In 2012, evolutionary biologist Megan Porter compared almost 900 opsins from different species, and confirmed that they share a single ancestor. That original opsin arose in one of the earliest animals and was so efficient at capturing light that evolution never conjured up a better alternative. Instead, the ancestral protein diversified into a wide family tree of opsins, which now underlie all vision. Porter draws that tree as a circle, with branches radiating outward from a single point. It looks like a giant eye.
