Evolution And History

56 CHAPTER 3 | Living Primates

of the protected preserve. These gorillas

spend close to 90 percent of their time

outside the national park, in and around

human-inhabited areas and farms. These

behavioral changes have many costs to

the gorillas, such as increased contact

with humans and human waste, conflict

with farmers that could result in injury,

increased exposure to hunting as these

areas are mostly open fields, and in-

creased risk of disease transmission.

Another effect on behavior may be an

artificial increase in group size. For ex-

ample, a group of some forty-four animals

now exist in the Virunga Mountains [along

the border of Rwanda, the Democratic

Republic of Congo, and Uganda] where

the average group size is usually ten

individuals. Furthermore, it is thought

that, due to their fear of humans, nonha-

bituated adult male gorillas that would

normally challenge other dominant males

are either deterred from presenting a

challenge or are less successful in their

challenge against habituated groups.

Perhaps the biggest threat to habitu-

ated great apes is disease. There are

over nineteen viruses and eighteen para-

sites that are known to infect both great

apes and humans. These diseases have

been responsible for be tween sixty-three

and eighty-seven ape deaths in habitu-

ated groups (both research and tourist

groups) in the Virungas, Bwindi, Mahale,

Tai, and Gombe.c As for the gorillas in

Bwindi, it has been shown that the prev-

alence of parasites such as Crytopspo-

ridium and Giardia are most prevalent

in habituated groups living near humans

along the border of the park.

In highlighting the costs of habitu-

ation in field primatology, as a great

ape primatologist, I know full well the

benefits that have come out of this

process. Weighing these costs and ben-

efits as a biological anthropologist, I

wonder if primatological field studies on

endangered great apes for the sake of

understanding humans is still a viable

option. Perhaps primatologists should

study apes only when it directly benefits

the welfare and conservation of the

study animals, rather than our interest

or curiosity in learning more ourselves.

Ethical considerations are crucial as the

numbers of great apes in the wild con-

tinue to dwindle. Habituation may not

be an ape’s salvation.

aInternational Union for Conservation of

Nature and Natural Resources (IUCN).

(2000).

bBlom, A., et al. (2001). A survey of the

apes in the Dzanga-Ndoki National Park,

Central African Republic. African Jour-

nal of Ecology 39 , 98–105.

cButynski, T. M. (2001). Africa’s great

apes. In B. Beck et al. (Eds.), Great apes

and humans: The ethics of co-existence

(pp. 3–56). Washington, DC: Smithso-

nian Institution Press.

CONTINUED

Primates as Mammals

Biologists classify humans within the primate order, a
subgroup of the class Mammalia. The other primates
include lemurs, lorises, tarsiers, monkeys, and apes.
Humans— together with chimpanzees, bonobos, goril-
las, orangutans, gibbons, and siamangs—form the hom-
inoids, colloquially known as apes, a superfamily within
the primate order. Biologically speaking, as hominoids,
humans are apes.
The primates are only one of several different kinds
of mammals, such as rodents, carnivores, and ungulates
(hoofed mammals). Primates, like other mammals, are in-
telligent animals, having more in the way of brains than
reptiles or other kinds of vertebrates. This increased brain
power, along with the mammalian pattern of growth and
development, forms the biological basis of the flexible
behavior patterns typical of mammals. In most species,
the young are born live, the egg being retained within
the womb of the female until the embryo achieves an ad-
vanced state of growth.
Once born, the young receive milk from their mother’s
mammary glands, the physical feature from which the class
Mammalia gets its name. During this period of infant de-
pendency, young mammals learn many of the things they
will need for survival as adults. Primates in general, and
apes in particular, have a very long period of infant and
childhood dependency in which the young learn the ways
of their social group. Thus, mammalian primate biology is
central to primate behavioral patterns.

Relative to other members of the animal kingdom,

mammals are highly active. This activity is made possible

by a relatively constant body temperature, an efficient re-

spiratory system featuring a separation between the nasal

and mouth cavities (allowing them to breathe while they

eat), a diaphragm to assist in drawing in and letting out

breath, and a four-chambered heart that prevents mixing

of oxygenated and deoxygenated blood.

Mammals possess a skeleton in which the limbs are

positioned beneath the body, rather than out at the sides.

This arrangement allows for direct support of the body

and easy flexible movement. The bones of the limbs

have joints constructed to permit growth in the young

while simultaneously providing strong, hard joint sur-

faces that will stand up to the stresses of sustained activ-

ity. Mammals stop growing when they reach adulthood,

while reptiles continue to grow throughout their lives.

Mammals and reptiles also differ in terms of their

teeth. Reptiles possess identical, pointed, peglike teeth

while mammals have teeth specialized for particular pur-

poses: incisors for nipping, gnawing, and cutting; canines

for ripping, tearing, killing, and fighting; premolars that

may either slice and tear or crush and grind (depending on

the kind of animal); and molars for crushing and grinding

(Figure 3.2). This enables mammals to eat a wide variety

of food—an advantage to them, since they require more

food than reptiles to sustain their high activity level. But

they pay a price: Reptiles have unlimited tooth replace-

ment throughout their lives, whereas mammals are limited

to two sets. The first set serves the immature animal and is