29
The Earliest Known Vertebrates Had Four Eyes—and They Worked a Lot Like Ours Do, New Research Suggests
(www.smithsonianmag.com)
Eyes are one of the fastest organs to develop simply because small mutations in structure can convey enormous advantages. There's also a very clear through line between light sensitive patches, cup shaped light sensitive patches, pinhole eyes, and complex eyes. Every stage on the road to complex eyes gives some kind of distinct advantage.
Eyes remain simple for a long time only because complicated eyes weren't necessary for early creatures to be successful. The moment more complex eyes began to convey a competitive advantage, they developed in a flash, evolutionarily speaking.
