> This suggests that hybrids from Homo sapiens and Neanderthal female parents were non-viable; perhaps only male Neanderthals and female Homo sapiens could mat

> 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.