Stearns says globalization, immigration, cultural diffusion and the ease of modern travel will gradually homogenize the human population, averaging out more and more people’s traits. Because recessive traits depend on two copies of the same gene pairing up in order to get expressed, these traits will express themselves more rarely, and dominant traits will become the norm. In short, blue skin is out. Brown skin is in.

Already in the United States, another recessive trait, blue eyes, has become far less common. A 2002 study by the epidemiologists Mark Grant and Diane Lauderdale found that only 1 in 6 Americans had blue eyes, down from more than half of the U.S. population being blue-eyed just 100 years ago.