"Military planners in the Second World War noticed that color-blind soldiers were better at seeing through camouflage than were soldiers with normal vision... The superior pattern-finding abilities of dichromats may seem a peculiar but unimportant quirk of an unlucky mutation. Two facts suggest otherwise.
"First, the frequency of dichromatism in humans, two to eight percent of all males, is much higher than would be expected if the condition were a maladaptation. Such commonness suggests that evolution may, in some circumstances, smile on the condition.
"Second, our cousins the monkeys also have both dichromats and trichromats living together within the same species. Dichromats in these species make up half or more of the population, again suggesting that dichromatism is not just an accidental effect... New World monkeys generally live in cooperative groups, so it is to everyone's advantage to have both types of vision within the same group -- food can be found in all kinds of lighting conditions."
