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Note: This article is illustrated by many images and videos taken in the �������� Embryology Course and features the research of Nicole King of University of California, Berkeley, who will become co-director of the �������� Physiology Course in 2019.

Billions of years ago, life crossed a threshold. Single cells started to band together, and a world of formless, unicellular life was on course to evolve into the riot of shapes and functions of multicellular life today, from ants to pear trees to people. It's a transition as momentous as any in the history of life, and until recently we had no idea how it happened.��

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