Why do neanderthal genes make COVID worse?

Jonathan - Well, I think Emma should be able to help us with this as well, so maybe you can chip in. But I think to begin with, we have to remember that Homo sapiens and Neanderthals perhaps had a common ancestor between 500,000 and 750,000 years ago. So a long, long time ago, Neanderthal ancestors managed to leave Africa and end up in much of western Eurasia. And I think evidence has been found everywhere from Gibraltar all the way to the Altai mountains in Siberia right?

Emma - Yeah, absolutely.

Jonathan - So from a kind of epidemiological perspective, Neanderthals and Homo sapiens were growing up in, or were evolving in very, very different conditions. So you had Neanderthals evolving to adapt to the challenges posed by a temperate climate. And you had Homo sapiens evolving to adapt to the challenges in tropical areas

Emma - Sub-Saharan Africa. So quite a different environment.

Jonathan - And because biodiversity's much higher in the tropics, you don't just have more vegetation, you have more animals, you have more parasites that live on those animals. So the disease burden carried by Homo sapiens was different.

Chris - They're evolving in different environments, so they're therefore facing and responding to different challenges, which is gonna select for different sorts of genetic endowments, as it were, to resistance to different diseases. So how does that then address the question of the Neanderthal genes changing our risk of Covid?

Jonathan - So let's do another step as well because I think it's really fascinating and builds on what we talked on before, but 15 years ago, we didn't know whether Homo sapiens and Neanderthal had actually met, but after the genome of Neandertals was kind of restructured, we realized that humans have about 2% of Neanderthal dna. And this isn't just random DNA, this is gene variants that help Homo sapiens adapt to the environment that they face when they're migrating out of Africa 40,000 years ago. So quite a few of these gene variants are to do with the immune system and maybe Emma wants to take over

Emma - Yeah, and so actually you're absolutely right. There's these different variants that are associated with different aspects and different functions of our immune system, and it has been shown by one paper that there's a certain variant that we can track back to Neanderthals that increases susceptibility to covid. On the other hand, we've got another variant that actually offers some protection as well. So it's a balance and it's not clear Neanderthal genes are bad or good, so to speak in terms of covid susceptibility.

Chris - It's still extraordinary to think that running around in about 2% of our genomes are genes that would've been carried by this other group of our ancestors dating back more than 50,000 years.