MICHOD, RE: Cooperation and Conflict in the Evolution of Multicellularity

The organization of the living world is hierarchical; lower level units group together and cooperate to form higher levels of organization. Major landmarks in the diversification of life have involved transitions between these hierarchical levels. To be able to adapt to their environment, evolutionary units must satisfy Darwin’s conditions of heritability and variation in fitness. Using a multi-level selection framework, it is possible to understand how Darwin’s properties emerge at a new hierarchical level from the evolution of interactions in groups of lower level units. In this way, we may understand, in a general sense, the origin and maintenance of the biological hierarchy. Multicellular organisms likely originated as groups of cells. Cooperation among cells benefits the group, but may be costly to individual cells. We study conflict mediation, the process by which genetic modifiers evolve that enhance cooperation by altering the parameters of development or rules of formation of cell groups. We are particularly interested in the conditions under which these modifiers lead to a new higher-level unit of selection with increased cooperation among group members and heritable variation in fitness at the group level. By sculpting the fitness variation and opportunity for selection at the two levels, conflict modifiers create new functions at the organism level. An organism is more than a group of cooperating cells related by common descent; organisms require adaptations that regulate conflict and promote cooperation. Conflict leads, through the evolution of adaptations that reduce it, to greater individuality and harmony for the organism.