Romvy/Alamy
Why hasn’t evolution given us eyes in the back of our head or rear-view mirrors? (continued)
Eric Anderson, Wickford, Rhode Island, US
While the previous answers to this question were good, they missed something.
Many vertebrates have a third or “parietal” eye at the top of their head, including some lizards, frogs, salamanders and sharks. This eye doesn’t form images, but it is sensitive to light and dark. The parietal eye may even have developed from a more functional eye or pair of eyes that would have allowed true sight overhead or even to the rear.
“Some swallowtail butterflies have…
