(Picture from here.)
I've had a love affair with Neanderthals since I was a kid.
From Brian Aldiss' Neanderthal Planet to Neanderthal references in Sover and Harrison's Apeman, Spaceman, I've been a junkie pretty much forever.
It's not an accident my first short story sale (A Capella Blues) was about the end of Neanderthals. I revisited them last year with a story, Two Boys, about Neanderthal resurrection.
For a long time it's been the position that Neanderthals and Homo sapiens never interbred. This has been, I think, resoundingly disproved by analysis of the recently sequenced Neanderthal genome.
Neanderthals co-existed with European humans for thousands of years. For a species (ourselves) that's been known to copulate with goats and dogs, I've always thought that it was impossible for humans not to have copulated with Neanderthals. I speculated on this in A Capella Blues, thinking that one significant difference between Neanderthals and Homo sapiens was the open ended sexual nature of humans as opposed to a closed estrous cycle of other primates.
The delirious humping mentality of Homo sapiens aside, the question of offspring was always curious. Hence, the research.
The Neanderthal sequences were first reported back in 2006. (Incidentally, inspiring Two Boys.) The work had to be redone because of Homo sapiens contamination. That work was completed and reported in this week's Science magazine gave evidence of interbreeding in several ways.
First, it was noted that the Neanderthal genome was pretty uniformly distinct across much of its range as evidenced by the difference between the samples sequenced and known human sequences. Even so, Neanderthal genetic difference from human appears to be pretty minor. There were only 78 differences in the sequences that "encode proteins that are uniformly present in humans but absent in Neanderthals." (See here.)
The similarity between the species is more than skin deep, much of it in the regulation of other genes. Neanderthals had the human form of many regulatory genes 90% of the time. There were still several changes in the Human Accelerated Regions (HARs) that humans had picked up since the original divergence from Neanderthals.
So far, this does not constitute evidence of interbreeding.
The authors looked for what is called a "selective sweep": a mutation that proves useful and migrates through the population since its selective advantageous.
They found 200, many involving neural development. One of which shows evidence of sweeping through humans after we picket up the Neanderthal copy. We've got the Neanderthal copy of the gene.
To push this further, the copy of the gene that is Neanderthal isn't uniformly spread through the human population. It shows up in European and Asian populations much more uniformly than it shows up in African populations. Neanderthals were restricted to Europe and Asia when the human invasion began.
This brings up very interesting ideas. For example, if the genes involved were advantageous enough to spread through one population (Europe and Asia) but not through another (African), what does that mean in modern times? Were they advantageous only in the areas where the Neanderthal was prevalent? Are they advantageous or disadvantageous today? The nature of the sweep says the genes were important enough to sweep through the populations at the time but that says nothing of the nature of the advantage.
Not all the Neanderthal DNA was sequenced: there's not a complete genome available. So we're not going to see my characters from Two Boys any time soon.
But we might some day.
Links:
Original Science Articles
Nobel Intent
Science News: Here, here, here, here.
BBC
Gordon's Notes
John Hawks
Jerry Coyne and here
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