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.

(A) The function of glsA appears to have been co-opted without change from an unknown function in the unicellular ancestor of Volvox, so that it is now part of a pathway (shaded green) that is ...