by a Newsnet reporter
Gliog an seo gus an aiste seo leughadh sa Ghàidhlig
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One of the great breakthroughs in modern genetics was the discovery that all modern humans are descended from a small population of African people who migrated out from East Africa around 80,000 years ago and went on to colonise the world. A new study by geneticists reported in the scientifical journal Science Express has found evidence that the earliest modern humans in to arrive in Europe interbred with Neanderthals they found already living here.
On leaving Africa early modern humans discovered groups of people descended from pre-modern human species who had left Africa hundreds of thousands of years previously. In Europe and Western Asia, these pre-modern people evolved into the Neanderthals, a different species of humanity. In Eastern Asia they evolved into a shadowy people known as the Denisovans, after a cave in Siberia where ancient remains were discovered.
The differences between the modern humans from Africa and the Neanderthals and Denisovans were vastly greater than the differences between modern human races, which on a genetic level are trivial and unimportant. With the discovery that Neanderthals were a separate species, many scientists doubted that it was physically possible for modern humans to interbreed with Neanderthals or Denisovans and to produce live fertile young. In the animal kingdom when two closely related species interbreed the result is often infertile offspring such as the mule, the product of interbreeding between the horse and the donkey.
Modern humans and Neanderthals co-existed for a very long time. Although our ancestors left Africa around 80,000 years ago, it was another 30,000 year or more before they began to colonise Europe, until then the homeland of the Neanderthals. Neanderthals finally went extinct around 25,000 years ago. The most recent Neanderthal remains date to 28,000 years ago and were discovered in southern Spain.
Given the sexual proclivities of the human race and the thousands of years in which our ancestors interacted with Neanderthals, it was almost certain that modern humans had sex with the older species, the question was whether the results of these contacts had left any effect in the gene pool of modern people. This new study confirms that a small but significant percentage of modern human genes in non-African populations comes from these pre-modern species. Not only did humans interbreed with Neanderthals and Denisovans, but the children produced by such liaisons were fertile and went on to have children on their own.
Previous research had already established that around 4% of modern human DNA comes from these pre-modern non-African species of humanity. The latest research pins these genes down and identifies them. Parts of the human immune system common outside of Africa appear to derive from Neanderthals and Denisovan people. According to the study, these parts of the system, variants of a gene called HLA, help protect humans from some bacterial infectons and viruses and from the rejection of tissue transplants.
The scientists estimate that Europeans and Asians owe more than half their variants of one class of HLA gene to interbreeding with Neanderthals and Denisovans.
According to Peter Parham of the Stanford University School of Medicine, who was the lead researcher in the study, “The HLA genes that the Neanderthals and Denisovans had, had been adapted to life in Europe and Asia for several hundred thousand years, whereas the recent migrants from Africa wouldn’t have had these genes. So getting these genes by mating would have given an advantage to populations that acquired them.”