How Neanderthal DNA affects human health -- including the risk of getting Covid-19

This file photo shows a reconstructed Neanderthal skeleton (right) and a modern human version of a skeleton (left) on display at the American Museum of Natural History in New York.

(CNN)Early modern humans originated in Africa and started spreading around the world about 80,000 years ago. As they traveled, they came across other ancient humans, including Neanderthals, who had already populated Europe and parts of Asia. Some of them had sex and gave birth to children -- current-day human DNA still carries echoes of these prehistoric sexual encounters.

The evidence that Homo sapiens interbred with Neanderthals first emerged in 2010, after Swedish geneticist Svante Pääbo pioneered methods to extract, sequence and analyze ancient DNA from Neanderthal bones. Pääbo mapped the entire Neanderthal genome, and thanks to his work, scientists can compare Neanderthal genomes with the genetic records of living humans today.
Most living people can trace a very small percentage of their DNA to Neanderthals -- and that likely includes Africans, who until recent