Chapter 9. Chapter 9: Evolution and Behavior

If a trait positively affects an individual’s relative reproductive success, the frequency of the allele for that trait is likely to increase in the population.

This is an example of an innate behavior that does not need to be learned. It is fixed, occurring in exactly the same pattern each time the behavior is started, and normally is not altered.

Behaviors that improved our ancestors’ reproductive success and survival are more likely to be easily learned.

The sight of a large, egg-like object acts as a stimulus to a goose and compels it to roll the object back into its nest, regardless of whether there are any smaller egg-like objects, including its own eggs, outside the nest. Only after the goose has rolled the larger egg-like object into its nest will it roll other, smaller egg-like objects into the nest.

Altruistic-appearing behaviors benefit the interests of closely related individuals, with whom an individual is more likely to share genes. It could be said that genes are acting in their own best interest.

The squirrel producing the alarm call is likely to be related to many of the other squirrels in the colony. When the squirrel sounds the alarm, it is helping to ensure the safety of others in the colony, many of whom share many of its genes. This is an example of inclusive fitness.

Any two of the following three conditions are correct: (a) Individuals must interact with others who could potentially be recipients or donors of altruistic-appearing behavior. (b) The benefit to the recipient of an altruistic-appearing behavior must be much greater than the cost to the donor. (c) Recipients of altruistic-appearing acts that do not reciprocate at a later time will be recognized and punished.

An example given in the text illustrates a maladaptive behavior. People often donate to a cause that benefits people who live in distant reaches of the planet—people the donor is unlikely to meet, so the behavior is unlikely to be reciprocated. The origins of this behavior go back to when humans lived in small communities in which altruistic-like behaviors were directed to other members of the community and were likely to be reciprocated. Humans of today live in much larger communities but behave as if they still lived in small ones.

No. Natural selection will favor behaviors that benefit the individual, not necessarily the group. In group selection, the reproductive fitness of individuals is decreased, and this type of selection cannot be sustained.

The female produces and retains the fertilized egg, and the offspring develops within her body. The male initially contributes only sperm. After birth of the offspring, the male may play a larger role—and in some cases, an equal role—in rearing young. Because offspring develop within the female, her energetic investment will initially always be larger than the male’s.

The sex that makes the greater reproductive investment is choosier about who it will mate with. Females make the greatest initial reproductive investment, but their overall reproductive investment may or may not be greater than that of the male. In cases where the male has a greater overall reproductive investment, it is in his best interest to ensure that his mate is carrying offspring with his genes and that these offspring grow to maturity. If the female makes the greater overall reproductive investment, she will try to find a mate that best ensures the success of her offspring. The degree of investment determines the risk: the greater the investment, the greater the potential risk.

Antler size indicates to the female the relative quality of the male as a potential mate.

In these mating systems, females are choosey about which males they mate with, choosing males with preferred physical traits or superior resources. Males of these systems must compete with other males for available females and may mate with multiple females. Males who cannot compete for mates, due to undesirable physical characteristics or poor access to resources, will mate with few if any females.

Monogamy: Two individuals mate and remain with each other. Polygamy: An individual has multiple mates; in polygyny, the male mates with multiple females; in polyandry, the female mates with multiple males.

The male moorhen probably provides the most care. The female makes a smaller reproductive investment; she must compete with other females for males and is physically larger and more aggressive than the males. Distinct differences between the sexes indicate sexual dimorphism, which is typically associated with polygamous mating systems.

An “honest signal” is one that cannot be faked. Both the animal making the signal and the animal receiving it have the same interests.