Hanschen, Erik R., Deborah E. Shelton, and Richard E. Michod. “Evolutionary transitions in individuality and recent models of multicellularity.” In Evolutionary transitions to multicellular life , pp. 165-188. Springer, Dordrecht, 2015.
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An evolutionary transition in individuality (ETI) is a fundamental shift in the unit of adaptation. ETIs occur through the evolution of groups of individuals into a new higher-level individual. The evolution of groups with cells specialized in somatic (viability) or reproductive functions has been proposed as a landmark of the unicellular to multicellular ETI. Several recent models of the evolution of multicellularity and cellular specialization have contributed insights on different aspects of this topic; however, these works are disconnected from each other and from the general framework of ETIs. While each of these works is valuable on its own, our interest in ETIs motivates an attempt to connect these models. We review the theory of ETIs along with these recent models with an eye towards better integrating insights from these models into the ETI framework. We consider how each model addresses key recurring topics, such as the importance of cooperation and conflict, life history trade-offs, multi-level selection, division of labor and the decoupling of fitness at the level of the group from the level of the cell. Finally, we identify a few areas in which conflicting views or unanswered questions remain, and we discuss modeling strategies that would be most suited for making further progress in understanding ETIs.