Chapter 11.  Kin Selection and Social Behavior

• The problem: social animals frequently behave in ways that reduce their individual fitness.  Why doesn't natural selection eliminate these behaviors?
• Altruism: self sacrificing behavior, action which benefits another at some cost to self.
• Alarm calls and cooperative rearing of young are examples.
• Field studies show that beneficiaries are usually kin of altruists.
• Could group selection be the solution to the problem?  Group selection occurs when there are fitness differences among groups.  If  groups that are composed of altruists survive longer than groups that are composed of selfish individuals, the presence of altruism would be explained.  Problem - individual selection will favor cheaters in the altruistic groups, transforming groups of altruists to groups of cheaters.
• Kin selection is better able to explain altruism than group selection.
• Inclusive fitness = direct fitness + indirect fitness (Hamilton)
• Hamilton's rule takes into account cost of act to altruist (C), benefit to beneficiary (B) and degree of relatedness (r) between altruist and beneficiary.  Natural selection favors altruism if Br - C > 0, or Br > C.
• r = coefficient of relatedness: 1/2 between parent and offspring, 1/2 between siblings, 1/4 between half-sibs, 1/8 between cousins, etc.
• Alarm calls in Belding's ground squirrels (Sierra Nevada).
• This behavior increases risk of predation to caller but reduces risk to others.
• The species is highly social.  Males disperse, females stay home, therefore there is a high degree of relatedness among females in a group.
• Females are more likely to call than males (Fig. 11.2), females are more likely to call when close kin are near (Fig. 11.3).
• Helping behavior in White-fronted Bee Eaters (African birds).
• Some first-year birds forgo reproduction, help others rear young (this reduces individual fitness but increases indirect fitness, hence increases inclusive fitness).
• Helpers are more likely to help relatives than non-relatives (Fig. 11.6).
• Fig. 11.7 shows that there is a real fitness gain due to helping.
• Reciprocal altruism can occur between non-related individuals, but this is more difficult to detect than altruism maintained by kin selection.
• Reciprocal altruism: individual behaves altruistically with the expectation that favor will be returned.
• Conditions for this trait to evolve:
• Cheaters are punished.
• Groups are stable.
• Individuals have good memories.
• Blood sharing in vampire bats - bats which have foraged successfully regurgitate blood for their less fortunate group members (Fig. 111.22).
• Sharing is more likely in bats that are related.
• Sharing will occur between roostmates that are not related.
• Hungry bats receive blood from bats they fed before.
• Evolutionary psychologists explain human emotions like gratitude, guilt and trust as evolving along with selection for reciprocal altruism. (Note that primate groups meet the conditions listed above for reciprocal altruism to evolve.)