Chapter 7: The Evolution of Cooperation

In macaques, vervets, and baboons, maternal support influences female dominance relationships and the outcome of aggressive encounters. Identify the characteristics of female dominance relationships in these species. Female dominance relationships are short-lived and change often. Ranking within matrilineages is mostly unpredictable. Maternal rank is transferred to offspring. Maternal kin occupy adjacent ranks in the dominance hierarchy.

*Correct* Maternal rank is transferred to offspring. "A mother's rank is transferred to her offspring, as shown in the graph" (Graph 7.17) Maternal kin occupy adjacent ranks in the dominance hierarchy. "All the members of one matrilineage rank above or below all members of other matrilineages." *NOT Correct* Female dominance relationships are short-lived and change often. "Female dominance relationships are usually stable and persist for months to years. This stability is likely due to the fact that females form alliances in support of their kin." Ranking within matrilineages is mostly unpredictable. "Maternal rankings are often predictable. Mothers usually outrank their daughters, and younger sisters outrank older sisters."

Which of the following are methods primates use to recognize their kin? Proximity Smell Patterns of Association Between Individuals Physical Similarity Vocal Cues Innate Recognition

*Correct* Proximity "The adults who spend the most time close by or touching infants and young are usually kin." Smell "After they give birth, females repeatedly sniff their newborns to learn their scent." Patterns of Association Between Individuals "Infants and young learn who their relatives are by observing patterns of association among group members. Those individuals that interact with their parents most often (like other brothers and sisters) are most often kin." Physical Similarity "Individuals that look physically similar are often most related. After they give birth, females repeatedly inspect newborns so they will be able to recognize their offspring." Vocal Cues "Because mothers only respond to the alarm calls of their own infants, they appear to be able to recognize their kin by the unique sound of their vocalizations." *NOT Correct* Innate Recognition "There is no evidence that infants are born knowing who their mothers are. Furthermore, there is no evidence that mothers would immediately be able to recognize their infants in a line-up."

To whom do mutualistic behaviors provide benefits? Neither the giver nor the recipient The recipient The giver

*Correct* The recipient The giver *NOT Correct* Neither the giver nor the recipient "Mutualistic behaviors provide benefits to both the giver and the recipient."

The theory that posits that natural selection can favor altruistic alleles if animals interact selectively with their genetic relatives is called __________ rule.

*Hamilton's* "In 1964, a young biologist named William D. Hamilton published a landmark paper stating that if altruists are more likely to interact with each other than chance suggests, then altruistic behaviors could be favored by natural selection. Thus, Hamilton's rule was born."

Which of the following statements about kin-relations in cooperatively breeding primates are true, and which are false? Mate competition is greater among related females. Cooperative breeding takes place more commonly among kin than among unrelated individuals. Some species can pass their sibling's genes (along with their own) to their offspring. This makes cooperative breeding more beneficial. Unrelated females help care for the young of the breeding female in order to prove that they will be a good parent. Sisters sometimes disperse together to form new groups, where one sibling acts as the dominant breeding female and the others help to raise young. In a cooperative breeding scenario, subordinate females are able to produce offspring as readily as dominant females.

*True* Cooperative breeding takes place more commonly among kin than among unrelated individuals. "Females are most likely to share breeding with their own daughters, less commonly with sisters, and rarely with unrelated females." Some species can pass their sibling's genes (along with their own) to their offspring. This makes cooperative breeding more beneficial. "Marmosets are known chimeras, or organisms that carry more than one genetically distinct population of cells derived from more than one zygote. They can pass genes related to all bodily tissues, including the gametes, of their siblings to their offspring." Sisters sometimes disperse together to form new groups, where one sibling acts as the dominant breeding female and the others help to raise young. "Dispersal can be very dangerous for a young female. Dispersing and forming new groups with same-sex siblings can reduce the potential of failure. This is why cooperative breeding situations sometimes arise among sisters." *False* Mate competition is greater among related females. "Actually, kinship seems to reduce the extent of competition among females to some degree." In a cooperative breeding scenario, subordinate females are able to produce offspring as readily as dominant females. "Cooperative breeding has its costs. When subordinate females produce offspring, the dominant female often kills them." Unrelated females help care for the young of the breeding female in order to prove that they will be a good parent. "Females rarely help care for the young of unrelated females." *Summary* "Kin-based relationships really do impact all aspects of group living, including breeding rights and reproductive success!"

Groups composed of kin (such as siblings) have a ________ chance of sharing a gene that codes for a particular behavior than populations composed of nonkin (not siblings). a. lesser b. greater

*b. greater* "If an individual has a gene that codes for a particular behavior (like being an alarm caller), then there is a 25% or 50% chance that the individual's siblings share that same gene. However, the same individual has a much lower chance of sharing the same gene with members of a population made up of nonkin. Thus, groups composed of kin have a greater chance of sharing a gene that codes for a particular behavior than populations of nonkin do."

According to Hamilton's rule, an act will be favored by selection if rb > c. Match the variables in Hamilton's rule to their definitions. Hamilton's Definitions: the average coefficient of relatedness between the actor and the recipients the fitness cost to the individual performing the behavior the sum of the fitness benefits to all individuals affected by the behavior

*r* the average coefficient of relatedness between the actor and the recipients "The coefficient of relatedness, r, measures the genetic relationship between interacting individuals. More precisely, r is the probability that two individuals will acquire the same allele through descent from a common ancestor." *b* the sum of the fitness benefits to all individuals affected by the behavior "The sum of benefits to all individuals affected by the act, b, is placed in a ratio of benefit:cost. This ratio scales with the degree of relatedness among individuals." *c* the fitness cost to the individual performing the behavior "The sum of cost to the individual performing the behavior, c, is placed in a ratio of benefit:cost. This ratio scales with the degree of relatedness among individuals." *Summary* "Now you can determine when an altruistic act is favored by natural selection and when it is not."

Place the following relationships in order from most closely genetically related to least closely genetically related. cousins parent-child half-siblings nonkin

1. Parent-Child 2. Half-Siblings 3. Cousins 4. Nonkin "You can correctly use kinship terms to reflect degrees of genetic relatedness! This is an important step in determining whether altruistic acts favor natural selection."

__________ behavior benefits others at a personal cost.

Altruistic "Remember this definition. It is central to our understanding of the evolution of cooperation."

Self-directed behaviors, like self-scratching, are a good behavioral index of __________. a. aggression b. stress c. trust d. affiliation

b. stress "When monkeys are nervous and anxious, rates of certain self-directed behaviors, such as scratching, increase. Thus, self-directed behaviors are a good behavioral index of stress."