We indeed have to take into account that the African origin of humanity only became accepted after the mid-20th century. Very old (the australopithecus) fossils started being found in the mid-1920s in context with tools, and were only collected in quantity by Leakey in the mid-50s. So the "tree of evolution", including also very old fossils of Homo Sapiens, that would lead to the out of Africa hypothesis is relatively recent. Homo Sapiens fossils dated as older than 100000 years were being argued about in the late 1960s. No surprise then that the out-of-Africa theory to "settle" the question of the origins of humanity only got its roots in the 70s.
What I am complaining is that, given this new evidence of even older evolution and broader diversity of humanity collected through the preceding 50 years, most researchers in this field in the 70s and after could not do anything better that then posit a linear evolution with a species replacing others! If there are older fossils in Africa, then a "great replacement" must have started from there. So that there is a neat evolution tree. They still lived within that limited mental framework that saw mixing as inconceivable. That still regarded morphological distinct fossils as different races of man (or rather, its ancestors) unable to mix. So this "out-of-Africa" theory of global replacement of populations was created and quickly became hegemonic after the 1970s. Even as other people, like , were denying the existence of current distinct "human races" and saying that we are all genetically mixed wihy each other now (and of course can mix).
Back in the 1970s we long knew of Homo Erectus fossils with an accepted age of one and a half million years from east Asia. Clear evidence of a previous spread of mankind through the largest two linked continental masses. We knew that these ancestors had developed cultures, deliberate burials, tool use, layers of occupation in several places through Eurasia with other species (just as had also been found in Africa). So why even make up a theory that the old were wiped out by a new species?
But the current theories get worse. If you are willing to look at the circumstances with a critical mind, they beg a question: "if early humans (homo erectus) spread nearly two million years ago and reached as far as Oceania - we have fossils there indicating an interval of perhaps 100000 years for that spread, possibly less - then why should modern humans evolve in a single place and then spread from there?" What was blocking the (literal) intercourse of populations in the one and half million years between the initial spread and homo sapiens? If early hominids could spread, and if hominids could mix, then
how can there be a single place of origin and a single later migration event to spread the "new race"?
The late out-of-Africa theory does not make sense. It never made sense. If there was mixing, that mixing must have gone on for all the time these hominids were evolving, not after some momentous single event of migration. Because migrations and mixing must have been going on all the while.
There was nothing stopping that. The red sea didn't magically part Africa from Eurasia without us noticing in the geological record during that time. And early humans managed to cross the sea anyway - they got to Java. Imo if there are no bones showing ongoing migrations and mixing during that nearly one million years in other places, it's because they haven't been found yet. Not because magically homo sapiens evolved alone in some hidden valley in Africa and then took the world in a rampage. Geological and climate conditions and not conductive to the preservation of fossils in many regions.
Likewise about believing that what is called Denovisians only existed in a small region in central Asia just because fossils that we classified as such were only found there. Or that Neanderthals only existed in western Europe because fossils were only found there - is absurd when the regions there existed in were not physically separated for the hundred of thousands of years they existed. People claiming that enduring separation happened cannot say so based on only having found fossils in those places: absence of evidence is not proof of absence of it happening. People claiming it didn't happen must explain why would these populations not migrate and mix with others.
Then we "discover" that Neanderthals and Denovisians did in fact interbred - hail genetics. And that Neanderthals lived south of the Mediterranean. And so on. Those people who saw lack of evidence as evidence of their theory were wrong. The big mix has been on since the first large migration millions of years ago from Africa.
@PhroX Interbreeding between early humans
as we classify them now in "species" is like virginity: you wither have it or you don't! If you do then there was nothing stopping it going on continuously, which negates the whole late big "out of Africa" migration with a single origin for modern humans. That even earlier humans had spread across the land long before the era proves beyond any doubt that these ancestor were not mobility-constrained. That they did interbred proves they could interbreed. Put the two together and the theory of homo sapiens being a one-off coming up in some isolated region and spreading like wildfire from there becomes unsustainable.
Saying that "there's only x% of genes" is like putting epicycles into the geocentric theory to pretend it could still explain reality as well as the heliocentric one. "Bad bad geneticists have undermined my beloved theory - I will just say that most of the genes of modern humans come from these fossils I promote as earliest modern" - pick and choose to do that.
No - the whole model is bankrupt. Evolution could not avoid being widespread at that stage of human pre-history.
That most of human evolution happened in Africa is unsurprising - it's the best continent for it in the old world: the second largest after eurasia and one with lots of different regional climates and options to move north-south, so across climate regions, in response to stuff like global warming and cooling, or to flee diseases. But to pretend that this evolution happened in some small region there without constantly leaking from it and mixing about cross the world was always absurd. There was no "dam" preventing it from being a much larger affair across the wold world.
