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Answers to Thinking Critically Questions
Mader: Inquiry into Life, Twelfth Edition
Chapter 32
1. You are studying two populations of rats – one in New York and the other in
Florida. Adult New York rats seem to prefer Swiss cheese and Florida rats seems
to prefer cheddar. Design an experiment to determine the extent to which this
behavior may be genetically controlled versus environmentally influenced.
Explanation/Answer: One simple experiment would be to catch rats from New
York and Florida, breed them in the lab, and see if hand-raised newborns (without
their parents) have the same preferences as the adults in the field populations. If
offspring have no preference, an environmental or learned component would be
suggested. This could further be tested by rearing one offspring group (composed
of both New York and Florida rats) on one type of cheese and another offspring
group on another type of cheese. A cheese preference test could be conducted
later in life, and if rats that showed no preference at birth prefer the cheese they
were raised on later in life, an environmental (“nurture”) component is suggested.
A second experiment could involve cross-breeding New York and Florida rats,
and if offspring have no preference between Swiss or cheddar cheese relative to
pure New York bred or Florida bred rats, then a genetic component is supported.
2. Operant conditioning is often used to train animals, particularly pets. Describe an
example of operant conditioning and why you think it works.
Explanation/Answer: Operant conditioning involves rewarding a particular
behavior. It was originally described by B.F. Skinner, who performed
experiments where rats were trained to press a lever in order to receive a food
reward. Operant conditioning is commonly used to train dogs. When a dog
learns to sit or roll over or play dead, the owner often provides a “treat” when the
dog performs the commanded behavior. Pets can also be rewarded with praise or
affection. Nonetheless, operant conditioning is an associative behavior. Much of
animal behavior is driven by the need for food, and rewarding desirable behaviors
with food causes the animal to associate the behavior with food (or another
reward). Through time, this association results in the animal performing the
behavior on command.
3. Until about 15 years ago, it was long thought that most bird species were
monogamous – that is, at least within a breeding season, males and females paired
and mated only with each other. However, with advances in DNA technology,
researchers began to find out that offspring in a nest were often sired by males in
neighboring territories. When females mate with neighboring males, it is called
“extra pair copulation” or EPC. Why do you think EPC behavior might have
evolved in many bird species?
Explanation/Answer: For males, it is fairly straightforward since sperm are
energetically inexpensive. EPC behavior would tend to increase male fitness in
the absence of parental care (since the paired male would care for the offspring).
The EPC behavior would then be favored by natural selection for males of many
bird species. For females, it is a bit more complicated. Females may choose to
mate with neighboring males that have “good genes” – that is, perhaps they
appear more healthy (e.g., lower parasite load) than the male with which they
formed a pair bond. Or, perhaps they mate with neighboring males to have
“sexier sons.” Neighboring males may have sexually-selected characteristics,
such as bright plumage, that may make females have sexier sons (who would tend
to mate with more females than males with duller plumage). By choosing
“sexier” mates, females would have sexier sons, and those females would tend to
have more grandchildren, thereby increasing their inclusive fitness.
4. If altruistic behavior has usually evolved to improve the altruist’s inclusive fitness
by helping relatives, then why do you think humans perform altruistic acts for
completely unrelated individuals (e.g., jumping into a pool to save a drowning
person)?
Explanation/Answer: It is not exactly clear why altruistic behavior exists in
humans. In the context of culture, someone might save someone else’s life
because it makes them feel good to perform such an act. Perhaps people do it so
others would be indebted to them or for monetary gain. Perhaps some people
perform altruistic behavior so that their societal status would increase (e.g., to be a
“hero”) – this may afford them more opportunities (e.g., jobs) that may allow
them to improve their ability to obtain resources. Nonetheless, altruism in
humans is a complicated issue, but since we are a social species, there may be
some benefit in the context of living in a society.
5.
Various types of communication behavior have evolved so that males can attract
females for mating purposes. These may consist of loud calls, bright or
flamboyant mating displays, or the construction of elaborate structures. These
communication behaviors could also attract predators, which could result in the
death of the male, the female, or both. So, how could such behaviors evolve?
Explanation/Answer: The fitness benefit of elaborate mating behaviors must
outweigh the costs associated with attracting predators. Sexual selection by the
female, if strong, could cause the exaggeration of male traits, such as plumage
coloration. The fitness benefit could be counteracted by natural selection of
predators against males that are too bright because their predation risk is too high.