Life’s Big Leaps: Critical Moments in Evolution

Scientists have begun to identify the symphony of biological triggers that powered the extraordinary expansion of the human brain.

The biologist Joan Strassmann discusses cooperation in social insects, how amoebas can teach us about competition, and why the definition of “organism” needs an overhaul.

A single genetic change and some clever geometry show how single-celled organisms can band together to form cooperative multicellular entities.

A newly discovered class of microbe could help to resolve one of the biggest and most controversial mysteries in evolution — how simple microbes transformed into the complex cells that produced animals, plants and fungi.