This paper examines the evolutionary development of color vision across vertebrate species, tracing its origins from primitive light-sensitive cells to the sophisticated trichromatic systems found in humans and Old World primates. The paper explores the molecular basis of color detection, the role of opsins and cone cells, and the divergence between dichromatic and trichromatic vision. It surveys competing theories about why trichromacy evolved — including fruit detection, leaf selection, and reading social cues — and discusses trade-offs such as the decline in olfactory sensitivity. Drawing on studies of primates, birds, and other vertebrates, the paper argues that color vision is a latent genetic trait shaped by ecological niche rather than a uniform evolutionary progression.
Color vision is one of the most striking and somewhat mysterious developments in the evolutionary history of vertebrates. While most of us take it for granted and probably view it as a rather straightforward developmental step in evolution, it is anything but a linear, step-by-step progression. The development of the eye itself does appear to have been a basic progressive evolutionary advance, probably starting out as a light-sensitive pigment spot on smaller organisms and then proceeding to become differentiated into more light-sensitive cells, which gradually coated the inside of a slowly forming eyeball to finally become what we now know as the retina. The early retina was probably at first sensitive only to movement and changes in light intensity, but eventually the ability to see color was acquired (Seashore 35). The retina-eye configuration is generally a standard evolutionary development in all vertebrates and many non-vertebrate species as well (see Figure 1).
However, at this point the story of color vision development becomes as varied as the rainbow itself. Color vision is not something that evolved homogenously across all species phyla over time. Instead, at first glance it almost seems a random development, appearing in some species while bypassing others. Some species' ancestors possessed one type of color vision while their descendants seem to possess a completely different type, or lost color vision altogether. Divergences and parallel developments appear to be the norm in the evolution of color vision. There are many theories and changing views on this development, from hardcore Darwinists citing ecosystem survival strategies to Creationists who hold the eye up as a product only possible through intelligent design.
It is helpful to review the eye and color vision in their current state of development in vertebrates, humans among them. Straight-line evolution would seem to suppose that all vertebrates, being higher on the evolutionary scale, would have developed a somewhat identical color vision strategy. This is not the case. Instead there is a wide variety of perceptual thresholds in vertebrates across phyla, from seeing only in black and white to distinguishing even more colors at higher and lower wavelengths in non-human species. As Matthen observes: "Considered across biological taxa in all of its occurrences, colour is a heterogeneous collection of perceptual concepts generated from wavelength-sensitive data for a variety of specialized purposes by cognitive systems with different neurocomputational structures and evolutionary histories" (186).
According to Matthen, color vision development is a "disunity" (186) rather than a unified field of development that progresses evenly in all life forms. He elaborates:
"There is neither a single phenomenology of colour vision nor a set of shared concepts that defines colour wherever it may occur. There is a commonality in the informational material from which colour concepts are constructed; this is inherited from the opsins that constitute the basis for any colour-vision system. Consequently, there is a functional commonality in the mechanisms that are needed to gather this information, but, as the Disunity of Colour Thesis stated at the start of Chapter 6 implies, no one mind-independent property that all colour perceivers track or detect, no one ecological problem they all try to solve." (Matthen 186)
In trying to discover the evolutionary necessity of color vision, researchers have always had to generalize about the survival benefits of that perception.
At present, humans, other apes, and Old World monkeys have trichromatic vision. This means that we have eyes containing three color receptors sensitive to blue, green, and yellow-red light. These receptors allow us to distinguish approximately 2.3 million colors. Most other mammals on the planet have receptors for only blue and green and can subsequently distinguish far fewer colors (Kleiner 12). "New World primates' vision changed, too, but not to full trichromacy. In most of these animals, some of the females discern reds and yellows from greens, but males don't" (Travis 236).
Each light-sensitive cell of the human eye responds to a specific wavelength of visible light. Interestingly, the same chemical component is used in the detection of each particular color: a molecule called 11-cis-retinal is the single chemical component that absorbs light in any receptor cell. It is the larger protein molecule to which this component is attached that determines the specific wavelength of light it absorbs (Color Vision 427).
The human retina contains two classes of light-sensing cells: "rods" (which perceive shades of grey and are most useful in twilight and low light) and three kinds of "cones," each sensitive to a particular wavelength. Interpreted by the brain, these three wavelengths become the three primary colors of vision: red, blue, and green. When the information received by the cone cells is combined, the world is revealed in all the subtlety and splendor of its full color spectrum (Savage 47). Furthermore, we perceive only a very narrow band of the electromagnetic spectrum, in the small range of 400 to 700 nanometers.
Initially it was thought that vertebrates see color by the brain comparing the strength of the signals from each of the receptor cells, thereby separating the color wavelengths. (Interestingly, this theory does not explain the perception of colors such as gold, silver, and brown.) The more recent opponent-process (O-P) theory states that we perceive colors in opposing pairs such as blue and yellow, and red and green. In O-P theory, too much blue light is thought to reduce one's awareness of yellow, and too much green reduces the awareness of red, and vice versa. Studies are leaning toward a combination of theories, speculating that the brain further processes these signals in terms of opposing pairs (Color Vision 57; Chatterjee & Callaway 668).
