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CHAPTER OUTLINE
33.1 Nature Versus Nurture: Genetic Influences
The “nature versus nurture” question asks to what degree our genes (nature) and environmental
influences (nurture) affect our behavior. Behavior encompasses any action that can be observed
and described.
Nest-Building Behavior in Lovebirds
Experiments with nest-building behavior lovebirds suggested this behavior has a genetic
basis.
Food Choice in Garter Snakes
Experiments with garter snakes showed that their food preference was genetically based.
Egg-Laying Behavior of Marine Snails
All of the egg-laying behavior of the marine snail Aplysia is controlled by egg-laying
hormones.
Twin Studies in Humans
Studies of separated twins show that they have similar food preferences and activity
patterns, and even select mates with similar characteristics, lending support to the
hypothesis that certain types of behavior are primarily influenced by nature (i.e., genes).
33.2 Nature Versus Nurture: Environmental Influences
Environmental influences also affect behavior. Learning is defined as a durable change in
behavior brought about by experience.
Learning in Birds
Laughing gull chicks’ begging behavior appears to be a fixed action pattern, but is, in
part, learned.
Imprinting
Imprinting is a simple form of learning that has a strong genetic component, as
first observed in birds when chicks, ducklings, and goslings followed the first
moving object they saw after hatching. The behavior develops only during a
certain sensitive period.
Social Interactions and Learning
White-crowned sparrows sing a species-specific song, but males of a particular
region have their own dialect. Social interactions assist learning in birds.
Associative Learning
A change in behavior that involves an association between two events is termed
associative learning.
Classical Conditioning
In classical conditioning, the presentation of two different types of stimuli at the
same time causes an animal to form an association between them. This suggests
that an organism can be trained or conditioned to associate a specific response to
a specific stimulus.
Operant Conditioning
During operant conditioning, a stimulus-response connection is strengthened.
33.3 Animal Communication
Some animals form a society in which members of species are organized in a cooperative
manner, extending beyond sexual and parental behavior Social behavior in animals requires that
they communicate with one another. Communication is a signal by a sender that influences the
behavior of a receiver.
Chemical Communication
Chemical signals have the advantage of being effective both night and day. The term
pheromone designates chemical signals in low concentration that are generally passed
between members of the same species.
Auditory Communication
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Auditory communication is faster than chemical communication and it is
effective both night and day. Language is the ultimate auditory communication.
Visual Communication
Visual signals are most often used by species that are active during the day.
Tactile Communication
Tactile communication occurs when one animal touches another.
33.4 Behaviors that Affect Fitness
Much of the behavior of organisms we observe today must have adaptive value.
Territoriality and Fitness
Animals often have a particular home range where they can be found during the course of
the day. Territoriality is actively defending a portion of their territory for their exclusive
use as a food source or as a mating area. Territoriality is more likely to occur during time
of reproduction.
Foraging for Food
Animals need to ingest food that will provide more energy than the effort
expended acquiring the food. The optimal foraging model states that it is
adaptive for foraging behavior and food choice to be as energetically efficient as
possible.
Reproductive Strategies and Fitness
Usually primates are polygamous and males monopolize multiple females. Because of
gestation and lactation females invest more in their offspring than males and are
concerned with a good food source. Tamarins are polyandrous and Gibbons are
monogamous.
Sexual Selection
Sexual selection is a form of natural selection that favors features that increase
an animal’s chances of mating, which lead to increased fitness. Sexual selection
often results in female choice and male competition because females have a
limited number of eggs and males produce a plentiful supply of sperm.
Mating in Humans
A study of human mating behavior shows that the concepts of female choice and male
competition apply to humans as well as to other animals.
Human Males Compete
Due to the high investment in having a child by women and the low contribution
of men, more men are available and have to compete with others for the privilege
of mating.
Females Choose
Females prefer a mate who can obtain (financial) resources and shows symmetry
in facial and body features, related to the “good genes” hypothesis.
Men Also Have a Choice
Men prefer youthfulness and attractiveness in females, signs that their partner can
provide them with children.
Societies and Fitness
The principles of evolutionary biology can be applied to the study of social behavior in
animals. Sociobiologists hypothesize that societies form when living in a society has a
greater reproductive benefit than reproductive cost.
Sociobiology and Human Culture
The culture of a human society involves a wide spectrum of customs. It is proposed that
human societies originated because of the need for cooperation, communication, and
tools in hunting large animals.
Altruism versus Self-Interest
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Altruism can be generally described as a self-sacrificing behavior for the good of another
member of the society. In general, altruistic behavior in animals is explained by the
concept of kin selection, which increases an individual’s inclusive fitness.
Reciprocal Altruism
In some bird species, offspring from a previous clutch of eggs may stay at the
nest to help parents rear the next batch of offspring, contributing to the survival
of its own kin and increases its chances of inheriting a parental territory.
Reciprocal altruism also occurs in animals that are not necessarily closely
related; it usually occurs in groups of animals that are mutually dependent.
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