's not like you are doomed to be a life-long smoker just because you have that bit of Neanderthal DNA," he told BBC News.

Blood clots

It is recognised now that our direct forebears interbred with Neanderthals about 50,000 years ago, when we entered Eurasia from Africa.

This interaction has left its mark on many people of European origin today: their genomes contain anywhere between 1% and 4% Neanderthal DNA.

The revelation stems from recent work to read the entire genetic blueprint of Neanderthals - made possible by examining their fossil remains.

Dr Capra and colleagues trawled this ancient "life code" for small, tell-tale "spelling mistakes" - what are called single nucleotide polymorphisms, or SNPs. And then, with access to a huge database of anonymised hospital medical records, they went looking for those same signature variations in the DNA of nearly 30,000 people.

The team identified 135,000 SNPs in modern-day patients that very likely came from Neanderthals.

"Once you've got that information, you can start to test whether there is an influence on risk for disease," Dr Capra explained.

Strong correlations were found for 12 traits, including an increased tendency towards immune issues, heart attack, and blood disorders.

One of these associations concerns hypercoagulability. In ancient times, it might have been quite useful for blood to clot more quickly: a wound would close faster and an infection would find it harder to set in.

But in the modern setting, where people no longer have to hunt dangerous wild animals, the trait is definitely less advantageous. Hypercoagulation can increase the risk for stroke, embolism and complications in pregnancy.

Image copyright Science Photo Library
Image caption Clotting blood: more useful 50,000 years ago

What is striking, says Tony Capra, is the number of associations that seem to have their origin in environmental interactions.

"As our ancestors moved out of Africa into the Middle East, Asia and Europe, they would have entered very different environments than back in Africa - different in terms of climate, of diet and importantly in terms of the pathogens they encountered.

"Neanderthals had been living in these new environments for hundreds of thousands of years before we got there, and they were better adapted to those unique environments. So the hypothesis is that by breeding with Neanderthals, we got some of those adaptive benefits without having to evolve them ourselves."

Dr Capra hopes the study of Neanderthal genetics will open new routes to understand disease, its causes and how to treat it.

The Vanderbilt researcher presented his work here in Washington DC at the annual meeting of the American Association for the Advancement of Science, the publishers of Science magazine.

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

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