One reason to study green algae is because they can teach us something about the evolution of multicellularity. A number of related species in the Volvocalean family form a gradation of complexity between single-celled and simple multicellular organisms. The members of this family of algae differ in size, the number of cells they produce, and whether or not there is a split between germline and somatic cells. This split is thought to be central to understanding how a new level of individuality has evolved. — Calcott 2011, p. 39.