@article {Wahl010728, author = {Mary E. Wahl and Andrew W. Murray}, title = {Multicellularity makes cellular differentiation evolutionarily stable}, elocation-id = {010728}, year = {2014}, doi = {10.1101/010728}, publisher = {Cold Spring Harbor Laboratory}, abstract = {Multicellularity and cellular differentiation, two traits shared by all developing organisms, have evolved independently in many taxa and are often found together in extant species1. Differentiation, which we define as a permanent and heritable change in gene expression, produces somatic cells from a totipotent germ line. Though somatic cells may divide indefinitely, they cannot reproduce the complete organism and are thus effectively sterile on long timescales. How has differentiation evolved, repeatedly, despite the fitness costs of producing non-reproductive cells? The absence of extant unicellular differentiating species, as well as the persistence of undifferentiated multicellular groups among the volvocine algae2 and cyanobacteria3, have fueled speculation that multicellularity must arise before differentiation can evolve4-7. We propose that unicellular differentiating populations are intrinsically susceptible to invasion by non-differentiating mutants ({\textquotedblleft}cheats{\textquotedblright}), whose spread eventually drives differentiating lineages extinct. To directly compare organisms which differ only in the presence or absence of these traits, we engineered both multicellularity and cellular differentiation in budding yeast, including such essential features as irreversible conversion, reproductive division of labor, and clonal multicellularity. We find that non-differentiating mutants overtake unicellular populations but are outcompeted effectively by multicellular differentiating strains, suggesting that multicellularity evolved before differentiation.}, URL = {https://www.biorxiv.org/content/early/2014/10/25/010728}, eprint = {https://www.biorxiv.org/content/early/2014/10/25/010728.full.pdf}, journal = {bioRxiv} }