Does biological diversity indicate modern human expansion across Africa?

Regardless of whether modern humans originated in a single region of Africa, or across the continent, we may have experienced a significant expansion which crossed Africa and spread to the other habitable continents. It is unclear if we expanded across Africa, however, this manuscript highlights methodological issues in previous research on the topic. Moreover, we are known to lack clarity on where the expansion would have begun. The present study explored the expansion by examining types of diversity in sub-Saharan Africans: cranial shape (13 populations), autosomal (20 populations), X-chromosomal (17 populations), and, adjusting for minimum temperature, mitochondrial (20 populations). For each diversity, i) it was examined if there is a geographical pattern within Africa and ii) the best choices for the origin of the expansion were estimated. A ranking procedure indicated, across diversities, where the expansion originated. Each diversity declined with increasing distance from somewhere inside of Africa. Findings with autosomal diversity appeared to be driven by the datapoint for Somalis. A southern origin was specified by cranial and X-chromosomal diversities. No singular region was identified by autosomal or mitochondrial diversities. Simultaneous examination of diversities indicated an expansion from southern Africa. Admixture is a known obstacle for using diversity to study expansion. It is explained why results might not have arisen from a broad effect of admixture given that i) linkage disequilibrium previously pointed to the south and ii) supplementary analysis with additional measures (which should not broadly be affected by admixture) tentatively indicated a southern origin.