Mastering Concepts
35.1
1. What is ethology?
Ethology is the scientific study of animal behavior, especially in the natural environment.
2. Distinguish between the proximate and ultimate causes of an animal’s behavior.
A proximate cause of a behavior is the mechanism that makes it happen. An ultimate
cause of a behavior is the behavior’s survival value or reproductive value.
35.2
1. What is the traditional distinction between innate and learned behaviors?
Innate behaviors are instinctive behavior patterns that do not involve learning and tend to
be stereotypical in nature; traditionally they were viewed as under the control of “nature”
or genetic control. Learned behaviors are altered as an outcome of experiences;
traditionally they’ve been seen as under the influence of “nurture”.
2. Describe three examples of innate animal behaviors.
Reflexes are instantaneous, automatic responses to a stimulus. Taxis behaviors involve
movement toward or away from a stimulus. Fixed action patterns are triggered by an
environmental stimulus and go to completion even if the stimulus is withdrawn.
3. Explain the connection between the fru gene and courtship behavior in Drosophila.
The fru gene is required for development of the motor neurons that trigger the muscle
actions in the courtship dance leads to mating.
4. Name four types of learning.
Four types of learning are habituation, associative learning, imprinting, and observational
learning.
5. What are some examples of animal cognition?
Examples of animal cognition include reasoning, problem solving, tool use, the use of
sign language or symbols in communication, and speech.
6. How does song learning in the white-crowned sparrows illustrate the relationship
between genes and experience in determining an animal’s behavior?
A young sparrow that hears no song, or that hears the song of another species, will end up
performing an abnormal song. This observation indicates an interaction between
experience and a basic genetic template in the song-learning process.
35.3
1. What are three mechanisms by which animals find their way to a specific location?
Piloting is a mechanism that uses distant objects as a guide. Some animals can orient to
the sun, stars or magnetic fields. A few animals use true navigation.
2. Describe how optimal foraging theory explains an animal’s foraging decisions.
Optimal foraging theory states that animals will maximize their energy returns for each
unit of time spent foraging. An animal’s optimal strategy reflects a trade-off between the
calories in the food versus time spent searching for, obtaining, and handling the food. .
3. What are some behaviors that help animals avoid predation?
Distraction displays that divert a predator from a nest or den, mobbing by groups, and
alarm calls are all examples of predator avoidance behaviors.
35.4
1. List three functions of animal courtship rituals.
Courtship displays ensure that the male and female are of the same species. They also
coordinate physiological and hormonal responses between the pair. Finally courtship
displays allow each to gauge the suitability of the other as a mate.
2. Describe examples of sexual selection between males and between males and females.
Intrasexual selection occurs when males compete with one another for exclusive access to
females. Examples of traits that reflect intrasexual selection include the size of the
proboscis in elephant seals and the size of antlers in deer. Intersexual selection occurs
when females choose among multiple males. Examples of traits that reflect intersexual
selection include a male peacock’s tail and the color of a rooster’s comb.
3. What is the relationship between sexual dimorphism and mating systems?
Species that are polygamous typically display sexual dimorphic characteristics. Species
that are monogamous are typically not sexually dimorphic.
4. Explain how confidence of paternity influences the degree of parental care by a male.
The more confident a male can be that offspring are his, the more likely it is that the
energy he spends on parental care will enhance his own reproductive fitness. Therefore,
males with high confidence of paternity tend to invest more time and care into the young.
5. How do observations of reproductive behavior in nonhuman animals enable
researchers to make predictions about humans?
Women invest more in rearing offspring than do men; therefore, one prediction is that
women should be choosier than men in selecting mates. In addition, in species with
sexual dimorphism, monogamy is not the rule. Humans show sexually dimorphic
characteristics, and in fact researchers have found that 85% of populations have some
degree of polygyny. Third, in nonhuman animals, males invest more in offspring when
they have greater confidence that the offspring are theirs. In human males, this
observation translates to forms of mate guarding.
