Ancient lineages in the genome: A response to Fagundes et al
To the Editor: In their recent report (1), Fagundes et al. support a model of human evolution in which anatomically modern humans completely replace all local archaic populations of the genus Homo. Fagundes et al. assert that regions of the human genome showing ancient ancestry are not unexpected under their “African replacement” model. The authors cite this premise as a refutation of our misrepresented conclusion (2) that genomic regions with ancient ancestry should be taken as evidence of admixture with archaic populations. Instead, what we concluded is that genomic regions showing ancient ancestry do not support a particular implementation of African replacement, which we call the “single origin” model (2). The single origin model specifies that all modern humans descend from a small, isolated African population. Fagundes et al. (1) estimate a large ancestral population size, which also poorly fits the expectations of our single origin model.
We have stated that genomic regions reflecting admixture events are identifiable by a combination of high levels of haplotype divergence and elevated linkage disequilibrium (2, 3). We cite several instances of this pattern documented throughout the genome, which are statistically supported as being incompatible with a simple African replacement model (2). Each of the 50 regions resequenced by Fagundes et al. (1) consists of only 500 base pairs and therefore contains little information on the size of linkage disequilibrium blocks. Although the model-testing approach by Fagundes et al. is a constructive step forward, comprehensive tests of human evolutionary models await the analysis of datasets comprising larger genomic regions and sample sizes.
Footnotes
- †To whom correspondence should be addressed. E-mail: dgarrigan{at}oeb.harvard.edu
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The authors declare no conflict of interest.
- © 2008 by The National Academy of Sciences of the USA
