X-chromosomal diversity may reflect climate (when considering human expansion from Africa)

Abstract

AbstractA decreasing of diversity with increasing distance from Africa has been interpreted as a signal of modern humans having expanded (across the globe) from Africa. Research is consistent with a climatic signal being present in mitochondrial diversity, but not in other genetic diversities (e.g., X-chromosomal) or cranial diversity. Some of that research involved adjusting diversity for distance from Africa, and seeing whether this adjusted diversity is associated with climate. The choice of African location which the distance from Africa is measured from may affect whether adjusted diversity appears to be related to climate. To bypass this potential effect of location, some analyses in the present study featured only populations outside of Africa. Other analyses included African populations. The present study used diversities, distances, and minimum temperatures from beforehand. Autosomal, X-chromosomal, and cranial diversities were adjusted for distance from Africa. Y-chromosomal diversity was adjusted for distance from Asia because previous research suggested that Y-chromosomal microsatellite heterozygosity offers more support to expansion from Asia (than Africa). Whether populations were worldwide or only outside of Africa, adjusted X-chromosomal diversity increased with minimum temperature. Other adjusted diversities were not related to minimum temperature. Perhaps previous research found no indication of a climatic signal in X-chromosomal diversity because of two populations, one of which likely had an atypical adjusted diversity for their minimum temperature. These populations may have led to heteroscedasticity and the climatic signal being obscured.