The number of individuals that make up a Pygmy Marmoset group or family unit can range from two to nine, with five being the typical number of members in a group. In spite of the fact that primates are predominantly social creatures, there have been documented instances of primates of both sexes behaving in a solitary manner while free-ranging in their natural environments. The family units are headed by one dominant female, who exercises unquestioned authority over the other members of the group. A reproductive male, a male in the second position of command, and the offspring from one to four litters produced by these two. Except for infants, who are not considered part of the dominance hierarchy, the dominant older siblings are the ones over their less-experienced younger siblings. The dominant male of the domain is the head of the family’s males in general. It is possible to identify dominant individuals by observing which animals push other animals away from gum feeding sites; the dominant individual will always consume gum first.
Similar to other primates, pygmy marmosets engage in social behaviors such as grooming, huddling, and play on a daily basis. The members of the group will take turns cleaning each other and picking off any stray bugs that may have landed on them during their rest periods throughout the day. It is the responsibility of the sub-females to groom the dominant female. This is a common form of social interaction between members of the same family unit and consists of several Pygmy Marmosets remaining in close proximity to one another while they are resting. The majority of people who play are considered children and sub-adults; this activity can be done alone or with other people. In groups of two or three marmosets, social play consists of activities like chasing and roughhousing with one another. Young Pygmy Marmosets will engage in playful behavior during periods of rest, which occur later in the morning and earlier in the afternoon.