How does multicellularity evolve? Scientists who study a family of green algae that includes unicellular Chlamydomonas and multicellular Volvox are beginning to find answers to this question.

Chlamydomonas reinhardtii is a unicellular freshwater green alga that is amenable to genetic studies and can be grown in the laboratory. It has a chloroplast, two flagella and an eye spot and is ...