35.5
1. What are some costs and benefits of group living?
Costs include higher competition for food and mates; diseases also spread easily within a
group. A group may also be more visible to predators than individual organisms. Benefits
include enhanced protection from cold and predators.
2. Explain the roles of dominance hierarchies and territoriality in animal societies.
Dominance hierarchies assign mating rank within a group, reducing competition for
mates. Territoriality provides individuals or groups of animals with exclusive access to
resources.
3. Define altruism and explain why evolution should select against it.
Altruism is one individual helping another with no benefit to itself. Because it brings no
benefit to the helper, the helper has wasted energy and should be at a competitive
disadvantage.
4. How do kin selection and reciprocal altruism explain some examples of cooperation
among animals?
In kin selection, an animal increases the fitness of its relatives at its own expense.
Although the animal’s own fitness is reduced, its family’s genes overall are passed on. In
reciprocal altruism, one animal helps another but may be later helped itself.
5. What is eusociality?
Eusociality is a social division of labor, especially concerning mating. Typical traits of
eusocial animals include cooperative care of young, the presence of sterile castes that
help care for breeding animals, and the care of young by older siblings.
35.6
1. How did the researchers test the hypothesis that the number of ADH receptors in the
brain’s reward area influences pair-bonding?
They injected a virus containing a gene encoding the ADH receptor into the reward area
in the brains of male voles. Controls received the same gene in a different brain region or
received a different gene in the same region as the experimental animals. The animals
then participated in partner-preference tests to determine which animals formed pair
bonds the fastest.
2. Could the researchers have drawn the same conclusions if they had omitted one of the
control groups? Why or why not?
No, because they would not know if the location of the injection caused the effect if they
had not included animals in which the virus was injected into another location. Second,
they would not know if the ADH gene caused the effect in the injected area if they had
not included a “non-ADH” control injection into the same area.
Write It Out
1. Differentiate between the proximate and ultimate causes of a particular behavior.
Scientists who study proximate causes of behavior investigate the physiological basis of
behaviors (“how” questions). Scientists who study ultimate causes of behavior focus on
the evolutionary explanations for behaviors (“why” questions)
2. People tend to see what they expect to see. How can ethologists prevent themselves
from falling into this trap when observing an animal’s behavior?
When observing animal behavior, ethologists can avoid falling into the trap of “seeing
what they expect to see” by having other observers present who are not aware of the
expectation of the ethologist and have them make independent observations of the
animals’ behavior.
3. How is a taxis different from a reflex? How are they similar?
Taxes are movements towards or away from an external stimulus, whereas a reflex is an
instantaneous, automatic response to a stimulus. They are similar in that both are innate.
4. In what way is a taxis similar to and different from a tropism in a plant (see chapter
23)?
In both instances the organism is directing its movement toward or away from a stimulus.
A taxis is based on the movement of an entire animal; a tropism is based on differential
growth in a plant.
5. Give an example of a fixed action pattern.
Many answers are possible, but one example of a fixed action pattern is the behavior of
the praying mantis when it catches and eats its prey. This behavior is consistent in adult
mantids as well as in newborns.
6. Explain how biologists identify genes controlling behavior in a fruit fly. Why might it
be difficult to identify similar genes in humans?
Biologists can use chemicals or radiation to cause mutations in fruit fly genes and then
observe the behavior of the resulting mutant organisms. Although it is possible to search
the human genome for genes that are homologous to fruit fly genes, it is unethical to
intentionally mutate genes in humans and then observe any changes in the person’s
behavior.
7. How is observational learning different from imprinting?
Imprinting involves a short time window and does not require reinforcement.
Observational learning can occur at any time in an animal’s life and requires
reinforcement as the behavior is observed repeatedly and practiced.
