Humans tend to have a very narrow idea of what eyes can do and where they are located on an organism's body. But the natural word has a knack for defying our expectations: scallops have multiple eyes lining their fleshy mantles, sea stars have eyes at the ends of their arms, and some blind cave fish don't have eyes at all-just skin where their ancestors' eyes used to be. There's also incredible variation among more "traditional" eyes (i.e., those located on one's head). Some, like eagle eyes, can pick out small details from miles away. Others, like a flatworm's, can only differentiate between light and dark. Evolution has resulted in eyes that are meant to perceive vastly different stimuli, which is why we could stand to be a little more humble about what we think we "see."
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Key Facts In This Video
The most simple eyes, such as a flatworm's, differentiate between light and dark. 00:36
The development of eyes can be categorized into four stages, from simple to complex. 00:48
The most advanced eyes have high-resolution vision, and rely on lenses and corneas to sharpen their view of the world. 01:26