Gene Expression

Out of Africa model most likely

Statistical evaluation of alternative models of human evolution:

An appropriate model of recent human evolution is not only important to understand our own history, but it is necessary to disentangle the effects of demography and selection on genome diversity. Although most genetic data support the view that our species originated recently in Africa, it is still unclear if it completely replaced former members of the Homo genus, or if some interbreeding occurred during its range expansion. Several scenarios of modern human evolution have been proposed on the basis of molecular and paleontological data, but their likelihood has never been statistically assessed. Using DNA data from 50 nuclear loci sequenced in African, Asian and Native American samples, we show here by extensive simulations that a simple African replacement model with exponential growth has a higher probability (78%) as compared with alternative multiregional evolution or assimilation scenarios. A Bayesian analysis of the data under this best supported model points to an origin of our species ~141 thousand years ago (Kya), an exit out-of-Africa ~51 Kya, and a recent colonization of the Americas ~10.5 Kya. We also find that the African replacement model explains not only the shallow ancestry of mtDNA or Y-chromosomes but also the occurrence of deep lineages at some autosomal loci, which has been formerly interpreted as a sign of interbreeding with 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.

Comments

  1. #1 Alan Kellogg
    October 31, 2007

    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.

  2. #2 John Emerson
    November 1, 2007

    Wiki: “Most mainstream scientists consider the Almas to be a purely legendary creature.”

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