新东方背诵文选 L46.Vision by

（单词翻译）

Human vision like that of other primates² has evolved in an arboreal³ environment. In the dense⁴ complex world of a tropical forest, it is more important to see well that to develop an acute sense of smell. In the course of evolution members of the primate¹ 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 spectrum⁵. Ultraviolet rays are invisible to humans though ants and honeybees are sensitive to them. Humans though ants and honeybees are sensitive to them. Humans have no direct perception of infrared⁶ rays unlike the rattlesnake which has receptors tuned⁷ into wavelengths⁸ longer than 0.7 micron. The world would look eerily⁹ different if human eyes were sensitive to infrared radiation. Then instead of the darkness of night, we would be able to move easily in a strange shadowless world where objects glowed with varying degrees of intensity¹⁰. But human eyes excel in other ways. They are in fact remarkably¹¹ discerning in color gradation. The color sensitivity of normal human vision is rarely surpassed even by sophisticated technical devices.