Our color vision is based on three types of receptors (cones) which are sensitive to three distinct locations on the spectrum: 420–440 nm, 534–555 nm, and 564–580 nm. We label them "red", "green", and "blue", but these names are arbitrary. However, their locations on the spectrum may not be arbitrary.

I notice that they correspond to the colors of the three most important things in our natural habitat: sky (the above), vegetation (the below), and blood (the sign of potential food or alarm, depending upon whether you are the hunter or the prey).

Am I on to something here, or am I just dreaming in technicolor?

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    $\begingroup$ It is proposed by various groups that color vision developed due to its evolutionary benefits in enhancing the recognition of (ripe) fruits. I think it's all highly speculative but I can dig up some articles if needed. The evolutionary benefits of recognizing sky seems remote, especially for terrestrials. Recognizing the color of blood makes no sense as prey is most often not yet bleeding and wounds are recognized through pain. Rather, the 3 cone types and with color opponency enable the visual system to see many colors in the visible spectrum, that reportedly help to recognize fruit. $\endgroup$
    – AliceD
    Dec 3 '14 at 1:24
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    $\begingroup$ Fruit! I hadn't thought of that. I guess that does make a lot more sense than sky. Thanks, Chris. $\endgroup$
    – SlowMagic
    Dec 3 '14 at 1:29
  • $\begingroup$ And most mammals don't have the receptors to see blue light. But flowering plants are relatively recent, do non-flowering plants make colored fruits? $\endgroup$
    – user137
    Dec 3 '14 at 15:06
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    $\begingroup$ Also, I think dogs and some other predator animals lack red cone cells in their eye due to never having the pressure to need to easily detect berries (often red). [Citation needed] I have never heard anything about needing to see blood as a sign of alarm/food. Emphasising what @ChrisStronks said, if an animal is bleeding so heavily that it can be seen at distance, odds are as a predator that your job is done. As for tracking/alarm, smell would and does serve much better for animals +doesn't require staring at the ground as much. $\endgroup$
    – James
    Dec 4 '14 at 1:22

Short answer
Color vision is not based on a calibration to the sky, vegetation and blood. The current leading theory of the development of trichromatic vision in humans is based on the foraging of fruit in our primate ancestors.

The places of red, green and blue wavelengths in the spectrum are physically defined and, therefore, not arbitrary; see this question on Biology SE.

Before continuing, it is good to mention that trichromacy (the presence of red, green and blue cones in the retina) is typical for primates. For example, dichromacy (<500 and >500 nm cones) is the most common configuration in mammals. The split in red and green photopigment in primates developed relatively late in evolution (30-40 mln years ago), inferring trichromacy in primates from a dichromatic ancestor. Note that many avian and aquatic species may be tetrachromats or up (4 or more photopigments) (Nathans et al. 1999), with the mantis shrimp featuring no less than 10(!) different photopigments (Cronin & Marshall, 1989).

It is believed that the red-green-blue system in primates has evolved due to its benefits for identifying fruit on a background of foliage, and to assess the ripeness of fruits. The food of monkeys typically consists of fruit, and young leaves. Young leaves are light-green, while ripe fruits are often yellow (e.g., bananas) and orange (e.g. oranges, mangos) (Osorio & Vorobyev, 1996). Unripe fruits typically contain chlorophyll and resemble the color of foliage (green). Hence, to discern ripe, nutritious fruits (yellow-orange or 570-620 nm) from foliage (green or 495-570 nm - frequencies mentioned were copied from wikipedia), it makes sense to have good resolution in the red-green area. The red opsin has its maximum at 530, and the green at 560 nm. The blue has its peak a lot lower at 425 nm (Nathans et al. 1999). Hence, the red and green opsins, which evolved late in evolution, are both right in the "ripe fruit area" and have absorption spectra very close together. Hence, there is a lot of color sensitivity (high color resolution) in the red-green area, which covers reds, oranges, yellows and greenish colors. This gives primates a very high sensitivity to recognize fruits, and especially ripe fruits in a green background. The resolution in the green-blue range is smaller (blues, purples).

As a background: color vision in trichromats works by color opponency, and specifically a yellow-blue and red-green color opponency. This means there exists no yellowish blue hue, or a reddish green (De Valois & De Valois, 1993). The red-green opponency means that we have exquisite sensitivity in the red-green pathway, as red cones suppress green cone output and vice versa. In other words, there is a high color acuity in the red-green area that helps to recognize fruits.

As a side note: The trichromat color vision scenario in primates supports the notion that cats (for example), being predators with dichromatic vision, do not benefit from being able to identify ripe and unripe fruits, as mentioned by @GoodGravy. In contrast, cats need excellent night vision and motion sensitivity, being nocturnal hunters. Indeed, color vision versus night vision, and color vision versus high motion sensitivity are both trade-offs that do not go hand in hand (Kelber et al, 2002).

- Cronin & Marshall, Nature (1989); 137-40
- De Valois & De Valois, Vis Res (1993); 33(8): 1053-65
- Kelber et al., Biol Rev (2003); 78: 81–118
- Nathans et al., Neuron (1999); 24(2): 299–312

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    $\begingroup$ Thank you, @ChrisStronks. This is a wonderful answer. I have heard about the mantis shrimp and its numerous color receptors. Amazing! It makes you wonder what their experience of the world is like. I've seen multispectral and hyperspectral imagery. It's an overwhelming amount of information. Anyway, thanks again. I'm now in the mood for some fruit... $\endgroup$
    – SlowMagic
    Dec 6 '14 at 13:49

Is our color vision calibrated to sky, vegetation, and blood? TL;DR; No

Normal person has 3 types of detectors in his eyes called cones that are responsible for color vision. Cones can be: red (only name), green, or blue. They do not respond to single color but rather to range of frequencies. Under few layers of specific cells they connect to optic nerve and nerve transmits signals to the brain. (This is simplified version as same nerves are responsible also for intensity) Based on intensity (how much nerve fires) of signals from different color nerves brain is capable of figuring out what color it really is. Every type of cone has it's responsive frequency range. enter image description here

If you would look at the samples below of peak ranges, it makes it pretty visible that Red cones peak at what normal person perceives as yellow (it could be 👽 blood though :) ) and not red, while blue cones peak at very intense blue-violet that sky isn't, green is on the right track though.

So I must regretfully say that a very 'romantic' theory on vision calibrated to sky, vegetation, and blood cannot be right since 'red' cones in fact respond to yellow light.

Blue cones peaks

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Green cones peaks

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Red cones peaks

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Here, you can find the tool that I have used to get RGB/Hex values from wavelengths.

  • $\begingroup$ Would downvoter care to elaborate where did I go amiss? $\endgroup$ Sep 14 '16 at 12:24

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