Why Are Tigers Orange?
The colors of an animal serve lots of different purposes — for instance, to help them hide into surroundings and escape from being noticed by preys (猎物). For tigers, their ability to be invisible will just decide whether they catch dinner or go hungry.
As for humans, orange is a color used for items that need to stand out, like traffic lights and safety vests. That's because we have what's called trichromatic color vision, which differentiate three types of color: blue, green and red. But most other mammals, including dogs, horses and deer, have dichromatic (二色的) color vision for only two colors: blue and green. Humans who get information only of blue and green are considered color-blind, and can't distinguish between red and green colors.
Mammals like deer are the tiger's main prey, and their dichromatic vision means they don't see tigers as orange — they see them as green. That makes the tiger much harder to spot as it's prowling behind a bush or crouching in the grass. Although green tigers would probably be even harder to spot, evolution (进化) just doesn't work with the ingredients necessary to make green fur. The only recognizably green mammal is a sloth, and its fur isn't green in fact. That's an alga that grows in its fur.
There seems to be no evolutionary pressure, particularly for deer, which are the main prey of the tiger, to become trichromatic. That's probably because the tiger doesn't know it's orange either. So, the evolutionary race really doesn't exist for that color. It's just that the tiger has evolved over the sweep of evolution to have a coloring, a hiding system, which protects it very well in its jungle setting.
A. Actually, there are no green furry animals.
B. Orange fur makes tigers relatively easy to spot.
C. The same is likely true for dichromatic animals.
D. Then, why don't deer evolve the ability to see orange?
E. So, of all the colors they could be, why are tigers orange?
F. Colors of humans' eyes are quite similar to many other mammals'.
G. We share this style of vision with some mammals like apes and certain monkeys.
