The best-selling novel The swarm captured the imagination of countless readers with the fascination of marine life. But it also showed how little we understand life in the depth of the ocean.

Scientists at the European Molecular Biology Laboratory [EMBL] and the Max Planck Institute [MPI] for Developmental Biology now explain the remarkable ability of marine zooplankton to swim towards light. Their study, published in the current issue of Nature, reveals how simple eyes of only two cells sense the direction of light and guide movement towards it. The key is a nerve that connects the eyes directly to the cells that mediate swimming. The research also provides new insights into what the first eyes in animal evolution might have looked like and what their function was.