"Out of Africa" theory. Of course it's just a theory, but makes sense when you read upon it. Though they have discovered human remains in China and Spain dating back to before the ones in Africa. So who knows for sure, but we all originated from one place, common ancestor, and spread out from there
If Native Americans from murica start foking like rabbits and start crapping b2b kiddos, like 6-8 kids per woman I'd say around 100-200 years before murica gets populated by over 1 billion of dem Gud luck and have fun y'all.