Jellyfish may seem like simple blobs but some have surprisingly sophisticated features, including eyes. These are often just light-sensitive pits but species like the root-arm medusa have complex ‘camera’ eyes, with a lens that focuses light onto a retina. Not only are these organs superficially similar to ours, they’re also constructed from the same genetic building blocks.

As you might imagine, growing an eye is a complicated business and involves a huge alliance of different genes, switching on and off in a coordinated way. But in humans and other animals, this alliance all comes under the control of a master gene called Pax-6. Pax-6 was discovered in 1994 by Walter Gehring, who also led the current Cladonema study. Faulty