Some COVID risk genes come from Neanderthals
A cluster of genes that is linked to more severe cases of COVID-19 appears to have originally come to us from Neanderthals, according to a report in Nature. Chris Smith asked Sean Carroll, Theo Bloom, and Lee Berger to unpack the story...
Lee - So Neanderthals are both a lot like us, and a lot different from us. They're more robustly built, they're shorter, they're stockier; and they were considered an absolutely separate species. In fact, scientists used to get in bone fights over whether or not we wouldn't run away from each other, and they'd ever even met. And then ancient DNA came along, and that plays into this story because we mapped out the Neanderthal genome, and suddenly we found out that most humans - including many Africans - had some levels of Neanderthal DNA, something between 1% and 5% within us. And that's where this story comes in.
Chris - And Sean, would you judge that in the book as a fortunate event - the interbreeding of us with Neanderthals - or not? When it comes to coronavirus, it sounds like it might not be...
Sean - Might not be. No one can tell the future; and so really natural selection only operates in the present. So probably the reason why this block of DNA is in a significant number of humans is that there was some positive selection for it, but now here's this new pathogen and it's a disadvantage. And that's a very common story about human genetics. We know, for example, that there's a very rare variant that makes people impervious to HIV. The HIV virus is perhaps a century old, but this variant we can find in bronze age bodies buried in Europe. So these genetic variants have been around for a long time, and perhaps they were favoured by certain other pathogens; they may have conveyed resistance to other pathogens, but now they're either advantageous or disadvantageous to new ones that come along now.
Chris - Theo, what's your reading of Sean's fortunate events? He made reference to our parents gonads, and he's getting at basically the rearrangements of genes in there that render us unique on Earth - unless we have a twin or we've cloned ourselves.
Theo - Yeah. So this notion that, although we're initially taught that genes all behave independently, actually they're inherited in blocks along chromosomes that are inherited together simply by proximity. And this example of the piece of Neanderthal DNA that seems to have an effect on COVID resistance: who knows what genes it may carry, or why it was selected for at some point during evolution. At this point we don't know; we just know that there's a linked box of DNA that's come to us from our Neanderthal ancestors, and it seems to be differently distributed among different groups on Earth at the moment, and may even underlie some of the differences in susceptibility to COVID. But really we're very early in understanding that story, I would say.
Chris - Do we have any idea why those Neanderthals had those genes, and what they did for them?
Sean - The first answer to that is a flat out no, we have no idea. And the second answer to that is a lot more complex. No, they didn't have to have an advantage. They might've just been there and we might just carry them. We need to be cautious about direct attribution, particularly in the middle of a pandemic, because as Theo would absolutely know - I'm sure you were inundated with these ideas - we don't know this right now. It will have to prove the test of time. Don't think that if you carry Neanderthal DNA that you're at some higher risk of this, or if you don't, you're at lesser risk; keep wearing your mask, keep social distancing. Those are the things that work until we get a vaccine.
Chris - And Sean Carroll, the author of A Series of Fortunate Events, I suppose it was another fortunate event that you were able to come on our program today! So thank you for joining us and thanks for telling us about the book. What do you think the next most fortunate event is going to be? A vaccine?
Sean - Yeah, well, that's not fortunate. That's just science, and scientists working very hard. And I have a little inside insight to that through a documentary film that we're making; and there are people whose names you don't know who've been working tirelessly around the clock, in an unprecedented challenge to develop this vaccine. So I think that's a nice side effect of our big brains, is the practice of biomedical science. So hopefully that'll get us all in person in 2021.