This lecture introduces students to use of behavioral ecology to study social behavior (and thereby opens the door to the field of sociobiology, the topic of a follow-on course). The lecture starts with a discussion of conspicuous social behaviors seen in collective motion, as in starling murmurations, and discusses how the "selfish herd" hypothesis provides an explanation for these patterns based entirely on benefits to individuals (and not benefits to the group). This discussion motivates a description of the grid of social behaviors that mix costs and benefits to actors with costs and benefits to recipients, including altruism, spite, by-product mutualism, and selfishness. The bottom half of the lecture focuses on introducing inclusive fitness theory (kin selection) as an explanatory framework for understanding some forms of (apparent) altruism, where an individual pays an appreciable cost to perform an action that provides an appreciable benefit to a relative. This allows for introducing the Prisoner's Dilemma from game theory and using it to derive Hamilton's rule, which is a theoretical framework for predicting when benefits to relatives are strong enough to outweigh the costs to the individuals doing them. We then close by applying Hamilton's rule to a parental–investment problem considered by Trivers (first discussed in a prior lecture on parental care) that ends up predicting that offspring may evolve behaviors that lead to over-investment by parents relative to the investment strategy that is best for the reproductive success of the parents.
Topic highlights:
- explanations for collective motion behavior in herds
- taxonomy of social behaviors based on costs and benefits to actors and recipients
- inclusive fitness theory as a gene-centric framework for explaining helping behavior (apparent altruism between individuals)
- introduction to Hamilton's rule
- application of Hamilton's rule to an analysis of parent–offspring conflict in parental investment
Important terms: murmuration, selfish herd, domain of danger (or “Voronoi cell”), social exploitation, positive externalities, public good, by-product mutualism, negative externalities, common-pool resources (or open-access goods), Tragedy of the Commons, selfishness, altruism (or cooperation), spite (or altruistic punishment), Prisoner’s Dilemma, inclusive fitness theory (or kin selection), relatedness, direct fitness, indirect fitness, inclusive fitness, Hamilton’s rule, Generalized Hamilton’s rule
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