“Mason notes that our ancestors migrated at levels that most people grossly underestimate, leading to far more genetic mixing than people typically assume. She points out that our current understanding of DNA undermines a lot of assumptions that arose from observing external traits, such as skin color, nose shape, and eye shape, since such traits can arise from the same genetic allele but be inherited from entirely different people. Furthermore, thanks to the random genetic recombination that happens with every new generation, 75 percent of your genetic makeup is attributable to only 5 percent of your ancestors. A 23andMe test will tell you about only 8 percent of your ancestors, because they’re the only ones left represented in your DNA today. In fact, it’s possible that two dark South Africans can be more genetically divergent from one another than one of them is from a white Swede.”