Biomedical Engineering Reference
In-Depth Information
animals flee because they are being chased or are otherwise
avoiding a specific stimulus.
A second level of “Why?” is the function of the
response, i.e. the adaptive significance the response holds
for the animal. Adaptive significance is related to the
animal's ability to survive and produce offspring. Animals
may yield to higher-ranking group members because it is to
their advantage to “prevent” an aggressive encounter and
avoid being seriously injured. When a response is being
analyzed according to its adaptive significance, the
response should be characterized with respect to how it
influences an animal's fitness, i.e. its ability to survive and
reproduce. Although a particular behavioral act may
usually improve an individual's genetic fitness, that act may
actually not be adaptive in certain situations. The function
of a response differs from its immediate cause, and this
difference can lead to confusion if an act is being described
at two different levels: one level in terms of the act's
immediately preceding cause and the other in terms of its
future consequences with respect to fitness. “Function”
should never be confused with “intention”; no cognitive
awareness on the part of the animal is implied when
functions are discussed. For example, aggressive behavior
within a group of nonhuman primates can be interpreted as
either the result of introducing unfamiliar animals to the
same space or the establishment of a dominance hierarchy
that will better help control resource distribution within the
group. Why a particular animal dominates others in
contests for access to food may be influenced by both the
physical characteristics and social alliances of that indi-
vidual. To determine why dominant animals exist, one must
consider how the presence or absence of a dominance
hierarchy has adapted the species to its environment
(
Bernstein, 1981
).
Behavioral ontogeny explores how animals' responses
or interactions with other animals change or develop over
time. Beyond the physical development and learning
experiences that allow animals to respond using more
complex signals, behavioral ontogeny may also deal with
how animals are integrated into societies. For example, one
of the adaptations nonhuman primates exhibit is a longer
developmental period than that of other mammals of the
same size. An individual's position in the dominance
hierarchy may also be examined in terms of maturation and
the history of an animal's experience, such as the support of
a dominant or subordinate matriline. “Socialization”
comprises the lifelong process by which nonhuman
primates learn from and adapt
and which are conserved. It is thereby possible to infer
evolutionary changes in behavioral patterns and to develop
hypotheses about the selective pressures that have influ-
enced a species.
DEFINITION OF NONHUMAN PRIMATE
SOCIETIES
Social Structure vs. Social Organization
When studying the social behavior of nonhuman primates,
it is important not to confuse “social structure” with “social
organization.” Social structure concerns the demography of
a group of animals, the ratio of males to females and the
animals' reproductive patterns, territoriality, dietary limi-
tations, and other information. Note that the demography of
a group is not always equivalent to the breeding system.
Extra group copulations may be the norm, and individuals
that are not regular members of the group may participate
in breeding. So-called monogamous pairs may not breed
monogamously. Social organization, on the other hand,
deals with the interrelations between individuals within
a group. Obviously, social structure has a profound influ-
ence on the types of social organization a group exhibits.
Species that seem to spend a lot of time alone and that have
long inter-birth intervals, such as the orangutan, may not
rely on juvenile play groups to integrate younger animals
into the group.
Feeding patterns can also influence the extent and types
of social interactions experienced by a species. For
example, spider monkeys (Ateles) and howler monkeys
(Alouattinae) have very different troop cohesion patterns
that may be related to the types of food they eat. Spider
monkeys feed on fruit that is distributed in small, patchy
clumps; therefore, these monkeys must divide into small
groups that disperse to forage and come together later to
sleep. Conversely, howler monkeys move about in more
cohesive social groups, eating fruit, leaves, and flowers that
are abundant or in large clusters.
Social organizations can be described in terms of the
predictable patterns of interaction that occur within a group
of animals. When patterns of social interaction serve
specific functions, they are often described as “social roles”
(
Bernstein and Sharpe, 1966; Bramblett, 1973; Fairbanks
et al., 1978
). Many individuals may serve similar roles
(e.g. parental roles or group sentinel roles), and one indi-
vidual may serve multiple roles. The specific expression of
each role varies from species to species and reflects the
particular needs of the individuals and the social organi-
zation of the group. For example, paternal behavior is
expressed quite differently by marmoset males, who are
often monogamous, than by rhesus males, who live in
groups including many other adult males and infants.
Marmoset males routinely provide care for infants, carrying
their behavior
to the
constraints of their social environment.
Since evidence of actual behavior is scarce in the fossil
record, evolutionary questions are often approached by
comparing similar responses in existing species. In this
comparative method, morphological and behavioral data
are used to determine which species in a group are derived