Unlike most mammals, humans can see in a broad spectrum of colours. We share this trichromatic vision (able to distinguish reds, greens and blues) with the vast majority of Old World monkeys and Asian and African apes, but in South America, apart from the owl and howler monkeys, primates see things differently: some 40 per cent of females and all the males are dichromatic, or ‘colour blind’ (only able to distinguish greens and blues).
Colour-blindness may sound like a disadvantage, preventing individuals from being able to distinguish ripe red fruits in a green forest, for example. But it may also confer advantages, according to Andrew Smith from Anglia Ruskin University. "Being colour blind may actually enable the monkeys to focus more on shape and patterns," he says, "allowing them to spot camouflaged prey and predators more efficiently.”
Such physiological splitting within a species is unique among mammals. We still do not know, from an evolutionary perspective, why these species maintain both dichromatic and trichromatic characteristics.
Main image: Mico © Getty Images
