During the several billions of years since life began on this planet, some organisms gained the capacity for multicellularity — the ability to make multiple cells and multiple cell types. How does multicellularity evolve?
Life is very good at reinventing itself over time, and one of its most important innovations has been multicellularity, the capacity to make multiple cells and cell types that carry out specialized functions. Without the evolution of multicellularity, our planet would be a very different place — a world without plants or animals of any kind, and of course without humans. Yet even though multicellular species have evolved independently in most major lineages of eukaryotic organisms — including not only those to which plants and animals belong, but also green algae, brown algae, red algae, ciliates, slime molds, and fungi — we know surprisingly little about how this evolution came about. Do certain properties predispose a unicellular lineage to make the leap to multicellularity? Are certain types of genes/gene families, or genetic mechanisms especially important for this sort of transition to occur? Does the evolution of multicellularity require big steps involving major increases in genome size and/or expansions in gene families, or even many new kinds of genes? Or might the transition to a multicellular form possibly take place in smaller steps, involving only subtle changes? Scientists who study a family of green algae that includes unicellular Chlamydomonas and multicellular Volvox are beginning to find answers to some of these questions.