狗是人类最好的朋友,千百年来,他们和人类相依相存。狗鼻子的灵敏度比人类高上一千倍，不幸的是，狗却分辨不出颜色。这是为什么呢？就让下面这篇文章来告诉你吧。

Man's best friend is colorblind, but, fortunately, his survival does not depend upon the ability to see colors. His keen sense of smell compensates¹ for his inability to see colors, and enables him to differentiate² between things.

Extensive scientific testing on dogs supports the conclusion that they live in a colorless world. The testing done primarily focussed on the dogs' responses to colors for food. Dogs could not tell the difference between one color, a signal for food, and other colors, that were not for food. Similar tests conducted on cats produced similar results, which led scientists to conclude that they, too, are colorblind and live in a gray world.

The inability of most animals to see colors, from an evolutionary³ standpoint, is quite simple to understand. Many colorblind animals have dull-colored coats, hunt for food in the dark of night, or graze in the dim twilight⁴ hours. Their other senses have developed to the point where the lack of color vision in no way impairs⁵ them. For them, life in a colorless world is neither a handicap, nor a threat to their survival.

The only animals, other than man, scientists can conclusively⁶ say have color vision are monkeys and apes. Both can be trained to open a colored door, behind which is food, and man can be trained to open a refrigerator door of any color!