nor entirely exclusive, in species that demonstrate monogamous pair 
bonding.  A study completed by a University of California at Davis 
psychologist, William Mason, revealed that the monogamous titi monkeys 
do not remain together for life, nor are they always faithful to their current 
mate.  Some species of gibbon, however, display what could be termed as 
long term fidelity and life-long pair bonding within their monogamous 
pair bonds.  All non-human primates that form monogamous pairs live in 
arboreal settings, such as the familiar gibbon.  Most tend to display, 
therefore, adaptations to life in the trees, such as brachiation.  The 
monogamous pairs tend to be territorial, defending their arboreal settings 
from and not tolerating other adults of the same species in their territory, 
since they can not free-range as other primates do.  Compared to other 
breeding structures in primates, monogamous pairs demonstrate minimal 
sexual dimorphism, meaning that the two sexes are nearly identical in 
morphology, particularly in body size.
	The second type of sexual strategy that is found in primates is a 
structure composed of several adult males, several adult females, and all 
dependent young.  Macaques, such as the familiar Rhesus monkey, 
mangabeys, savanna baboons, vervets, chimpanzees, some lemurs, and 
some spider monkeys make use of this sexual strategy as their "state of 
nature."  In all species that have multiple adult males and females, tension 
between males, caused by competition by the males for the females, 
results.  In response to this tension a dominance hierarchy arises to form a 
social structure.  Within this system, also as a result of multiple males 
competing for multiple females, a process known as dispersal takes place, 
in which one of the sexes leaves the group.  The members of the sex that 
remain in their natal group, called the philopatric sex, enjoy certain 
advantages, such as establishing long-term bonds that aid in protection, 
collection of resources and elevation of status within the social structure.  
Although there are some exceptions within each species, the multi-male 
and multi-female groups are mostly composed of groups with females as 
the philopatric sex, while only chimpanzees display a consistent trend of 
males as the philopatric sex.  The dispersal of the non-philopatric sex, 
combined with the aforementioned dominance hierarchies, form the basis

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