Is Poor Vision Useful?

There are lots of creatures alive today who have poor vision. They apparently find their vision useful. Blind cave fish show us that a creature which doesn't need its eyes, may lose them. So, a creature which has poor vision is using it.

The worst possible vision just tells a creature if it's light or dark. That might sound pretty useless, but lots of modern creatures (like scallops and Chlamydomonas) have that kind of vision. For example, there are sea dwellers who come to the surface at night. Or, a bottom-dweller could use sudden darkness as a warning that a shadow had been cast across it. It might indicate a good moment to retreat deeper into one's burrow.

For slightly better vision, you don't look in all directions. You point your eye. A sea creature which wanted to know which-way-to-the-surface would benefit from that, even with very poor pointing. Planaria learn the direction to the light, so that they can retreat into the deepest shadows.

With better pointing, you can tell which direction to the predator (or prey). That's useful if you need to know which escape route to use. Better pointing also makes it easier to not bump into things.

In short, information is useful to mobile creatures, and the more sophisticated the lifestyle, the more the players need to know. Bees need to see flowers, which means they need to see color. Predators need to know grabbing distances, so they get depth perception by having two or more eyes. Some sea creatures put their eyes out on long stalks: chameleons put them on turrets: grasshoppers and spiders put them all over the place.

Hawks and owls actually have better eyesight than humans. (They also see with four primary colors, rather than the three that humans use.) So, creatures that are alive today display a wide range of visual skills. All of them seem to benefit. Apparently "half an eye" is a wonderful thing.

Last modified: 10 February 1998

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