My understanding of what you're saying is that you have no actual point. Is the American culture/society originally not of European origins because the founding Europeans were no longer in Europe?
The fact of the matter is YOU DO NOT KNOW if the original humans that migrated to human were still brown or black-skinned like their African forebears. Why do you automatically assume that they had?
As for you're comment 'in a span of 100 000 many genetic mutuations would have occurred so that by the time humans reached africa they wouldnt have looked "african" anymore', there are a number of flaws I can point out:
First of all, the name of this thread is "african ORIGIN of chinese civilization", not "chinese civilization 100,000 years AFTER it's origin". Therefore, whatever mutations occured among said populace over 100,000 since it's origin is irrelevant to this discussion.
Besides that, I live in Calgary & see Asian people EVERYDAY who have remarkably "Negroid(flat-flared) noses.
Also, how in the world do you KNOW there was no such thing as CULTURE 60-100,000 years ago since you didn't exist?

I guess this sums up the basis of your original post: "The point that I am trying to make is that even though there were africans in ancient china, those africans had already separately themselves (culturally) from Africa, so that they were no longer african once they reached china"
First off, what are you basing the statement that they'd seperated themselves culturally from Africa ON? You're a zoologist, right? That's not a cultural anthropologist last I checked. Second, you're contradicting yourself by stating "even though there were africans in ancient china", then later stating "by the time humans reached africa they wouldnt have looked "african" anymore". Your basic reasoning being that they were not Africans simply because they were no longer in Africa. Does that mean all the Chinese & other Asian people I see here in Calgary are no longer Asian?