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UBC Theses and Dissertations

Evolutionary theory of cooperation and group life Barros Henriques, Gil Jorge

Abstract

Natural selection favors behaviors that increase an organism’s survival and reproduction. However, many organisms exhibit traits that benefit others at a cost to themselves, an apparent contradiction that Darwin called his “special difficulty”. The evolution of cooperation is an important biological question because it underlies group life and the construction of new levels of organization. For example, cells cooperate to make multicellular organisms and social insects as well as humans cooperate to establish large-scale societies. In this thesis, I attempt to increase our understanding of the evolution of cooperation and group life by developing four mathematical models. In Chapter 2, I study a question that dates back to Darwin: whether multilevel selection can be responsible for intergroup conflicts in human societies. Costly conflicts are collective action problems, and it is not clear what mechanisms could explain their prevalence. My model suggests one possible mechanism: the transmission of cultural traits between groups. Chapter 3 focuses on the interplay between the evolution of cooperation and environmental change. This model considers how cooperative interactions (public goods games), which evolve in response to changes in group size caused by environmental change, can either promote evolutionary rescue or, in some cases, lead to evolutionary suicide. In Chapter 4, I investigate the process of evolutionary branching (the diversification of a population into multiple strains), which can result from the evolution of cooperation between individuals. I show that, when multiple phenotypes experience evolutionary branching, the evolving phenotype distribution of the population can affect the direction of diversification. In the long-term, this may have important consequences for the evolution of division of labor. Finally, in Chapter 5, I consider how collectives of cooperating cells—including multicellular organisms and complex multi-species biofilms—reproduce to create new groups. I develop a multilevel selection model to investigate the consequences of various modes of reproduction, such as the production of single-cell gametes or vegetative fragmentation. Considered together, these four models expand our understanding of cooperation and group life.

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