Primates occupy most of the all biomass of the seed dispersors in tropical forests. Among primates, two main feeding techniques are found; one is a type of processing the fruits with cheek pouches and another is a type of swallowing the fruits without cheek pouches. The cheek pouches are one of the main morphological features of Old World monkeys, however, neither the apes nor New World monkeys have cheek pouches.
Almost all of Old World monkey species have matrilineal societies, while almost of the primate not having cheek pouches have non-matrilineal societies. Some of apes and atelines have patrilineal societies.
Since the appearance of Cercopithecoid having cheek pouches in early Miocene, the relative species diversity of the hominoids in the primate community has been decreasing. This dramatic change of primate community in the Old World might be due to the differences in the efficiency of exploitation for the food resources in the forests between primates having and not having cheek pouches.
