Some nocturnal animals usually have UV vision to distinguish shapes and colors better at twilight. As human ancestors gradually became diurnal, our vision evolved into the blue light spectrum. Those early beings still couldn't distinguish between red and green, however, until about 30 million years ago, when they developed "perfect trichromatic color vision," Shozo Yokoyama, a biology professor at Emory University and lead author of the new study, told Discovery News.
Even today, 8 percent of males can't distinguish between red and green "because they inherited new mutations from their ancestors that occurred relatively recently (evolutionarily speaking),"
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