A primatologist's subject is apes. Primatology is the scientific study of primates, which are a group of mammals that includes humans, apes, monkeys, and prosimians. Primatologists study the behavior, ecology, and evolution of these animals in order to gain insight into human behavior. APE is a three-letter word that is used to refer to any member of the hominoid family, which includes gorillas, chimpanzees, orangutans, and gibbons.