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You should add to this the observation that there is a lack of Neanderthal mitochondrial DNA in modern humans. This suggests that hybrids from Homo sapiens and

by pcrh 3y ago

You should add to this the observation that there is a lack of Neanderthal mitochondrial DNA in modern humans. This suggests that hybrids from Homo sapiens and Neanderthal female parents were non-viable; perhaps only male Neanderthals and female Homo sapiens could mate to produce offspring. The implication is that mating between these two groups may have been twice as frequent as is suggested just by considering the amount of Neanderthal DNA in modern humans.

im3w1l 3y ago
> This suggests that hybrids from Homo sapiens and Neanderthal female parents were non-viable; perhaps only male Neanderthals and female Homo sapiens could mate to produce offspring. That's one possibility, but it could be that they were perfectly viable but the matrilineal lineages just ended at some point. Maybe they were x% less fit or maybe the ended to due pure chance. Like maybe the daughter daughter daughter only had sons and that was the end of that mitochondial dna. It's my understanding that mt-dna and y-dna are subject to much more random genetic drift, and thats one reason that their genetic material is gradually replaced by more reliable autosomal dna.
philwelch 3y ago
This isn’t the only possible explanation. If you compare Y-chromosome haplogroups to mitochondrial haplogroups there are similar cases within even more recent human populations. For instance, European populations almost exclusively come from R1a and R1b Y-chromosome haplogroups that probably originated with the Proto-Indo-Europeans of the Pontic Steppe. However, there are still European mitochondrial haplogroups corresponding to much earlier European populations. In other words, the carriers of the R1a and R1b haplogroups specifically replaced the male population of prehistoric Europe. These were all modern humans so there’s no reason they wouldn’t be able to have viable offspring the other way around. That’s just not how the Proto-Indo-European migrations seemed to work out. That’s not to say that the same thing happened with the Neanderthals. We can piece together the story of the PIE’s from archeology, linguistics, and population genetics to a much fuller degree than the story of the Neanderthals. But it does go to show that you can have significant interbreeding events between human populations that do end up happening exclusively one way around.

by pcrh 3y ago

im3w1l 3y ago

> This suggests that hybrids from Homo sapiens and Neanderthal female parents were non-viable; perhaps only male Neanderthals and female Homo sapiens could mate to produce offspring. That's one possibility, but it could be that they were perfectly viable but the matrilineal lineages just ended at some point. Maybe they were x% less fit or maybe the ended to due pure chance. Like maybe the daughter daughter daughter only had sons and that was the end of that mitochondial dna. It's my understanding that mt-dna and y-dna are subject to much more random genetic drift, and thats one reason that their genetic material is gradually replaced by more reliable autosomal dna.

philwelch 3y ago

This isn’t the only possible explanation. If you compare Y-chromosome haplogroups to mitochondrial haplogroups there are similar cases within even more recent human populations. For instance, European populations almost exclusively come from R1a and R1b Y-chromosome haplogroups that probably originated with the Proto-Indo-Europeans of the Pontic Steppe. However, there are still European mitochondrial haplogroups corresponding to much earlier European populations. In other words, the carriers of the R1a and R1b haplogroups specifically replaced the male population of prehistoric Europe. These were all modern humans so there’s no reason they wouldn’t be able to have viable offspring the other way around. That’s just not how the Proto-Indo-European migrations seemed to work out. That’s not to say that the same thing happened with the Neanderthals. We can piece together the story of the PIE’s from archeology, linguistics, and population genetics to a much fuller degree than the story of the Neanderthals. But it does go to show that you can have significant interbreeding events between human populations that do end up happening exclusively one way around.