ABSTRACT
The two branches of the Catarrhini are the hominoids and the cercopithecoids. They are the world's most successful primates. The descriptions of primate behavior are arranged under these headings: ecology, sociality, and cognition. Distinctive physical features include opposable thumbs and ischial callosities. Many cercopithecoids have fully opposable thumbs in the sense that they can touch the thumb to the tips of other fingers. This makes them capable of more complex manipulations than the New World primates. Male emigration is more common than female, so there is a strong tendency towards female philopatry in Old World monkey societies. Baboon sexual swellings are among the largest and most colorful signals exhibited by any mammal. The graded signal hypothesis postulates a dual function for swellings. Because they grow slowly before ovulation and decrease gradually afterward, they are "probabilistic" indicators of ovulation. The reliable indicator hypothesis holds that the swellings are honest representations of a female's reproductive quality.
