Eyes have evolved in many different ways for the creatures that use them. From primitive cells with a sensitivity to light, they’ve branched out into the weird cluster eyes of the box jellyfish, the compound eyes of a fly, starfish eyes at the ends of their arms, and the sharp binocular vision of an eagle. Instead of looking at eyes as more advanced or less advanced, we should look at the way that animals actually use them.
As they evolved, so did their eyes. All the basic visual structures that exist today were present during the Cambrian, but they have been elaborated in an extraordinary variety of ways—again for specialized tasks. The male mayfly looks like it has a huge compound eye glued on top of another smaller one, devoted to scanning the skies for silhouettes of flying females. The aptly named four-eyed fish has divided its two camera eyes in two, so one half sits above the water’s surface and examines the sky while the other looks out for threats and prey below. The human eye is reasonably fast, adept at detecting contrast, and surpassed in resolution only by birds of prey—a good all-around eye for the most versatile animal of all.
While our eyes may be more advanced than, say, a flatworm's, the worm's eyes work pretty well for their own purposes. An article by Ed Yong at National Geographic looks at the many different ways eyes developed for different uses, with fascinating pictures. -via Metafilter
(Image credit: David Liittschwager/National Geographic)