Primate Social Organization 79For example, gibbons live in small nuclear family units
consisting of a pair of bonded adults and their offspring.
Orangutans tend to lead solitary existences, males and fe-
males coming together only to mate. Young orangutans
stay with their mothers until they reach adult status.
Chimps and bonobos live in large multi-male multi-
female groups. Among chimps and bonobos, the largest
social organizational unit is the community, composed
of fifty or more individuals who collectively inhabit
a large geographic area. Rarely, however, are all these
animals together at one time. Instead, they are usually
found ranging singly or in small subgroups consisting of
adult males together, females with their young, or males
and females together with young. In the course of their
travels, subgroups may join forces and forage together,
but sooner or later these subgroups break up again into
smaller units. When they do, some individuals split off
and others join, so that the new subunits may be dif-
ferent in their composition from the ones that initially
came together.did not expect our ancestors to possess tails or ischial
callosities—the hardened, nerveless buttock pads that al-
low baboons to sit for long periods of time. Tails are strictly
a monkey characteristic, not an ape one, and among the
hominoids, only gibbons and siamangs possess ischial
callosities. Instead, paleoanthropologists looking for evolu-
tionary information were trying to piece together examples
of convergence—of behaviors that might appear in large-
bodied, dimorphic primates living in large multi-male
multi-female groups in a savannah environment.
The upside of paleoanthropology’s “baboon hypoth-
esis” is that it led to many excellent long-term field stud-
ies of baboons that have yielded fascinating data on their
social organization, omnivorous diet, mating patterns and
other reproductive strategies, communication, and so
forth. As with most primate field studies, the evolutionary
questions remain in the background while the rich reper-
toire of primate behavior takes center stage.
Primate Social Organization
Primates are social animals, living and traveling in groups
that vary in size and composition from species to spe-
cies. Different environmental and biological factors
have been linked to the group’s size, and all the possible
organizational forms appear in various primate species.
ischial callosities Hardened, nerveless pads on the buttocks
that allow baboons and other primates to sit for long periods
of time.
community A unit of primate social organization composed
of fifty or more individuals who inhabit a large geographic area
together.© Paul van Gaalen/zeta/Corbis© Paul vanGaalen/zeta/CorbisThe behavior of baboons, a type of Old World monkey, has been particularly well studied. There are several
distinct species of baboon, each with their own social rules. In troops of hamadryas baboons (pictured), the
sacred baboons of ancient Egypt, each male has a harem of females over which he dominates. Female hama-
dryas baboons, if transferred to a troop of olive baboons, where females are less submissive, maintain the
passive behaviors learned in their original troop. But a female olive baboon placed in the hamadryas troop
quickly learns submissive behaviors in order to survive.