Competition is not ignored in his work: the original focus of de Waal's research, before he was well known, was aggressive behavior and social dominance. Whereas his science focuses on the behavior of nonhuman primates (mostly chimpanzees, bonobos, macaques, and capuchin monkeys), his popular books have given de Waal worldwide visibility by relating the insights he has gained from monkey and ape behavior to human society. With his students, he has also worked on elephants, which are increasingly featured in his writings.