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Chapter Summary

  1. We can study the evolution of social behavior using many of the same tools we use to study the evolution of other traits.
  2. Social behavior involves interactions that organisms have with others—most often, their conspecifics. In these interactions, the actions taken by one individual affect not only its own fitness, but also the fitnesses of those around it.
  3. Cooperation occurs when two or more individuals each receive a net benefit from their joint actions, even though individuals may pay a cost for interacting cooperatively.
  4. At least three different paths can lead to the evolution of cooperation: (1) kinship, (2) reciprocity, and (3) group selection. All three paths are susceptible to cheaters—those who receive the benefits of cooperation, but do not pay the costs.
  5. Evolutionary theory predicts that cooperation and altruism should be common among close relatives, because relatives are likely to share common genes that they have inherited from common ancestors—parents, grandparents, and so on. This idea has been formalized in inclusive fitness theory.
  6. Another path to cooperation is via reciprocal altruism in which individuals benefit from exchanging acts of altruism. One formal model for reciprocity is called the repeated prisoner’s dilemma game.
  7. A third path to cooperation may be via group selection, although this is a matter of heated debate among evolutionary biologists. The core concept underlying modern group selection models is that natural selection operates at two levels: within-group selection and between-group selection.
  8. Conflict can occur between unrelated individuals and, under certain conditions, between related individuals. Evolutionary biologists have developed and tested models predicting when and where such conflict should occur.
  9. Segregation distorters have been examined to study evolutionary conflict within genomes.
  10. Signals of one sort or another are involved in virtually all social interactions, whether they revolve around cooperation or conflict.
  11. In some cases, it is straightforward to understand how information sharing might evolve. If two individuals have entirely coincident interests, it is easy to see why both would benefit from communication.
  12. Despite some commonality of interests, signalers often have incentives to deceive. Evolutionary biologists have developed and tested many models of communication that address the incentive-to-cheat problem.
  13. Costly signaling theory suggests that if signals are costly and if, for one reason or another, dishonest signals cost more than honest signals, it may be worthwhile to communicate honestly and not to lie.
  14. Conventional signalsthat is, signals with meanings established by a convention, rather than signals with meanings that are intrinsically connected with their structure—can be honest if those who violate conventions are punished.