Interacting cells driving the evolution of multicellular life cycles

Evolution of complex multicellular life begun from the emergence of life cycle involving formation of cell clusters. Opportunity for cells to interact within clusters provided them an advantage over unicellular life forms. However, what kind of interactions may lead to the evolution of multicellular life cycles? Here, we combine evolutionary game theory with a model for the emergence of multicellular groups to investigate how cell interactions can influence reproduction modes during the early stages of the evolution of multicellularity. We identify evolutionary optimal life cycles as those which maximize the population growth rate. Among all interactions captured by two-player games, only eight life cycles were found to be evolutionarily optimal. Moreover, the vast majority of games promotes either of two classes of life cycles: (i) splitting into unicellular propagules or (ii) fragmentation into two offspring clusters of equal (or almost equal) size. Our findings indicate that the three most important characteristics, determining whether multicellular life cycles will evolve, are average performance of homogeneous groups, heterogeneous groups, and solitary cells.