Before revision: The origin of multicellularity is a fundamental open question in biology. For URLanisms to evolve from an aggregate of URLanisms, cells with an identical genotype must first differentiate into several types.
After revision: As cells grow and divide under a given environment, they become crowded and resources are limited, as seen in bacterial biofilms and multicellular aggregates. These cells often show strong interactions through exchanging chemicals, as in quorum sensing, to achieve mutualism. Here, to achieve stable division of labor, three properties are required. First, isogenous cells differentiate into several types.