Vertebrates began to appear between 530 and 510 million years ago during what is called the Cambrian Explosion, a period during which the fossil record shows a rapid outcropping of differentiated species development. "The first tetrapod (an animal that has four limbs, along with hips and shoulders and fingers and toes) crawled out of the Earth's oceans some time between 375 and 350 million years ago" (Seashore 427). Species at this stage could see light as black and white, or within a yellow-blue range and all the varieties that range produced. Some vertebrates could also perceive ultraviolet light and had an orange-red cone receptor as well, but these subsequently vanished around 200 million years ago. As the ages passed and dinosaurs ruled the earth, most vertebrates possessed limited color vision, having only blue cones, yellow cones, and black-and-white rods: "Back in the late Cretaceous, early placental mammals saw the world in limited colors, much like humans with red-green color blindness do" (Moffat 613).
Then, about 40 million years ago, a divergence in the way the retina and color vision were forming had developed. This was shortly after mammals and then primates had appeared in the evolutionary scheme of things. Two specific branches of color vision development took place: dichromatic (two-color) and trichromatic (three-color) vision.
When it comes to their color vision, people fall between birds and most mammals. As Travis notes: "People generally have three opsins [retinal pigment proteins], which are sensitive to blue, green, and red. In fact, most of the primates that evolved in Africa and Asia, including the great apes and chimpanzees, are fully trichromatic. In contrast, most New World primates, such as the tamarins and marmosets of South America, are dichromatic, having just blue-sensitive and green-sensitive opsins" (235).
Although these two branches of primate vertebrate development occurred concurrently, the difference in color vision has largely persisted to the present. Researchers have noticed a notable trade-off associated with the human achievement of trichromatic vision: our sense of smell is certainly much less acute than that of other species that are dichromatic or monochromatic (perceiving only black and white). Approximately sixty percent of the mammalian olfactory receptor genes in humans are dormant.
In other simians and Old World monkeys, only about thirty percent are dormant. However, in mice and dogs, which lack trichromatic vision, only around twenty percent of their olfactory genes are non-functional. This gives them an eighty percent functional olfactory system compared to less than half that in humans (Kleiner 12). Furthermore, it is clear that most ground-living mammals are colorblind. "These facts support the evidence from other sources which shows that vision is of secondary importance in the life activities of all the mammals except the tree-living primates and man, who evolved from arboreal stock" (Guilford 40).
In a recent study, researchers measured the number of non-functional olfactory receptor genes in 18 species of ape and monkey and in people. Primates with trichromatic vision all had a significantly worse sense of smell than monkeys without it. The finding that helped clinch the case was the New World howler monkey: it is the only New World monkey with full trichromatic vision, and the researchers found that it also has the worst sense of smell among New World monkeys, with about 31 percent of its olfactory receptor genes being non-functional (Kleiner 12).
There is another interesting evolutionary difference between humans and our avian cohabitants. Even though birds are also trichromates, they do not use the same protein for detecting the color red. The primate version of this opsin apparently arose spontaneously in Old World primates from a mutation of the green opsin gene on the X chromosome some 30 to 40 million years ago (Travis 235). Researchers have also concluded that the "evolutionary ancestor common to both had four distinct opsins. Early mammals then lost two of them, probably with little ill effect because these creatures were nocturnal and had a limited need to discern colors" (Travis 235).
This is one of the most remarkable aspects of trichromatism: the few types of animal species that possess it are also widely separated phylogenetically. Among mammal phyla, only some primates have trichromatic vision. The wide phylogenetic separation of differing color perception abilities suggests that color vision is a latent trait in almost all evolutionary groups — a genetic trait that can emerge when conditions call for it. However, if one examines dichromatic species as opposed to trichromatic species, there is no direct line of descent linking the two to a common ancestor with color vision. It would appear that color vision arose independently in these two different phyla, rather than having a linear origin in an earlier common ancestor (Matthen 177). This certainly poses difficulties for strictly linear models of Darwinian evolution.
Recent studies may, however, contradict the separate development theory. Scientists have isolated the gene that controls the formation of the eye in flies and have successfully switched on this master gene to grow "extra" eyes on a fly's body. This suggests an intriguing interconnection for the original development of the eye and perhaps even color vision: "Although the human eye and the fly eye are vastly different, the similarities between the gene for a fly eye and that of a mammalian eye lead to a theory of a primordial eye that may have evolved only once and taken on different designs to accommodate the needs of the organism" (Silverston 14).
While trichromatism is one of the most important distinctions of human vision, there is another equally significant characteristic: humans experience highly predictable contrast and fatigue effects (Gordon 79). As Gordon describes: "If a red square is placed on a grey ground and fixated for a few moments, one comes to see a greenish tinge surrounding the red. An intense green light induces a reddish after-image; blue light induces yellow, and vice versa (note that red and green and blue and yellow are complementary hues in that they mix to form neutral greys). Anyone can experience these effects by simply staring at a coloured light (not the sun) for a few moments and then looking at a white surface" (79–80).
"Competing theories: fruit, leaves, and social signaling"
"Trichromacy advantage tested in tamarin experiments"
While the retina had evolved from a mere light-sensitive lump of protoplasm to a more sophisticated organ with photoreceptors and the ability to discern motion, color vision has developed disproportionately and with wide variation across all species. If color vision is a latent genetic possibility inherent across all species phyla, then why do not all species possess it?
You’re 68% through this paper. Sign up to read the remaining 2 sections.
Sign Up Now — Instant Access Already a member? Log inAlways verify citation format against your institution’s current style guide requirements.