Wednesday, May 19, 2010

Humans Came From Where?

Coherent and incoherent inference in phylogeography and human evolution. 2010. A. R. Templeton, PNAS 107: 14 6376-6381.

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Templeton has determined that a recently published genetic analysis of deep human DNA evolution is mathematically erroneous and formally illogical. The flaws of the analysis are due to the incorrect application of a statistical method known as approximate Bayesian computation (ABC), which led the authors to support the validity of the controversial “Out of Africa” replacement hypothesis in a 2007 paper. Templeton has previously done a 2005 analysis that disputes this model, showing instead a trellis relationship between different human populations, supporting gene “admixture,” or intermingling.

Templeton got the notion to re-address the Fegundes paper when he noticed claims in a student’s paper using Bayes factors that were just too good to be true. Researching Bayes factors in the primary statistics literature, he found a 1999 paper that the probabilities generated by Bayes factors can be incoherent (result in conclusions that violate logic). He then re-read the Fegundes paper.

“When I first read the paper, I thought something was wrong with it, but I’ve got to admit I didn’t see the incoherence,” Templeton says. “I just saw these probabilities, and they didn’t make any sense to me, but I couldn’t quite pin it down. As soon as I read the 1999 paper, I went back to the 2007 one, and I saw that it was massively incoherent. It arrives at probabilities for different models of human evolution that violate the constraints of formal logic.” link