As far as I know all human variation is demonstrably caused by little more than the intensity of expression of possibilities extant already in the genome. Despite partial speciation, we did did not complete sufficient physical speciation for typical classification because our primary means of speciation migrated from the physical to the conceptual, and the conceptual is highly affected by the distribution (norm) and therefore physical expression required little physical mutation in the genome, only substantial modification of the mind post birth. These changes have been consistently selected for whenever possible and they universally favor selection for youthfulness (fertility), which is achieved by delaying the intensity of maturity. A point which asians have unfortunately probably exceeded and whites have approached with dangerous proximity.