AS BEST AS scientists can tell, Neanderthals died out around 40,000 years ago. But they did not vanish from the Earth entirely. In the past decade it has become clear that Neanderthals mated with the ancestors of modern humans, and that at least some of those unions produced viable offspring. The upshot is that almost half of the Neanderthal genome still survives, scattered in small quantities among almost all modern people's dna. (The exception is those with mostly African ancestors, for Neanderthals seem never to have lived in Africa.) Such genes have been associated with everything from hairiness to fat metabolism. Many seem to be related to the immune system, and to affect the risk of developing diseases including lupus, Crohn's and diabetes. A pair of recent papers suggest covid-19 belongs on that list as well. Two long sections of dna, both inherited from Neanderthals, appear to confer resistance or susceptibility to severe covid-19, depending on which is present.
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