of the social structure in this multi-male, multi-female sexual strategy. The main morphological trait that species of this sexual strategy display is swelling of the genital tissue of females during estrus. Found in many species, such as chimpanzees and baboons, these swellings serve as a visual cue to a female's readiness to mate. With this type of sexual strategy, group size would seem to be difficult to control. As is found in savanna baboons and Hanuman langurs, both of which display this type of sexual strategy, however, two competing forces regulate group size. There is competition within the group for sexual partners and food, which results in the dominance hierarchies and tends to reduce the group size. There is also competition with other species, mostly predators, which conversely encourages a large group size to aid in the protection of the group. These two forces balance at different points in different species and even at different places within species, depending upon environmental factors. The third type of sexual strategy found in primates, and the strategy that is by far the most prevalent "state of nature," is composed of one actively mating adult male, multiple adult females and all dependent young. This type of polygyny is found in gorillas, guenons, patas, some spider monkeys and some pottos. Two striking similarities are found among species that practice polygyny. The first is a marked sexual dimorphism. Males are, on the average, considerably larger than females. Males of the Gorilla gorilla species generally weigh 400 pounds, while females generally weigh approximately 200 pounds. Orangutans also display this strong sexual dimorphism of males being roughly twice the size of females. This is an evolutionary development to allow the males to defend their harem of females. The second similarity is that in a polygynous social structure, males, once they reach adulthood must leave the group, much like the dispersion found in the organization with multiple adult males and females. Because only one actively mating adult male is allowed per female group, usually called a troop, there is an excess of males. These males often form a bachelor group of their own that loses and gains members as the members take over or are ejected from various female troops in the area. Note that the troop is, indeed, a female