So what we can answer [as geneticists] is questions about biology, about biological ancestry. But to make any sense of that historically we have to contextualize it - the archaeology, the linguistic pattern, even the climatology.

We are all Africans under the skin.

DNA ties us all together we share ancestry with barracuda and bacteria and mushrooms, if you go far enough back.

Imagine you're copying a very long document, and occasionally you'll put an A where there should be a C. And that mistake has been translated down through the generations, and more mistakes have accumulated. So the longer the lineage has been in existence, the more mistakes the sequence is going to have.