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the brain is typically 70% of adult size (
Napier and Napier,
1967
).
Schultz (1933)
also reports that the bregmatic
fontanel is typically closed at birth in rhesus macaques.
The cranium of the neonate is large in comparison to the
body and usually edentulous, but occasionally deciduous
incisors may be present. Both hands and feet are very well
developed and large in comparison to the limbs, and all four
extremities are used to cling to the mother's hair. All
primate neonates are dependent on their mothers at birth,
but the intensity and duration of this dependency vary from
species to species. The intensity of paternal participation in
early care varies widely among species, and in rare cases
such as Aotus includes very extensive paternal care.
The infant is characterized morphologically by the
eruption of the deciduous dentition and the concurrent
development of the face. Behaviorally, infancy is a period
of increased activity and exploration and ends at the time of
weaning. The age of independence varies widely from
species to species. Weaning does not occur until the motor
skills of the infant develop sufficiently for it to indepen-
dently negotiate the environment effectively. As a general
rule, arboreal species tend to have a longer period of
locomotor dependency. The rapidity, or slowness,
of weaning in a given species parallels its overall rate of
maturation. Species with short maturation times usually
have short infancy periods while those with long matura-
tion times usually have longer periods of marked depen-
dency. The term weanling characterizes the level of
development at the end of infancy.
The juvenile period spans the time between weaning
and puberty. The juvenile locomotes independent of its
mother, and, morphologically, the most notable increases
are in the growth of the limbs. During this time body
proportions change rapidly and many of the distinguishing
characteristics between New versus Old World monkeys
and apes become evident. The first permanent teeth erupt
and sexual dimorphism begins to appear in those species
where it is marked in adulthood. About this same time the
cranial sutures complete their fusion. The adolescent
growth spurt occurs late in the juvenile period, which ends
with puberty. In the literature, the juvenile period is
sometimes subdivided into two or more levels of maturity.
Sexual maturity and morphological maturity do not
correspond. Thus, adulthood is subdivided into various
phases with different morphological characteristics.
Young adulthood spans the time between sexual matu-
rity and morphological maturity and usually lasts for
several years. This stage is sometimes referred to as
subadult or late juvenile in the literature. In most primates,
sexual maturity occurs first, followed by skeletal maturity
and dental maturity, and finally full adult body weight is
achieved. New World primates, particularly the smaller
species, can be exceptions to this sequence in that dental
maturity is advanced and sexual maturity may be delayed.
TABLE 4.1
Gestation Periods of Higher Primates
Gestation
Period (Weeks)
Higher Primate
New World Monkeys
Saiiri boliviensis (
Watts, 1990a
)
22
Cebus (
Watts, 1990a
)
24
Ateles (
Hartwig, 1996
)
32
Old World Monkeys
Hanuman langurs (Semnopithecus
entellus)(
Ankel-Simons, 2007
)
26
Macaca mulatta (
Silk et al., 1993
)
24
Patas monkey (Erythrocebus patas)
(
Ankel-Simons, 2007
)
24
Apes
Lesser apes (
Ankel-Simons, 2007
)
30
Great apes
Bonobo (Pan paniscus)
(
Ankel-Simons, 2007
)
34
Orangutan (
Ankel-Simons, 2007
)
36
38
e
Gorilla (
Ankel-Simons, 2007
)
36
38
e
Chimpanzee (Pan troglodytes)
(
Ankel-Simons, 2007
)
38
Humans
Homo sapiens sapiens
38
Like prenatal development, postnatal development in
nonhuman primates closely resembles that of humans only
more rapid. Among species there is considerable variation
in the developmental timetables but not the overall
sequence of development. Certain aspects of growth and
development are also characterized by considerable intra-
specific variation due to sexual dimorphism of growth in
body size, timing of dental eruption, and sexual maturation.
At birth, the neonate is well developed, alert, and active.
Newborn body weight in rhesus macaques varies between
330
10% of nonpregnant
maternal body weight (
Schultz, 1933
), with females on
average weighing only slightly less (6 g) than males.
Average birth weight is 483 g (n
600 grams, approximately 6
e
e
709) (
Silk et al., 1993
);
it doubles by 5 months postnatal and quadruples by 15
months (
Schultz, 1933
). The head and limbs are relatively
large at birth, but grow more slowly than the trunk there-
after. In marked contrast to humans, where the brain is
typically only 25% of adult size at birth, most growth in
nonhuman primate brain size occurs prenatally and at birth
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