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A little dark hypothesis: I've seen some (intertwined) hypotheses in the news lately of why there's no neanderthal Y chromosomes: the mixed-race-neanderthal-Y
by thedevil 11y ago
A little dark hypothesis:
I've seen some (intertwined) hypotheses in the news lately of why there's no neanderthal Y chromosomes: the mixed-race-neanderthal-Y boys didn't do so well for some reason, the human Y chromosome had advantages, or the neanderthal-Y wasn't compatible genetically.
How about the more obvious guess: homo sapiens invaded and conquered neanderthals, killing all the males (and their Y chromosomes with them). It's speculative, but it would definitely not be the first time in history that such a thing has happened. And the neaderthals live for hundreds of thousands of years, then disappear just tens of thousands of years after homo sapiens show up in their neighborhood. So it's likely one group wiped out the other. And it's not hard to imagine keeping the women when you decide to kill a whole neighboring tribe.
I actually came up with the hypothesis about how the two groups most likely interbred just a few days before I found out in the news that the neanderthal Y-chromosome disappeared. I don't know if I should be excited or disgusted that the evidence might support my hypothesis.
- danieltillett 11y agoHuman history is unfortunately littered with stories like this, but we know the Neanderthal genetic flow came in from the males. The reason why we know this is we are missing all Neanderthal mitochondrial DNA sequences which are only inherited down the female line. If your theory was correct then we would see modern humans with Neanderthal mitochondrial genomes. It appears what happened is much more interesting - Neanderthal males mated with female humans of African origin, but the male offspring were infertile.
- thedevil 11y agoThank you for the insight. I wonder, how do we know the males were infertile?
- danieltillett 11y agoWe don't - all we know is that the Neanderthal Y chromosome is missing from the modern human population. This could have occurred by chance (genetic drift), lethal genetic incompatibility (all males died), or infertility. Given the data we have it is hard to know which of these is the real cause.
- thedevil 11y agoIs it not equally likely the other way around - that the Neanderthal mitochondria disappeared because of unsuccessful mixed females or other genetic drift?
- klipt 11y agoYeah, given the symmetrical evidence: no Neanderthal Y chromosome DNA, and no Neanderthal mitochondrial DNA - it seems most gendered hypotheses you could come up with should also work with the genders switched?
- danieltillett 11y agoNo because of the way genetics works it is much more likely to be the Y chromosome that is lost. First the Y chromosome is under stronger indirect selection than the mitochondria due to asymmetric mating. Second in mammals when two different species have a genetic incompatibility this incompatibility manifests in the male offspring. Both of theses point towards male Neanderthal female African as the way this hybridization happened. Edit. I should add the scientific paper behind this New Scientist article proposes a precise genetic mechanism for how the Neanderthal Y chromosome is lost which is further evidence the loss is due Y Chromosome incompatibility.