Bells now accepts that the pure biology i posited is correct, not the little 'kink' she thought it was. Iceaura postulates that the sapien females were desired by the neanderthal males. I agree, they likely were. Indeed, we see before they became fully neanderthal, circa 220,000 KYA (proto-neanderthal) they were still breeding with proto-sapiens, as per Bells post showing proto-neanderthals mated with proto-sapiens, with the proto-sapien mtDNA overtaking and becoming the sole mtDNA in the proto-neanderthal tribes. But that was then. More recently, circa 60-40 KYA, when sapien invasion occurred, no such sapien mtDNA was incorporated into the neanderthal genome, and they remained with solely the proto-sapien mtDNA, since changed into the neanderthal mtDNA by further modification making it very much more distinguishable. It is this neanderthal mtDNA, the 'advanced' (more recent) mtDNA, that was not injected into the sapien lineage when the sapien tribes invaded the neanderthal tribal areas across Eurasia. Certainly when the proto-neanderthal and proto-sapien tribes looked more alike and lived in proximity, there was still some mating overlap. Apparently, the proto-sapiens females were sufficiently 'better' than the proto-neanderthal females, that that mtDNA became fixed in the neanderthal lineage (quite the woman). However, we've been talking about the full neanderthals, and how it came about that their mtDNA is not in the modern sapien lineage, and their Y-chromosome not in the modern sapien lineage (so far as we know - still waiting to find that anomalous one!) Biologically, there are two methods for those results: Neanderthal males mated with human females, but the male babies did not survive (leaving no trace of the neanderthal Y chromosome; and no trace of the neanderthal mtDNA); OR Sapien males mated with neanderthal females, but the female babies did not survive (leaving no Neanderthal Y chromosomes, and no trace of the mtDNA thereafter when the hybrid male grew up and mated) Of those two, I've suggested the latter is more likely, though it does require female infanticide. Likewise, the first scenario (espoused by Bells) requires either male infanticide or death of the male in-utero. Since female infanticide is a well-known sociological phenomena, it appears more probable to me than death of a male fetus when in-utero in a female sapien, but no death of the fetus when in-utero in the neanderthal female. Of course, it is possible that both 'mechanisms' were at play, though I suspect that future information will more likely support my scenario.