Human evolution has been rapid and sophisticated. But “where do we go from here? Have we attained perfection and ceased to evolve? Many geneticists think that is very unlikely, though few find it easy to say where we are headed or how fast. Until the agricultural revolution 10,000 years ago, people used to live in small populations with little gene flow between them. That is the best situation for rapid evolution, said Sewall Wright, one of the founders of population genetics. But Sir Ronald A. Fisher, another founder of the discipline, argued that large populations with random mating — just what globalization and air travel are helping to bring about — were the best fodder for rapid evolution. Which of them is right? No one really knows.”