the last male common ancestor of all eurasians and most africans existed around 80,000 years ago. the last female common ancestor of all eurasians and some africans existed sometime around 80,000 years ago. the smoking gun was probably the toba super eruption. blacks are descended paternally from proto eurasian males that migrated back into africa after the toba eruption and took the woman of the native blacker males belonging to haplogroups a and b.
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