Seed magazine has a new article by evolutionary biologist PZ Myers on the deep common ancestry of different kinds of eyes in some cases. The article is “Eyeing the Evolutionary Past.” Prof. Myers points out that
“While eyes are common in larger animal species, about a third of all animal phyla lack eyes altogether; sea urchins do not bother with them, nor do many worms. Another third have eyes that look rudimentary to us; spots and patches and pits that can sense whether it’s night or day or whether a shadow is passing overhead, but that do not form any kind of image. The final third have true image-forming eyes that can capture a picture of what’s going on around them and pass that on to some kind of brain or nerve net. The phyla that have true eyes are a diverse subset of the multicellular animals, including jellyfish and sea anemones, molluscs, annelid worms, onychophora (velvet worms), arthropods, and us chordates, which is a strange distribution. It’s as if eyes popped up in scattered lineages interspersed with groups that lack them. For a long time, one of the hypotheses to explain all these eyes was that they evolved independently, multiple times within the animal kingdom.”
It’s a little creepy to me to think of sea urchins crawling on the ocean floor or jellyfish pulsing through the deeps without eyes to guide them. I know that some jellyfish have eyes. Others seem to lack them. But that last statement suggests that Prof. Myers is about to reveal a contrary discovery. First he explains a very fundamental difference between two kinds of eyes: ciliary and rhabdomeric. Read the article for a new insight into eyes and evolution.