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Human vision like that of other primates has evolved in an arboreal environment. In the densecomplex world of a tropical forest, it is more important to see well than to develop an acutesense of smell. In the course of evolution members of the primate line have acquired large eyes while the snout has shrunk to give the eye an unimpeded view.
Of mammals only humans and some primates enjoy color vision. The red flag is black to the bull. Horses live in a monochrome world.Light visible to human eyes however occupies only a very narrow band in the whole electromagnetic spectrum. Ultraviolet rays are invisible to humans though ants and honeybees are sensitive to them. Humans have no direct perception of infrared rays unlike the rattlesnake which has receptors tuned into wavelengths longer than 0.7 micron. The world would look eerily different if human eyes were sensitive to infrared radiation. Then instead