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McGill University
Biology (Sci)
BIOL 331
Greg Matlashewski

Why Do Animal Societies Evolve?  Social behaviour evolves when, by cooperating, conspecifics individuals can achieve higher rates of survival and reproduction than they would if they lived alone.  Social systems are dynamic; individuals repeatedly communicate with one another and adjust their relationship. Their relationships change regularly b/c costs and benefits experienced by individuals in a social system change with their age, sex, physiological condition, and status. Group living confers benefits but also imposes costs  It may improve hunting success or expand the range of food that can be captured.  Could also defend their prey and themselves from other carnivores, and they could tell one another about the locations of food and enemies.  Social behaviour has many costs: interfere with one another’s abilities, may inhibit one another’s attempts to produce or injure one another’s offspring, and increases exposure to diseases and parasites. Parental care can evolve into more complex social systems  Most widespread form of social system in an association of one or two parents with their immature, dependent offspring.  Many mammalian species have also evolved social systems based on extended families. In simple mammalian social systems, solitary females or male-female pairs care for their young. As the period of parental care increases, older offspring may still be present when the next generation is born. They often help rear their younger siblings.  In most social mammal species, female offspring remain in the group in which they were born, but males tend to leave or are driven out. Most helpers are females.  Caring for young involves tremendous costs for parents and helper. Altruism can evolve by contributing to an animal’s inclusive fitness  Natural selection can favour altruistic acts—behaviours that reduce the helper’s reproductive chances, but increase the fitness of the helped individual. Why?  An animal’s offspring contribute to its individual fitness.  By helping its relatives,
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