WhyallaI’m in Whyalla and I’m thinking about Neandertals. There’s a joke there somewhere if you’re a South Australian, but it isn’t actually a very fair one, or a very good one for that matter. So far, my day in Whyalla has been chock full of bright friendly people and even good food. That being said, I’m at my university’s regional campus rather than One Steel’s blast furnace.

Actually, it’s probably a bit unfair to make Neandertal jokes about Neandertals. Most people who study these sorts of things think that Neandertals were probably pretty decent folks. They used tools, “they took care of individuals that would not have been able to provide for themselves, there are burials so we know that they cared for the dead, there is evidence for symbolic behavior, and it is clear that they were intelligent.” Maybe even more civilised than our human ancestors who very possibly killed them and ate their Neandertal cousins and may have wiped them off the face of the planet entirely.

You may have already worked out that I’m a bit of a human origins anorak. This is my fourth post about Neandertals, meaning that the only topics I’ve spent more time on in this blog is my kids. And the Georgia Bulldogs.

Some of you may have seen the news stories about the sequencing of the Neandertal genome a couple of weeks ago. I intended to sort of leave it alone. “Self, it’s just another sequenced genome”, I said to myself. But it turns out that this one, in the words of the American vice-president, is a big fucking deal*.

neanderthal-615It isn’t just the sequencing of the genome, a massive technological accomplishment in its own right. A gaggle of researchers from around the world managed to obtain the sequence of the Neandertal genome from a handful of bones found in a cave in Croatia. Modern humans and Neandertals are genetically very similar. The biggest problem that researchers face when trying to sequence the Neandertal genome is DNA contamination from human scientists. Any of you who have watched a single episode of the myriad CSI’s and their clones on TV know that we shed DNA all over the place in the course of a day. The researchers go through great pains to minimise this contamination and also get rid of random microbial DNA that builds up on bones that have been lying around in caves for 40,000 years or so. The result of all this work is the first published report of Neandertal sequence that is really convincing.

What makes this a bigger deal, however, is a couple of things that the researchers managed to work out by comparing the Neandertal sequence to modern humans and our closest extant relative, the chimpanzee.  First, they’ve found some particular parts of the genome that are unique to modern humans. These parts of the genome are of interest because they may represent regions that have undergone positive selection. We all (hopefully) know that the driving force of evolution is natural selection. Well, selection can be negative (weeding out an undesirable trait), neutral or positive. The latter occurs when a particular trait is so beneficial to the organism and thus becomes dominant to other traits until it becomes fixed – or present in all of the population.

328_710_F6Well, the Neandertal researchers found a handful of genes in which a particular variant appears to have become fixed in modern humans that wasn’t present in Neandertals. Some of these are in genes that are expressed in the skin, which seems to imply that there is something special about modern humans’ skin morphology or physiology that gave us a selective advantage over our ill-fated Neandertal cousins. Other genes that exhibit evidence of positive selection in humans are ones involved in cognitive and skeletal development, though these are rather unsurprising.

But the real BFD finding for me is the evidence presented that our modern human forebears and Neandertals, well, got it on. I teach this stuff in my genetics course. And every year I present data that ‘proves’ there was no viable interbreeding between the two species. All the genetic evidence generated to date supported that if humans and Neandertals got a bit frisky on a cold winter night in the cave that they didn’t produce any kids that are related to you or I.  The current paper compares the Neandertal genome to present-day humans from sub-Saharan Africa, Papua New Guinea, China and France. What they found absolutely floored me. They showed that Neandertals share more genetic variants with the individuals from China, Papua New Guinea and France than with the Africans. What this means, unequivocally, is that Neandertals and anatomically modern humans mated and produced viable offspring. They did so before modern humans began to spread northwest into Europe and east into Asia and the Pacific but after they migrated out of East Africa. And it wasn’t just a one night stand – between 1-4% of the Eurasian genome is derived from Neandertals.

The implications of this are not entirely clear. If you’re of European or Asian ancestry are you part Neandertal? Almost definitely. Does it matter? Did these Neandertal sequences that have been retained in the modern human genome give Eurasians a selective advantage as they spread around most of the rest of the world? Well, that’s harder to say. But most analyses I’ve read suggest that the Neandertal sequences are neutral, just a relic of a little interspecies loving ‘surfing’ the DNA wave. But I’m not sure. I think that we don’t have all the information that we need to make conclusions about the evolutionary significance, or lack thereof, of this Pleistocene interspecific shagfest.

I guess what it does mean that there are Neandertal descendents roaming around Whyalla after all.

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* Actually, in the grand scheme of things, this is probably a bigger fucking deal than a half-assed health care compromise that isn’t likely to do much of anything to solve the morass that is the American health care system.

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Image credits:

Whyalla

Neanderthal woman

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