Voyage of Darwin's Beagle: On the Future of Species season 1 episode 2

Episode title: Low Life on the Ladder of God

When Darwin set foot in Rio de Janerio he witnessed the brutality of slavery. Brazil is a melting pot of genetic diversity. All fossil and genetic evidence points that Africa is the home continent where modern Humans originated about 200 thousand years ago. As Humans spread and colonized new continents genetic diversity eroded gradually proportional to the distance away from Africa. Loss of genetic diversity was because of joint effects of two well understood genetic phenomena known as population bottleneck and founding events.