In a new book, anthropologist and neuroscientist Melvin Konner explores the biological evolution of human behavior and specifically the behavior of children, looking at how “play” affects our development. Konner found that the smartest mammals are also the most playful, indicating that the traits have evolved together. “Combining as it does great energy expenditure and risk with apparent pointlessness, [play] is a central paradox of evolutionary biology,” he writes.