Human vision like that of other primates has evolved in an arboreal environment. In the dense 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 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 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 of the darkness of night, we would be able to move easily in a strange shadowless world where objects glowed with varying degrees of intensity. But human eyes excel in other ways.

　　They are in fact remarkably discerning in color gradation. The color sensitivity of normal human vision is rarely surpassed even by sophisticated technical devices.

    考試須知：教育部研招通知  ♦2012考研時(shí)間安排   ♦考研院校專業(yè)報(bào)考指南

    準(zhǔn) 考 證：下載打印時(shí)間安排 ♦ 準(zhǔn)考證下載入口  ♦ 下載打印注意事項(xiàng)

    復(fù)習(xí)備考：考研政治時(shí)事匯總 ♦ 2012考研沖刺專題 ♦ 考研英語沖刺精華資料