Exploring Evolved Multicellular Life Histories in a Open-Ended Digital Evolution System

Abstract

Evolutionary transitions occur when previously-independent replicating entities unite to form more complex individuals. Such transitions have profoundly shaped natural evolutionary history and occur in two forms: fraternal transitions involve lower-level entities that are kin (e.g., transitions to multicellularity or to eusocial colonies), while egalitarian transitions involve unrelated individuals (e.g., the origins of mitochondria). The necessary conditions and evolutionary mechanisms for these transitions to arise continue to be fruitful targets of scientific interest. Here, we examine a range of fraternal transitions in populations of open-ended self-replicating computer programs. These digital cells were allowed to form and replicate kin groups by selectively adjoining or expelling daughter cells. The capability to recognize kin-group membership enabled preferential communication and cooperation between cells. We repeatedly observed group-level traits that are characteristic of a fraternal transition. These included reproductive division of labor, resource sharing within kin groups, resource investment in offspring groups, asymmetrical behaviors mediated by messaging, morphological patterning, and adaptive apoptosis. We report eight case studies from replicates where transitions occurred and explore the diverse range of adaptive evolved multicellular strategies.

Group-selection via aggregative propagule-formation enables cooperative multicellularity in an individual based, spatial model

“…It is known that in Dictyostelium discoideum there are many processes other than aggregation where extracellular signalization plays a role, like repulsion of each other, sensing the local cell concentration, the hunger and stress signals of the neighbours and estimation of the number of cells in the group [91]. We have intentionally ignored regulating mechanisms, like the paracrine signalization or other gene regulatory networks, studied by recent models [57,92], focusing on a minimal model to investigate the individual effects of group selection and sizedependent selection (predation). Likely such regulating mechanisms are evolved features that were not present when aggregative multicellular organisms have emerged.…”