, a new genome blogger questions the existence of Amerindian-like admixture in Europe. I am generally well-disposed to anyone who tries their hand at analysis of genetic data. On the other hand, if one accuses me of writing a series of posts "chock-full of stupidity", then there's a good chance I might respond. This should also be useful for anyone wishing to understand the evidence for this admixture.proposes that the "Amerindian-like" admixture in North Europeans is misunderstood and can be in fact explained by the existence of "North European-like" admixture in Amerindians. In support of this, he presents the results of an F4 Ratio estimation analysis which suggests that there isF4 Ratio estimation produces admixture estimatesbut does notthe existence of such admixture. The admixture estimates are as good as the relationship proposed for a particular set of populations. If the relationship is nonsensical, so will be the admixture estimates.According tothe following relationship holds, with A=Sardinian, B=Orcadian, C=Dai, and O=Yoruba, with X=Amerindians.The existence of Amerindian-like admixture was argued by Patterson et al. (2012) on the basis of the following F3 statistic (right):F3(European; Sardinian, Amerindian)which is signifantly negative for North Europeans. Now, consider the value of this statistic forphylogeny.F3(B = North European; A = Sardinian, X = Amerindian)In the above figure I color-coded the path from B=North European to A=Sardinian (red) and from B=North European to X=Karitiana (green, if it goes via the supposed "North European" admixture, or blue, if it goes via the "Amerindian" admixture). The value of the F3 statistic is then the weighted sum of the overlap of the red/green and red/blue paths:F3(B; A, X) = αBZ+(1-α)(BZ+ZW)where BZ and ZW are drifts along the paths indicated in the figure. This statistic is then always, since the common segments in the graph are traversed in the same direction.