 The simplistic ideas about race held by eugenicists did not hold up to scientific scrutiny. Twentieth century developments in fields like human evolution, anthropology, and sociology proved that races were not so cleanly distinguishable—that there were no racial atomic numbers that carved up Black and White in the same way that proton number neatly distinguished gold from mercury. Still, interest in race and genetics persisted. Insights from the study of human evolution revealed how the earliest humans moved out of Africa roughly 70,000 years ago in a series of migrations, some moving east across the Asian continent, some moving north up into what is now Europe, some eventually crossing the Bering Strait and entering the Americas. As these human populations moved about, they encountered very different environments with unique selection pressures (Herrera and Garcia-Bertrand 2018). What counted as adaptive in the fjords of Northern Europe looked quite different from what was adaptive in the deserts of Northern Africa, and so the human populations over time adapted to the distinct environments—some developing darker skin while others grew lighter, some developing a resistance to cholera while others developed a resistance to malaria.