the formation and changing of social group structure in primates to attend to aggressive 
interactions, to minimize the amount of antagonistic interactions, and to protect the health of 
the group members. It may be helpful to permit animals to become acquainted before they are 
placed in the same group — for example, housing them in proximity to each other, or placing 
a potential new group member into the social group in a smaller cage for a time before 
releasing it. 
GENDER OF THE ANIMAL 
Post-pubertal males of many species exhibit aggression toward other males, and for this 
reason they cannot be housed together. 
AGE OF THE ANIMAL 
The social needs of animals vary across the life span, even in gregarious species. Data exist 
for many species showing that appropriate social stimulation is important for normal infant 
development. Special consideration thus needs to be given to the normal parental rearing of 
infant animals, unless the focus of the research itself precludes this. At the other end of the 
life span there is evidence in some species (including some nonhuman primates) for a decline 
in sociality with old age. Thus, the recommendation for social companionship must be 
flexibly and appropriately applied. 
TYPE OF SOCIAL PARTNER 
To achieve the benefits of social companionship, thought must be given to the optimal type of 
social partner. Even in gregarious species, many competing behavioral processes influence 
the positive or negative nature of social relationships. The formation of hierarchical 
dominance relationships may affect the relative benefits of social housing for each individual. 
Subordinate animals, for example, may have more difficulty obtaining food or freely moving 
around in the spatial environment. This concern is most evident in newly formed social 
groups, where it can be expected that the influence of dominance will subside somewhat over 
time unless desired resources such as food or water are limited. It can also be assumed that 
the sex and age of the partner will influence the nature of social relationships that are formed, 
and thereby the relative benefits/costs of sociality for each individual. Data are needed to 
weigh the benefits to animal and researcher of social housing against negative consequences 
(disease transmission, aggression). 
RESOURCE AVAILABILITY 
When animals are housed socially, careful consideration must be devoted to the manner in 
which resources are provided. Food and water may have to be presented ad libitum to prevent 
competition for limited resources, or they may have to be presented in a dispersed manner, so 
there will be less competition for resources at a restricted site. The ideal environment would 
provide individuals with the opportunity to separate themselves from social companions while 
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