Further confirmation for unknown archaic ancestry in Andaman and South Asia

Abstract

In a recent paper, we have derived three main conclusions: i) that all Asian and Pacific populations share a single origin and expansion out of Africa, contradicting an earlier proposal of two independent waves; ii) that populations from South and Southeast Asia harbor a small proportion of ancestry from an unknown extinct hominin - different from the Neanderthal and the Denisovan - which is absent in Europeans; and, iii) that the characteristic distinctive phenotypes (including very short stature) of Andamanese do not reflect an ancient African origin, but have resulted from strong natural selection on genes related to human body size. Although the single wave out of Africa and single origin for Asian and Pacific populations have been confirmed, the existence of admixture with an extinct hominin has been challenged by Skoglund et al., as they were unable to replicate our results in their data sets. While we had used a wide variety of statistical methods and data sets from diverse populations to draw our inference, Skoglund et al. have used only one method (D-stats, for the whole genome, not specifically for the relevant genomic regions) and compared only with the Asians, not even with the Europeans. Skoglund et al. have alleged that our statistical treatment of the data was faulty and have pointed out some possible sources of error. We have reexamined our data focusing on possible sources of error flagged by Skoglund et al. We have also performed new analyses. The reexamination and new analyses have bolstered our confidence that our earlier inferences were correct and have resulted in an improved model of introgression of modern humans with a hitherto unknown archaic ancestry. We also propose a possible reason for the inability of Skoglund et al. to validate our inference.