A model of competition between unicellular and multicellular forms suggests that multicellularity can become ecologically stable without direct benefits, provided both forms use a varied environment in different ways.
Multicellularity has evolved repeatedly throughout Earth’s history. In particular, the current geologic eon — the Phanerozoic (539 million years ago (Ma) to the present) or ‘age of visible life’ — sustains an unprecedented abundance of multicellular forms. Geologists and biologists have long speculated on the selective advantages of multicellularity, particularly during its earliest stages: for example, multicellularity may have been selected for in our most recent unicellular ancestors — the direct ancestors of all animals — because this morphology helped them to escape predation. Such an advantage is a direct benefit, in which cells within groups outperform their single-celled counterparts under the same conditions. In the absence of direct benefits, the ancestral unicellular form is predicted to outcompete emerging multicellular forms, especially if there are costs to multicellularity, such as reduced access to nutrients. Writing in Nature Ecology & Evolution, Jorge et al. model how multicellularity can establish itself and persist without direct benefits, provided multicellular and unicellular forms use space differently… further reading