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How Neanderthal DNA affects our immunity

Science Correspondent Lydia Beckett investigates how Neanderthal genetics influence modern immunity to diseases such as Covid-19.

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You may have heard the statistic before that Europeans and Asians have about 1 to 4 percent Neanderthal DNA. But what does this mean in reality and how have these genes actually affected our characteristics and our lives today?

A recent paper by Zeberg and Pääbo in 2020 discovered a particularly pertinent link to our neanderthal ancestry in the current social climate; a major genetic risk factor for severe Covid-19 is inherited from Neanderthals. In order to come to this conclusion, the authors compared genetic code with a pre-established link to Covid-19 and the same areas of DNA of sequenced Neanderthal genomes from southern Siberia and Croatia. The study found these Neanderthal genomes also had these genetic variants associated with severe Covid.

This gene is present in around 50 percent of south Asians, and 15 percent of Europeans, leading to an overly aggressive, potentially fatal immune response that increases the risk of respiratory failure. According to the office for national statistics, during the pandemic the rate of death involving Covid-19 in the UK was higher for ethnic minority groups, particularly for individuals of Bangladeshi origin, and in some cases was used as ammunition for prejudiced narratives, however this research demonstrates that a large component of this is probably genetic disposition since more than half the population of Bangladesh (63 percent) are carriers for the gene. This exhibits the power of archaeological genomics as not only an interesting tool to learn about the past, but also as a map that tells us how and why we got to where we are now as well as all the bits in between.

Since evolution is the result of disadvantageous genes killing individuals before the chance to reproduce, the authors hypothesised why such a lethal gene would have been conserved over the past tens of thousands of years. It does seem counterproductive. At this point, there is only speculation, but one possibility is that it provided protection against other pathogens. Another question is what this means for Neanderthals, and how it may have affected their immune systems. But since it is not known how this gene functions in conferring the risk for severe Covid, and whether the effects are specific to SARS-CoV-2 or also possibly to other corona viruses or pathogens, it is hard to untie the genetic knot of what this means for Neanderthals currently.

So why is this gene more prevalent in some populations than others? Neanderthals evolved from a branch of an archaic human species known as Homo heidelbergensis (our common ancestor with Neanderthals) that migrated into Europe during the middle Pleistocene. Neanderthals occupied southern and parts of northern Europe, the middle east, and extended into parts of Asia. Then, when homo sapiens started to migrate into Europe around 40,000 years ago and they came in contact with the genetically distinct Neanderthals, there was some interbreeding between them. This is why African populations have little to no Neanderthal ancestry since the interbreeding occurred after both sub-species had migrated out of Africa. For the rest of the world, Homo sapiens carried the neanderthal ancestry with them as they migrated down into Australasia, and also across the Bering strait into America. However, the authors noticed there were some inconsistencies. For example, the extent of difference in allele frequencies for the gene between south and east Asia are dramatic and unusual considering the proximities (east Asians having much less instances of the gene). They speculate this could be due to negative selection, perhaps due to similar coronaviruses or other pathogens at some point in that area. But some regional variation may be to do with genetic drift (population wide fluctuations in gene variants caused by no selection pressures but instead by chance).

Interestingly, there are also many other investigated Neanderthal genetic factors on modern communities. For example, there has been research that links Neanderthal genetics with increased pain sensitivity, propensity to depression, nicotine addiction and sleep patterns. Links have also been made with another archaic hominid species, the Denisovans, who also interbred with both Neanderthals and Homo sapiens. One Denisovan gene has given some modern Tibetans a ‘superpower’ that allows them to survive at high altitudes.

As we understand more about the way past species have shaped who we are today, we learn more about how our genetics influences our lives, which could be an important tool for healthcare and psychology. For example, perhaps Neanderthals can help us learn more about genetic disposition to depression and addiction and how it could be treated more effectively. Despite being technically extinct for 40,000 years, the legacy of the Neanderthals lives on within many of us, to our detriment and to our benefit. Or perhaps they are not truly gone, look in the mirror… what do you see?

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