Manus Patten

Major Reversions in Evolutionary Individuality

Life is organized hierarchically. We find genes in genomes, which are inside cells, which may compose multicellular individuals, which sometimes form eusocial groups. Each level of this organization emerged through major evolutionary transitions in individuality, where once-independent particles combined into unified collectives. Traditionally, the focus has been on how collectives cooperate to form new kinds of individuals. However, internal conflicts often attend the major transitions or eventually arise within these collectives, challenging their unity. We argue that these conflicts may promote the dissolution of collective individuality, a process we term a “major reversion.” This possibility has received little theoretical attention. Taking an agential perspective, we propose that collectives qualify as individuals to the extent that their constituent particles share aligned fitness interests. We introduce a mathematical framework that formalizes individuality in terms of two metrics: fitness unity, which quantifies the potential harm posed by internal conflicts, and trait unity, which captures differences in optimal strategies among particles. We explore how internal conflicts can lead to the breakdown of individuality and suggest ways to identify and empirically study such reversions. Ultimately, these conflicts may yield entities that are no longer individuals but rather compromises of competing sub-agents, marking a potential reversal in evolutionary transitions.