Size and complexity among multicellular organisms

The diversity of specialized cell types (‘complexity’) is estimated for a wide range of multicellular organisms. Complexity increases with size, independently of phylogeny. This is interpreted in economic terms as the consequence of a greater degree of cooperative division of labour within larger entities. The rate of increase of complexity with size is less in the case of a cooperative division of labour (cell types within bodies) than in the analogous case of a competitive division of labour (species within communities). This is atttributed to the inutility of single specialized cells whose goods must be shared among all the many cells of a large organism. Major groups of organisms differ in complexity at given size: animals are more complex than plants, and phaeophytes are simpler than either.