re: Are we all Africans?

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Would you agree, humanity's origin has nothing to do with the contemporary social construction of race?

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Race is the single most devisive word in the English language. As it is commonly used, Dictionary.com defines it as "a group of people sharing the same culture, history, language, etc.; an ethnic group."

Racists mistakenly apply the biological definition to the modern human species: A population within a species that is distinct in some way, especially a subspecies.

There are no modern human subspecies, only Homo sapiens sapiens. Every living human on this planet is within this species. Humans share 99.5% of their DNA. That means that every difference between any two humans can be attributed to just one half of one percent.

There used to be subspecies of humans extant on earth. For example, Homo sapiens sapiens once lived alongside Homo sapiens neandertalensis and Homo sapiens denisova (temporary name).

These three human subspecies encountered each other and some interbreeding occurred. Only we survived. There is no clear answer yet as to why.

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Or that significant changes occurred in the populations that got out of Africa tens of thousands of years ago from those that remained?

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Significant to the point that subspecies of humans arose? No. Certainly there were adaptive changes that occurred. For example, Neandertals evolved short statures with barrel chests to better cope with the cold climate they inhabited.

However, both modern humans and Neandertals share a common ancestor (Denisovans most likely are a third subspecies of that ancestor), thought to be Homo heidelbergensis. The branching of H. heidelbergensis was in Africa, though. Fossil evidence unearthed in Africa since the first discovery in Heidelberg, Germany (hence the name) confirms this.

While ancestors of the human lineage seem to have left Africa in successive waves beginning as long ago as 1.75 million years, Homo ergaster, there is just no evidence that they evolved into Homo sapiens, or any of its subspecies for that matter, outside of Africa.