Through the Language Glass

"Human color vision evolved independently from that of insects, birds, reptiles, and fish. We share our trichromatic vision with the apes and with Old World monkeys, but not with other mammals, and this implies that our color vision goes back about thirty to forty million years. Most mammals have dichromatic vision: they have only two types of cones, one with peak sensitivity in the blue-violet area and one with peak sensitivity in green (the middle-wave cone). It is thought that the primate trichromatic vision emerged from a dichromatic stage through a mutation that replicated a gene and split the original middle-wave (green) receptor into two adjacent ones, the new one being a little farther toward yellow. The position of the two new receptors was optimal for detecting yellowish fruit against a background of green foliage. Man's color vision seems to have been a coevolution with the development of bright fruits. As one scientist put it, "with only a little exaggeration, one could say that our trichromatic color vision is a device invented by certain fruiting trees in order to propagate themselves." In particular, it seems that our trichromatic color vision evolved together with a certain class of tropical trees that bear fruit too large to be taken by birds and that are yellow or orange when ripe. The tree offers a color signal that is visible to the monkey against the masking foliage of the forest, and in return the monkey either spits out the undamaged seed at a distance or defecates it together with fertilizer. In short, monkeys are to colored fruit what bees are to flowers." (Deutscher, Through the Language Glass, p. 247)