Color vision, a proximate adaptation of the vision

sensory modality Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light ...

, allows for the discrimination of light based on its

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...

components.

Improved detection sensitivity

The evolutionary process of switching from a single

photopigment Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore moiety of photosensitive chromoproteins, such as the pigments involved in photosynthesis and pho ...

to two different pigments would have provided early ancestors with a sensitivity advantage in two ways. In one way, adding a new pigment would allow them to see a wider range of the electromagnetic spectrum. Secondly, new random connections would create wavelength opponency and the new wavelength opponent neurons would be much more sensitive than the non-wavelength opponent neurons. This is the result of some wavelength distributions favouring excitation instead of inhibition. Both excitation and inhibition would be features of a neural substrate during the formation of a second pigment. Overall, the advantage gained from increased sensitivity with wavelength opponency would open up opportunities for future exploitation by mutations and even further improvement.

Invertebrates

Color vision requires a number of

opsin Animal opsins are G-protein-coupled receptors and a group of proteins made light-sensitive via a chromophore, typically retinal. When bound to retinal, opsins become Retinylidene proteins, but are usually still called opsins regardless. Most ...

molecules with different absorbance peaks, and at least three opsins were present in the ancestor of arthropods;

chelicerates The subphylum Chelicerata (from New Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks, and mite ...

and pancrustaceans today possess color vision.

Vertebrates

Researchers studying the

genes responsible for color-vision pigments have long known that four

opsins exist in birds, reptiles and

teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tele ...

fish. This indicates that the common ancestor of amphibians and amniotes (≈350 million years ago) had tetrachromatic vision — the ability to see four dimensions of color.

Mammals

Today, most mammals possess dichromatic vision, corresponding to protanopia red–green color blindness. They can thus see violet, blue, green and yellow light, but cannot see ultraviolet, and deep red light. This was probably a feature of the first mammalian ancestors, which were likely small, nocturnal, and burrowing. At the time of the

Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...

million years ago, the burrowing ability probably helped mammals survive extinction. Mammalian species of the time had already started to differentiate, but were still generally small, comparable in size to

shrew Shrews (family Soricidae) are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to differ ...

s; this small size would have helped them to find shelter in protected environments.

Monotremes and marsupials

It is postulated that some early monotremes,

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

s, and placentals were semiaquatic or burrowing, as there are multiple mammalian lineages with such habits today. Any burrowing or semiaquatic mammal would have had additional protection from Cretaceous–Paleogene boundary environmental stresses. However, many such species evidently possessed poor color vision in comparison with non-mammalian vertebrate species of the time, including reptiles, birds, and amphibians.

Primates

Since the beginning of the Paleogene Period, surviving mammals enlarged, moving away by

adaptive radiation In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic int ...

from a burrowing existence and into the open, although most species kept their relatively poor color vision. Exceptions occur for some marsupials (which possibly kept their original color vision) and some primates—including humans. Primates, as an order of mammals, began to emerge around the beginning of the Paleogene Period. Primates have re-developed

trichromatic Trichromacy or trichromatism is the possessing of three independent channels for conveying color information, derived from the three different types of cone cells in the eye. Organisms with trichromacy are called trichromats. The normal expl ...

color vision since that time, by the mechanism of gene duplication, being under unusually high

evolutionary pressure Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection. It is a quantitative description of the amount of ...

to develop color vision better than the mammalian standard. Ability to perceive red and orange hues allows tree-dwelling primates to discern them from green. This is particularly important for primates in the detection of red and orange fruit, as well as nutrient-rich new foliage, in which the red and orange carotenoids have not yet been masked by chlorophyll. Another theory is that detecting skin

flushing Flushing may refer to: Places * Flushing, Cornwall, a village in the United Kingdom * Flushing, Queens, New York City ** Flushing Bay, a bay off the north shore of Queens ** Flushing Chinatown (法拉盛華埠), a community in Queens ** Flushin ...

and thereby mood may have influenced the development of primate trichromate vision. The color red also has other effects on primate and human behavior, as discussed in the

color psychology Color psychology is the study of hues as a determinant of human behavior. Color influences perceptions that are not obvious, such as the taste of food. Colors have qualities that can cause certain emotions in people. How color influences individ ...

article.Diana Widermann, Robert A. Barton, and Russel A. Hill. Evolutionary perspectives on sport and competition. In Today, among simians, the

catarrhine The parvorder Catarrhini , catarrhine monkeys, Old World anthropoids, or Old World monkeys, consisting of the Cercopithecoidea and apes (Hominoidea). In 1812, Geoffroy grouped those two groups together and established the name Catarrhini, "Old ...

s (

Old World monkey Old World monkey is the common English name for a family of primates known taxonomically as the Cercopithecidae (). Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons ...

s and

ape Apes (collectively Hominoidea ) are a clade of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and as well as Europe in prehistory), which together with its sister g ...

s, including

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...

s) are routinely trichromatic—meaning that both males and females possess three opsins, sensitive to short-wave, medium-wave, and long-wave light—while, conversely, only a small fraction of

platyrrhine New World monkeys are the five families of primates that are found in the tropical regions of Mexico, Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Ceboidea ...

primates (

New World monkey New World monkeys are the five families of primates that are found in the tropical regions of Mexico, Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Ceboidea ...

s) are trichromats.Surridge, A. K., and D. Osorio. 2003. Evolution and selection of trichromatic vision in primates. Trends in Ecol. and Evol. 18: 198-205.

References

* {{vision in animals Color vision

Colour vision Color vision, a feature of visual perception, is an ability to perceive differences between light composed of different wavelengths (i.e., different spectral power distributions) independently of light intensity. Color perception is a part of ...