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Seeing colors

Ever wonder why some fruits are so colorful, like red raspberries and purple plums?

Scientists have long believed that the bright colors help animals find the fruits to eat them. By eating the fruits, animals help spread the plant’s seeds. When the plant’s seeds are spread, more of them can grow.

However, not many animals see fruit colors the same as we do. Humans have three cells in their eyes, called cones, which detect the colors red, green and blue. Most other mammals have only two cones.

That’s why hunters can wear bright orange. While orange will stand out in the woods and prairie to other hunters, deer and elk see orange as different shades of green. Birds have four cones, so they see everything humans can see and more.

Not all humans can see all colors. Some people are colorblind, which typically affects their ability to see greens and reds. Usually people are born colorblind.

Scientists at Duke University ran a study in the jungles of Uganda and Madagascar and found that “fruits that are mainly eaten by mammals, such as monkeys and apes,” reflect more green light, “whereas fruits dispersed by birds reflect more in the red — presumably because birds tend to rely more heavily on their keen color vision than many other animals, and reds are easier” to pick out in a green forest.

The scientists also found that fruits that reflect ultraviolet light, which humans can’t see, also have leaves that reflect UV light. This may be a way for the plants to avoid damage from the sun, just like we put sunscreen on to protect our skin from UV light.

Next the scientists plan to analyze other features of fruit such as odor, size or texture. "It may be that … scent is more important for luring animals whose sense of smell is keener than their sight," said German scientist Omer Nevo.

— Brett French,

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