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Trending Science: Modern allergies may be the result of Human-Neanderthal interbreeding

According to two studies in the American Journal of Human Genetics, interbreeding between ancient humans and Neanderthals over 40 000 years ago may have left modern humans more prone to allergies. The studies also highlight how three particular genes inherited from the Neanderthals are vital for the human immune response.
Trending Science: Modern allergies may be the result of Human-Neanderthal interbreeding
Earlier studies have shown that 1-6 % of modern Eurasian genomes were inherited from both the Neanderthals and the Denisovians, a related species that lived in Siberia. The two new studies show that the three particular genes in question (the TLR6-TLR1-TLR10 cluster), essential for the body’s immune response, are thought to have spread to modern humans when small groups of them left Africa to Eurasia and bred with both the Neanderthals and Denisovians.

The Neanderthals and Denisovians had already spent 200 000 years adapting to life in Eurasia, and had developed immune systems that could effectively combat local pathogens, an evolutionary advantage that the modern humans from Africa lacked but then subsequently acquired.

But humans today who have inherited the genes are also more susceptible to an overly-sensitive immune system and are consequently more likely to have asthma, hay fever and other allergies.

By studying modern human DNA collected by the 1 000 Genomes Project, a team from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, found these three genes still play an active role in human ‘innate immunity.’

The team looked at how common the three genes were in people from across the globe. Out of the three genes, two closely matched Neanderthal DNA, with the most common found in all non-African humans, whilst the second only appeared in the genetic structure of Asians. The third gene, being much rarer, and similar to Denisovian DNA, was found only in a small number of Asian participants.

‘A small group of modern humans leaving Africa would not carry much genetic variation,’ said Dr Janet Kelso, who led the research. ‘You can adapt through mutations, but if you interbreed with the local population who are already there, you can get some of these adaptations for free.’

Dr Kelso’s findings have been substantiated in the second published study, where scientists at the Pasteur Institute in Paris, led by Dr Lluis Quintana-Murci, found that the same three genes are prevalent in modern humans when also comparing DNA from the 1 000 Genomes Project to ancient human genomes.

Although the genetic legacy from the Neanderthals and Denisovians appears to be a more robust immune response, there is a trade-off with regards to the increased risk of allergic reactions, as Dr Kelso explains: ‘You have an increased reactivity to potential pathogens, but you also have, as a kind of consequence to that, an increased reactivity to things that are not pathogenic, things like pollen and pet hair.’

Source: Based on media reports

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