8. Once accustomed to captivity, praying mantids tend to stop making the startle response
when their caregivers come near. Given what you now know about animal behavior,
construct a hypothesis to explain this change. How would you test your hypothesis?
Praying mantids in captivity may become habituated to the presence of their caregivers
but not other humans. One way to test this hypothesis would be to divide captive mantids
into two groups; half could be approached by a familiar handler, and half would be
approached by a stranger. The same people could also approach recently caught mantids.
The responses of the animals would indicate whether captive mantids become habituated
to their handlers or to people in general.
9. Male thynnine wasps approach and attempt to mate with female wasps that release
pheromones. Some orchid flowers, however, emit a chemical that mimics the female
wasp’s pheromone so convincingly that male wasps will attempt to copulate with the
flower. Once a male visits a flower, however, he learns to avoid the flower in the future.
How does this example illustrate the interaction between innate and learned behaviors?
What type of learning has occurred in the male?
The wasps exhibit associative learning, as they experience the incorrect result of the
flower’s cue and do not repeat the behavior.
10. How is it incorrect to refer to a gene “for” alcoholism?
A gene encodes a protein, not a behavior. Even if a gene predisposes a person to
alcoholism, other environmental factors may determine whether the individual would
actually become an alcoholic.
11. Suppose an American couple moves to Australia and raises all of their children in
their new country. The children all speak English with an Australian accent. What does
this mean about the influence of environment on a person’s accent? Does this mean that
speech does not have a genetic component?
The environment determines how a person forms his or her words, but this does not mean
that speech does not have a genetic component. Genes control the development of the
bones, muscles, nerves, and brain structures that physically enable a person to speak.
12. How is the idea of “nature versus nurture” outdated? How might an investigator use
studies of identical twins raised apart to sort out the contribution of genes and
environment to a particular behavior?
Nature versus nurture implies that some behaviors are totally under genetic influence
with no learned components, and other behaviors depend entirely on the environment and
experiences. In fact, all behaviors have at least some genetic and some environmental
influence. By studying identical twins that have had no connection since birth and are in
different environments, researchers can look for behaviors that have a strong genetic
component and those that are modified based on learning and experience.
13. For three weeks in October 2002, two snipers terrorized people in the Washington,
D.C., area. Bystanders observed that pedestrians waiting to cross the street would stay
under cover until a group formed in the crosswalk. They would then dash out and join the
group to cross. Explain this observation with respect to the selfish herd hypothesis.
The selfish herd hypothesis predicts that animals will group tightly together, increasing
each individual’s chance of survival as others may become the predator’s target. This
appears to be the same behavior the pedestrians displayed in response to the sniper.
14. European cuckoos and American cowbirds are “brood parasites” that lay their eggs in
the nests of other birds. The chicks are generally raised by “adoptive parents” whose own
chicks receive less nourishment and often are killed by the larger intruders. What kinds of
behaviors does natural selection favor in the cuckoo and cowbird chicks? In the adoptive
parents?
In cuckoo and cowbird chicks, natural selection favors aggressive behavior that
eliminates rivals from the nest. In adoptive parents, natural selection favors well-hidden
nests, denying access to the nest by adult cuckoos and cowbirds, the production of
multiple broods consisting of many offspring, and the ability to discriminate between
their own offspring and the cuckoo or cowbird chicks.
15. Think of an example of a sexually dimorphic species other than those mentioned in
this chapter. How might sexual selection have led to this sexual dimorphism?
Species examples will vary, but may include elk, lions, walruses, mandrills, gorillas, and
mallard ducks. If females choose their mates based on larger body size, brighter
coloration, or some other visible trait, then those males with genes encoding the extreme
trait are more likely to pass on their genetic information to the next generation. Over
many generations, the sexes will become sexually dimorphic.
16. Use the Internet to investigate the mating behaviors of corals, sea horses,
chimpanzees, and salmon. Arrange these species in order from lowest to highest
confidence of paternity. Does the degree of paternal care follow the same pattern?
