“Scientists have found that nomads who inherited the form of a particular gene linked to extroversion (specifically, to novelty-seeking) are better nourished than those without this version of the gene. But in settled populations, people with this same gene form have poorer nutrition. The same traits that make a nomad fierce enough to hunt and to defend livestock against raiders may hinder more sedentary activities like farming, selling goods at the market, or focusing at school.”