88 CHAPTER 4 | Primate Behavior
each of their young for about four to five years. After her
infant is weaned, she will come into estrus periodically,
until she becomes pregnant again.
Among primates, as among some other mammals, fe-
males generally give birth to one infant at a time. Natural
selection may have favored single births among primate
tree dwellers because the primate infant, which has a
highly developed grasping ability (the grasping reflex can
also be seen in human infants), must be transported about
by its mother, and more than one clinging infant would
interfere with movement in the trees. Only among the
smaller nocturnal prosimians, the primates closest to the
ancestral condition, are multiple births common. Among
the anthropoids, only the true marmoset, a kind of New
World monkey, has a pattern of habitual twinning. Other
species like humans will twin occasionally. In marmosets,
both parents share infant care, with fathers doing most of
the carrying.
Primates follow a pattern of bearing few young but de-
voting more time and effort to the care of each individual
offspring. Compared to other mammals such as mice,
which pass from birth to adulthood in a matter of weeks,
primates spend a great deal of time growing up. As a gen-
eral rule, the more closely related to humans the species is,
the longer the period of infant and childhood dependency
(Figure 4.2). For example, a lemur is dependent upon its
mother for only a few months after birth, while an ape is
dependent for four or five years. A chimpanzee infant can-
not survive if its mother dies before it reaches the age of
4 at the very least. During the juvenile period, young pri-
mates are still dependent on the larger social group rather
than on their mothers alone, using this period for learning
and refining a variety of behaviors. If a juvenile primate’s
mother dies, he or she may be adopted by an older male or
female member of the social group. Among bonobos, a ju-
venile who has lost his or her mother has very little social
standing in the group.
The long interval between births, particularly among
the apes, results in small population size. A female chim-
panzee, for example, does not reach sexual maturity until
about the age of 10, and once she produces her first live
offspring, there is a period of five or six years before she
will bear another. So, assuming that none of her offspring
die before adulthood, a female chimpanzee must survive
for at least twenty or twenty-one years just to maintain the
status quo in chimpanzee population. In fact, chimpanzee
infants and juveniles do die from time to time, and not
all females live full reproductive lives. This is one reason
why apes are far less abundant in the world today than are
monkeys.
A long slow period of growth and development, par-
ticularly among the hominoids, also provides opportu-
nities. Born without built-in responses dictating specific
behavior in complex situations, the young monkey or ape,
like the young human, learns how to strategically interactof evolution.^12 She points out that evolutionary theories
about sexual dimorphism and reproductive behaviors are
particularly susceptible to becoming “gendered.” That is,
the gender norms of the scientists can easily creep their
way (subconsciously, of course) into the theories they are
creating. Darwin’s era, despite the reign of Queen Victo-
ria, was firmly patriarchal, and male–male competition
prevailed in British society. Women of Darwin’s time were
denied basic rights like the right to vote and own property.
Inheritance laws favored first-born male heirs. Feminist
analyses such as Fedigan’s have contributed substantially
to the developing discipline of primatology.
Primate field studies have revealed that male–male
competition is just one of many factors playing a role in
primate reproduction. A broad range of social processes
contribute to reproductive success, with as much variation
as the numerous biological factors that contribute to body
size. For example, in baboons, which are a very sexually
dimorphic species, the female’s choice of mate is as im-
portant as male–male competition. Females frequently
choose to mate with lower-ranking males that show strong
male–female affiliative actions (tending to promote social
cohesion) and good parental behavior.^13
In orangutans, the avoidance of male–male competi-
tion has become biologically evident in the male pattern
of growth and development. Unlike gorillas that develop
their silver backs at the same time as they become sexually
active, orangutan males become sexually mature before
they develop the secondary sex characteristics that would
mark their adult status. Described in detail in this chap-
ter’s Biocultural Connection, this state of arrested devel-
opment allows these lower-ranking males to have sexual
alliances with females. Thus they optimize their personal
reproductive success while simultaneously avoiding the
stresses and costs of male–male competition.
Among baboons, paternal involvement has been
shown to have distinct advantages for offspring, including
more rapid growth in baboon infants if they receive atten-
tion from their fathers. In addition, adult males will also
intercede on their offspring’s behalf when the young ones
are involved in fights. In short, choosing a good mate can
optimize the reproductive success of female baboons.
Reproduction and Care of Young
The average adult female monkey or ape spends most of
her adult life either pregnant or nursing her young, times
at which she is not sexually receptive. Apes generally nurse
affiliative Tending to promote social cohesion.(^12) Fedigan, L. M. (1992). Primate paradigms: Sex roles and social bonds.
Chicago: University of Chicago Press.
(^13) Sapolsky, R. (2002). A primate’s memoir: Love, death, and baboons in East
Africa. New York: Vintage.