Modern human expansion from (southern?) Africa: Origin, non-African ancestry, and linearity

Previous research favours the idea that modern humans spread worldwide from Africa. For instance, through autosomal diversity, a geographical area of origin for this worldwide expansion is indicated to entirely be within Africa. It remained to be seen if this indication happens for certain variables such as Y-chromosomal diversity. There is disagreement regarding where in Africa the origin is. Perhaps a region of Africa may seem to be the origin because of non-African ancestry rather than the expansion. The present research considered whether some genetic and cranial variables indicate the expansion, and, furthermore, where in Africa the expansion started. Variables included, for example, autosomal diversity (in sub-Saharan Africa) which was adjusted for non-African ancestry, Y-chromosomal diversity, and cranial sexual size dimorphism. For each variable, it was seen if the estimated area of origin was solely in Africa. Moreover, to generally estimate the origin, a centroid was calculated from potential origins which were obtained in the present, and past, research. The area of origin was completely within Africa for each variable except one – for Y-chromosomal diversity, the area was possibly in Asia only. The centroid of the potential origins was in southern Africa, consequently supporting a southern African origin. The autosomal diversity of sub-Saharan African populations, adjusted for non-African ancestry, indicated a southern African origin. The adjusted diversity appeared to start declining from about 2,000-3,000 km away from the origin – this non-linear pattern may be explained by travelling which happened after the expansion, or the expansion entering locations in Africa which were already populated, to differing extents, by modern humans.