The origin of consciousness was a world-defining event, comparable only with the origin of life itself. But the moment that consciousness emerged is buried deep in the evolutionary record and is hard to identify.

In this article, Simona Ginsburg and Eva Jablonka put forward their new theory about how and when consciousness evolved. They identify a unique marker of minimal consciousness that they believe drove the Cambrian explosion of biodiversity and answers the age-old question of which organisms are conscious.