70 CHAPTER 3 | Living Primateshanging apparatus, though among apes only small, lithe
gibbons and talented gymnasts swing from branch to
branch in the pattern known as brachiation. At the op-
posite extreme are gorillas, which generally climb trees,
using their prehensile hands and feet to grip the trunk
and branches. While smaller gorillas may swing between
branches, in large individuals swinging is limited to lean-
ing outward while reaching for fruit and clasping a limb
for support. Still, most of their time is spent on the ground.
All apes except humans and their immediate ancestors
possess arms that are longer than their legs.
In moving on the ground, African apes “knuckle-walk”
on the backs of their hands, resting their weight on the
middle joints of the fingers. They stand erect when reach-
ing for fruit, looking over tall grass, or doing any activity
where they find an erect position advantageous. The semi-
erect position is natural in apes when on the ground be-
cause the curvature of their vertebral column places their
center of gravity, which is high in their bodies, in front of
their hip joint. Thus they are both “top heavy” and “front
heavy.” Though apes can walk on two legs, or bipedally,
for short distances, the structure of the ape pelvis is not
well suited to support the weight of the torso and limbs for
more than several minutes.
Gibbons and siamangs, the small apes that are native
to Southeast Asia and Malaya, have compact, slim bodies
with extraordinarily long arms compared to their short
legs and stand about 3 feet high. Although their usual form
of locomotion is brachiation, they can run erect, holding
their arms out for balance. Gibbon and siamang males and
females are similar in size, living in family groups of two
parents and offspring.
Orangutans, found in Borneo and Sumatra, are divided
into two distinct species. They are considerably taller than
gibbons and siamangs and are much heavier, with the bulk
characteristic of the great apes. In the closeness of the eyes
and facial prominence, an orangutan looks very human-
like. The people of Sumatra gave orangutans their name,
“person of the forest,” using the Malay term oran, which
means “person.” On the ground, orangutans walk with
their forelimbs in a fists-sideways or a palms-down posi-
tion. They are, however, more arboreal than the African
apes. Although sociable by nature, the orangutans of up-
land Borneo spend most of their time alone (except in the
case of females with young), as they have to forage over
a wide area to obtain sufficient food. By contrast, fruits
and insects are sufficiently abundant in the swamps of Su-
matra to sustain groups of adults and permit coordinated
group travel. Thus gregariousness is a function of habitat
productivity.^5While all apes or hominoids possess a suspensory hanging apparatus
that allows them to hang from the branches of the forest canopy, only
the gibbon is a master of brachiation—swinging from branch to branch.
The nonhuman hominoids can also walk bipedally for brief periods
of time when they need their arms free for carrying, but they cannot
sustain bipedal locomotion for more than 50 to 100 yards. Hominoid
anatomy is better adapted to knuckle-walking and hanging in the trees.© Gerard Lacz/Peter Arnold, Inc.
(^5) Normile, D. (1998). Habitat seen as playing larger role in shaping behav-
ior. Science 279 , 1454.
have documented primate social learning and innovation
in colonies of macaques in Japan. Similarly, field studies
of vervet monkeys in eastern and southern Africa have re-
vealed that these Old World monkeys possess sophisticated
communication abilities. In short, wherever primatologists
study primates they make fascinating new discoveries.
These discoveries contribute not only to the disciplines of
primatology, evolutionary biology, and ecology but also to
deepening our understanding of who we are as primates.
Chapter 4 includes more on the behavior of baboons and a
variety of other Old World monkey species.
Small and Great Apes
The apes of the hominoid superfamily are our closest
cousins in the animal world. Like us, apes are large, wide-
bodied primates with no tails. As described earlier, apes
possess a shoulder anatomy specialized for hanging sus-
pended below tree branches. All apes have this suspensory