We Live In Two Distinct Visual Worlds
Have you ever wondered what it would be like to live on a planet where all the colors were different from what you're used to? Actually, you already have a lot of experience with two different worlds with two completely different color schemes. They're called night and day.
Eyes started out as simple light detectors. Only after a long period of evolution did our eyes develop rods, sensory receptors that we still use for night vision. Rods allow us to perceive images in black, white, and gray, but not in color. Later still came the development of cones. Blue cones were the first color cones to evolve from rods. Most species of New World monkeys have only rods and blue cones. About 30 million years ago, red and green cones evolved from the blue cones.
We share a visual system of those three cone colors with apes and Old World monkeys. The result is two different visual worlds. One is a daytime world of color, where you have to look directly at an object if you want to bring it into sharp focus. That's because the color cones are concentrated in the center of your retina, where an image is projected if it's in the middle of your visual field. The other world is black, white, and gray. In that colorless night-time world, objects are sharper if you look near them instead of at them. That's because the rods are concentrated away from the center of the retina, where images are projected if you look at them a little askance.
