Statistical evaluation of alternative models of human evolution:
An appropriate model of recent human evolution is not only importantto understand our own history, but it is necessary to disentanglethe effects of demography and selection on genome diversity.Although most genetic data support the view that our speciesoriginated recently in Africa, it is still unclear if it completelyreplaced former members of the Homo genus, or if some interbreedingoccurred during its range expansion. Several scenarios of modernhuman evolution have been proposed on the basis of molecularand paleontological data, but their likelihood has never beenstatistically assessed. Using DNA data from 50 nuclear locisequenced in African, Asian and Native American samples, weshow here by extensive simulations that a simple African replacementmodel with exponential growth has a higher probability (78%)as compared with alternative multiregional evolution or assimilationscenarios. A Bayesian analysis of the data under this best supportedmodel points to an origin of our species ~141 thousand yearsago (Kya), an exit out-of-Africa ~51 Kya, and a recent colonizationof the Americas ~10.5 Kya. We also find that the African replacementmodel explains not only the shallow ancestry of mtDNA or Y-chromosomesbut also the occurrence of deep lineages at some autosomal loci,which has been formerly interpreted as a sign of interbreedingwith Homo erectus.
I don't have time to read this paper now, so I hope John Hawks blogs it soon. Obviously I'm curious as to how they explain deep lineages, Bruce Lahn's Neandertal introgression paper attempted to check for dynamics such as balancing selection.
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A fact to consider when talking about Human-Neanderthal interbreeding.
The Savannah Cat is the product of breeding domestic cats with servals, followed up by "fixing" the desired traits in the new breed through additional breeding. The thing to note here is that the great majority of the initial cat-serval breeding attempts failed to produce so much as a pregnancy. Of those that resulted in pregnancies; most ended in miscarriage, most of the successful pregnancies in mules, and only a small number in fertile specimens. Thus out of all the attempts to breed cats and servals only a rare few resulted in animals that could then be breed in turn.
If sexual activity occurred between Humans and Neanderthals (more likely than you think, for Neanderthals do appear more human than some would expect) it is most likely nothing came of it, there were a few short term pregnancies, a rare few pregnancies resulted in sterile young, and an exceedingly rare number in fertile young.
Then there's a story out of Russan Central Asia in which an Almas woman (see Wikipedia under "Almas" for details) bore a number of children for a Human man, three of which survived to maturity, and one of whom is known to have had children of his own. According to local accounts the Almas' description rather closely resembles most Neanderthal reconstructions.
Wiki: "Most mainstream scientists consider the Almas to be a purely legendary creature."