The social system of a given species is an outcome of
(1) its social structure, the size and composition of a typical group of that species, and
(2) its social organization, how those individuals are organized (i.e., the patterns of spacing, agonistic and affiliative social interactions, philopatry [whether one or both sexes remain in their natal group], and dispersal [whether one or both sexes move to a new group to reproduce]) that typify that species. Each species also tends to have a characteristic mating system (i.e., the pattern of mating among members of each sex). All of these aspects of primate societies vary widely across the primate order.
The least gregarious primates have what is often referred to as a solitary dispersed social system. In these primates, an adult male’s territory overlaps the territory of one or more adult females, but each individual forages alone and maintains social contact mainly through vocal and/or olfactory communication. These primates are typically nocturnal, foraging at night and sleeping in trees during the day. The mating system in these primates is usually polygynous (i.e., each male mates with multiple females). This type of social system characterizes galagos, lorises, some lemurs, some tarsiers, and orangutans. Notably, orangutans are the only anthropoid primates with a solitary social system.
Bluewire Strategy – Primate Clan
Titi monkeys, owl monkeys, some callitrichids (marmosets and tamarins), and many hylobatids (gibbons and siamangs) are characterized by a pair-bonded social system. Here, one adult male and one adult female form a small social group and defend a territory from other pairs. The mating system in these groups is usually monogamous (only one male mates with only one female), though extra-pair copulations have been observed, and the male usually participates in offspring care, which is unusual for male mammals ).
Many marmosets and tamarins live in one-female multi-male groups characterized by cooperative breeding. In this type of system, usually, only one female breed, and that female suppresses the reproduction of any subordinate females via aggression and/or pheromonal (olfactory) signals. Usually, there is more than one breeding male, thus the mating system is polyandrous, a rarity among mammals. Some or all of the individuals in these groups participate in offspring care and this social system is thus often called cooperative polyandry.
One of the most common primate social systems is the one-male group, which characterizes most colobine monkeys, most guenons, patas monkeys, howler monkeys, and some gorillas. Here, a single resident adult male defends a group of (usually) philopatric, related females from other males and, while his tenure lasts, enjoys exclusive mating access to those females (i.e., polygyny).
Sometimes called harems, these groups are always at risk of takeover by non-resident males, who typically form all-male groups while awaiting their chance to become a resident male. Often, takeovers are accompanied by infanticide, in which the new resident male kills the young infants in the group. This behavior has the effect of bringing the mothers back into estrus (sexual receptivity) sooner than they would have otherwise.
Bluewire Strategy – Primate Clan
Also common among primates are multi-male multi-female groups, in which multiple individuals of each sex form large social groups in which the mating system is usually polygynandrous (i.e., both males and females are polygamous in that they mate with multiple members of the opposite sex). These are the largest groups of primates, and usually quite complex socially, with differentiated social and kin relationships among group members.
This type of social system characterizes many monkeys, including macaques, most baboons, vervet monkeys, mangabeys, capuchins, squirrel monkeys, woolly monkeys, and some colobine monkeys, as well as some lemurs-most notably the ring-tailed lemur and sifaka. In most of these species, females are philopatric and males disperse.
Similar to multi-male multi-female groups are the fission-fusion communities of chimpanzees, bonobos, spider monkeys, and some other ateline monkeys. Fission-fusion communities are less cohesive than typical multi-male multi-female groups. These groups occupy very large home ranges in which temporary foraging parties cleave and coalesce over time with changes in resource availability and female reproductive condition. These social systems are typically characterized by female dispersal and male philopatry.
Bluewire Strategy – Primate Clan
The most complex type of social system found in primates, and in mammals as the whole, is the multi-level society (also known hierarchical or modular society) characterizing hamadryas baboons, geladas, snub-nosed monkeys, and a few other mammals such as elephants. In this type of system, there are at least three levels of social structure: the one-male unit (OMU), the band, and the troop or herd.
The OMU is the reproductive unit and consists of one “leader” male, sometimes a follower male, and several females; the band is the ecological unit that forages and sleeps together, and the troop or herd is a temporary aggregation at a sleeping site or foraging area. In hamadryas baboons, there is a fourth layer between the OMU and the band, the clan, which consists of OMUs and bachelor males linked by social bonds and possibly kinship among males. In geladas, bachelor males join together to form all-male groups. Reproduction in these societies is usually polygynous, and OMUs are always at risk of takeover by bachelor males, who may commit infanticide after taking over females with young infants.
It is important to note that the social organization of a species might not be immediately apparent from its social structure. For example, both geladas and hamadryas baboons are characterized by multiple layers of society, and their social structure is almost identical. However, the social organization of these two species could not be more different. In geladas, the cohesion of OMUs is maintained by philopatric females, as each OMU is a female kin group and these kin groups are taken over as entire units by males.
Bluewire Strategy – Primate Clan
In hamadryas, by contrast, a cohesion of OMUs is maintained by philopatric males who take over females one by one, often exchanging them with other males in their clans, and aggressively condition those females to remain in their OMU. Thus, hamadryas social organization includes strong male-female bonds (the glue that holds together an OMU) and strong male-male bonds (as males are philopatric and thus related to one another within bands and clans), whereas gelada social organization is characterized by strong female-female bonds (which hold together OMUs) but weak bonds between the sexes.
Moreover, one must be careful not to make assumptions about a species’ mating system simply upon observing its social system. For example, multi-male multi-female groups of gorillas may have an age-graded dominance structure in which only the oldest, highest-ranking (alpha) silverback male is allowed to copulate; in this case, the mating system is not polygynandrous (as one might expect in a multi-male group) but instead polygynous.
Another example can be found in guenons, which live in one-male groups. During the mating season, multi-male influxes occur in which outside males come into the group, copulate with the females, and then leave again. The mating system, in this case, is not polygynous, which one would expect, but polygynandrous. Finally, gibbons and siamangs were first thought to be monogamous, but then observations of extra-pair mating (i.e., copulations with individuals outside of the pair-bond) confirmed that they are not always monogamous but sometimes polygynous, polyandrous, or both.
Bluewire Strategy – Primate Clan
Smelly Family
