About 7,500 generations have passed since our ancestors lived on the savannas of eastern Africa

Though just a little dated at this point, I did enjoy Mapping Human History: Genes, Race, and Our Common Origins by Steve Olson which I have just finished. Page 29.

In a way, the details of how modernity in humans arose are not important. What must count as one of the most profound biological insights of all time is the recognition of our remarkable genetic similarity. About 7,500 generations have passed since our ancestors lived on the savannas of eastern Africa. In evolutionary terms, that's the blink of an eye. The chimpanzees living on a single hillside in Africa have more than twice as much variety in their mitochondrial DNA as do all 6 billion people living on the earth, because today's species of chimpanzees have been in existence much longer than have modern humans.