try this the out of africa theory depends on the proposition that homo sapiens developed from homo erectus - in africa and then migrated outwards through eurasia and to other parts of the world.
these theories were based initially on evidence of skulls and then later carbon dating and DNA studies.
as our ability to unlock the human genome evolves and DNA studies become more sophisticated our underaanings may change
one of the views is that homo sapiens developed in multiple regions. if you want to assume homo erectus as the "parent" you are tracking so many years back that you have to make a lot of assumptions.
evidence around multiregional development of homo sapiens:
Fossil Evidence: Some scientists argue that certain fossil finds represent intermediates between erectus, Neanderthals and modern sapiens. They argue that the physical differences between these groups represent regional differences. For instance, some modern cold-adapted populations have features similar to the Neanderthals. They argue that many fossil finds cannot easily be classified as belonging to one group or the other because they are regional variants of a single species.
Mitochondrial DNA: While the mtDNA from Neanderthal remains are substantially different from modern human in some cases the differences are less than those observed between chimpanzee subspecies. Some scientists suggest this could mean that the Neanderthals were different subspecies, but still belong to the same species as anatomically modern humans.
Y-Chromosome: While an analysis of both mtDNA and Y-chromosomes sequences both suggest an African origin, the results were not entirely consistent, suggesting there are still flaws in our understanding and the data may not be conclusive. Also Y-chromosome analysis indicated a later expansion back into Africa from Asia, demonstrating there was gene flow (interbreeding) between regions and in both directions.
Other Genetic Evidence: Analysis of some sequences on the X-chromosome suggest a much earlier African origin more consistent with the departure of Homo erectus from Africa. There is also some genetic evidence that gene flow (interbreeding) was not geographically limited. A recent African origin would have seen gene flow out of Africa, but there is also evidence of gene flow from Eurasia back into Africa.
