Resolving the first steps to multicellularity.

Multicellular life has evolved many times, yet each origin requires free cells to integrate unselfishly into a higher-level individual. How can such transitions evolve? In a new paper, Herron and Michod investigate the recent origins of multicellularity in colonial algae. Their phylogenetic reconstructions provide a striking dissection of early steps, and altruistic traits are at the crux of it. Key evolutionary reversals are also revealed, where cellular selfishness might have thwarted multicellular integration.