The next time you appreciate the beauty of a rainbow or the subtle hues of an impressionist masterpiece, you'll be taking advantage of the human brain's palette of an estimated 2.3 million colors. Why do people and many nonhuman primate species have the capability to distinguish so many hues? How did it benefit our ancestors to evolve this trait? After all, most mammals seem to do just fine with a less-discerning color vision. Dogs, cats, and many other familiar mammals, for example, can't discriminate between reds and greens.
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