Evolution of colour vision

The evolution of color vision causes light to be seen according to its wavelength. This has obvious advantages, especially it helps animals find food.

The color vision of many herbivores allows them to see fruit or (immature) leaves which are good to eat. In hummingbirds, particular flowers are often recognized by color. Predators also use color vision to help them find their prey.

All this applies mainly to animals in the daytime. On the other hand, nocturnal mammals have much less-developed color vision. For them, space on the retina is better used with more rods since rods collect light better. Color differences are much less visible in the dark.

Arthropods

Apart from vertebrates,^[1] the only land animals to have color vision are arthropods.^[2] So insects and spiders have quite good color vision. Aquatic arthropods such as crustacea also have color vision. As with vertebrates, the details differ, but the molecules which do the work – the opsins – are very similar.

Vertebrates

Four photopigment opsins exist in teleost fish, reptiles and birds.^[3] This suggests that the common ancestor of tetrapods and amniotes (~360 million years ago) had full color vision:

"rods and four spectral classes of cone each [have] one of the five visual pigment families. The complement of four spectrally distinct cone classes gives these species the potential for tetrachromatic color vision".^[4][5]

Mammals

In contrast, mammals lost much of their color vision capability during the long period in the Mesozoic when they lived as nocturnal animals.^[4][6]

"...two cone opsin gene families appear in contemporary eutherian mammals and, with the exception of some primates, none of these animals derive more than a single photopigment type from each of their two gene families".^[5]

Many primates do live as daytime animals, and one group – the Old World monkeys – has trichromatic vision.^[7] The anthropoid apes and humans are descended from this group of monkeys,^[8] and also have good color vision. So it comes about that most monkeys and humans have good color vision, but most other eutherian mammals do not: they have only two opsins, and so they are bichromatic.^[9]

This has many consequences. For example, most deer cannot see red or orange. Thus they do not see the orange color of tigers. But monkeys do, because primates have one more opsin than other mammals. A film by David Attenborough illustrates this well.^[10]

UV light

Ultraviolet light plays a part in color perception in many animals, especially insects.

Color vision, with UV discrimination, is present in many arthropods—the only terrestrial animals besides the vertebrates to have this trait.^[2]

Birds, turtles, lizards, many fish and some rodents have UV receptors in their retinas.^[11] These animals can see the UV patterns found on flowers and other wildlife that are invisible to the human eye.^[12][13]