Explain your answer.
Confidence: coral (eggs often fertilized while free floating), chimpanzees (females mate
opportunistically with many males), salmon (male winning competition fertilizes a
female’s eggs several times, female generally mates with one male only), sea horses
(female implants eggs into male pouch and he carries them through gestation). The
degree of care follows the same pattern, indicating that natural selection favors extensive
paternal care only if the male has high confidence of paternity.
17. Read section 31.5 to learn about a male spider that allows his mate to eat his body
during copulation. How does this unusual behavior improve the male’s confidence of
paternity?
Because the male allows the female to eat his body, the female copulates with him for a
longer period, even as he is dying, and a greater percentage of her eggs are fertilized by
his sperm.
18. What are some of the costs and benefiting of associating with a group? Can you think
of some costs and benefits not mentioned in this chapter?
Advantages include greater protection from cold or predators, and cooperation in finding
food. Disadvantages include easier detection by predators detect large groups, increased
competition for some resources, and easier spread of disease. Additional benefits might
include multiple models for learned behaviors and the availability of extra helpers in
parental care. Additional costs might be increased competition for mates, including the
possibility of not mating at all.
19. Are humans solitary or social animals? Explain your answer.
Although many humans enjoy spending time alone, we are by and large social animals.
From the beginning of our lives, we rely on interactions with other people to develop
language skills, appropriate emotional responses, and many other aspects of mental
health. In addition, humans form units of cooperation, starting with the family unit.
Families are arranged into communities, and many individuals work to the benefit of the
entire community.
20. At home, you are usually a sound sleeper, but when you travel, you toss and turn and
get little sleep. Give a behavioral explanation for this observation.
A person becomes habituated to the familiar sounds, temperature, bed, and other stimuli
in his or her home. The unfamiliar stimuli away from home cause the nervous system to
be more alert, which makes it more difficult to sleep.
21. How is it advantageous for a species to have a fixed action pattern that controls
courtship or mating behavior?
Fixed action patterns occur in essentially the same way each time they are performed.
Any variation from the routine could lead to a loss of mating opportunities, which would
lead to lower reproductive success.
22. What is kin selection, and how can it explain some types of altruistic behavior? Can
you think of examples of true altruism in humans or nonhuman animals?
Kin selection sacrifices an individual’s genes for the sake of the genes it shares with
related individuals. True altruism requires that an animal would deny itself or put itself at
great risk to allow nonrelatives to survive and reproduce. Such behaviors are extremely
uncommon, even among humans, although some anonymous acts of philanthropy or
heroism may qualify.
23. In the 1930s, the population geneticist J. B. S. Haldane famously said, “I would lay
down my life for two brothers or eight cousins.” What was he talking about?
You share half your genes with each of your siblings, so two brothers would, on average,
share 100% of your genes. You share 1/8 of your genes with your cousins, so the eight
cousins would also total 100%.
Pull it Together
1. Compare and contrast innate and learned behaviors.
Innate behaviors and learned behaviors both contribute to the blend of behaviors
exhibited by an animal. Innate behaviors exist in the animal no matter what
environmental conditions it is raised with. Learned behaviors develop as a result of
interaction with the environment.
2. Add foraging, habituation, kin selection, fixed action pattern, eusocial, inclusive
fitness, imprinting, and reciprocal altruism to this concept map.
Foraging could be included as a behavior required for survival. Habituation and
imprinting are forms of learning. Kin selection, inclusive fitness, and reciprocal altruism
may explain some forms of cooperation. A fixed action pattern is a type of innate
behavior. Eusocial animals exhibit many social interactions.
3. Describe some of the behaviors that help animals avoid predation.
Many behaviors can help animals avoid predation. Examples include: having a quick
startle response; having keen senses of hearing, sight, and smell; having the ability to sit
very still for long periods; finding or making protective shelters; and minimizing scent
cues that might attract predators.