Color Range Perception, Evolution of the Eye:

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Color Range Perception, Evolution of the Eye:

Jul 21 2011 10:15:55 am EST

Topics: Evolution, Morphology, Science,

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From the entire range of the electromagnetic spectrum, most life that can perceive light evolved to perceive a narrow band—the visible light spectrum (400 nm-700 nm). This range of perception is based on hundreds of millions of years of adaptation.

An interesting phenomenon of the visible spectrum is that it penetrates water by about 6 orders of magnitude better than adjacent frequencies. In other words, the visible spectrum penetrates water much better than other frequencies. This phenomena is demonstrated in the graph below (Fernald, 1997).

Early aquatic life adapted to perceive these frequencies. Interestingly, as life evolved on land, where a broader range of frequencies is visible, the eye remained sensitive to this narrow range. Whether the mechanism for detecting a broader range of frequencies is too complex, or there is no distinct evolutionary advantage, life remains sensitive to this narrow range.

Within this range, organisms perceive light in different ways, based largely on evolutionary pressures. A simple organism, such as the planarian, may only be able to detect the presence of light, whereas more complex organisms utilize rod and cone cells to distinguish shades and gradients.

According to Jay Neitz, a professor of ophthalmology and a color vision researcher at the University of Washington in Seattle, each of the three standard cone cells in the retina, blue, green, and red, can perceive 100 gradients of color. While an organism possessing only one type of cell would be able to see only 100 colors, an organism possessing two types would see 10,000 colors, and an organism possessing all three types would see a million colors.

The seal is an example of a monochromat—it possesses only one type of cone cell, and thus, can only perceive one spectral color. The owl monkey is another monochromat. Most mammals are believed to be dichromats, possessing two different types of cone cells, and capable of detecting two spectral colors. In combination, a dichromat would be able to detect 10,000 colors.

Humans and closely related primates posses trichromacy—possessing three different type of cone cells. It is believed that trichromacy may provide an evolutionary advantage for detecting the ripeness of fruits and leaves.

Certain animals and insects posses the ability to detect ultraviolet light. They may be trichromats, favoring an ultraviolet cone cell over, say, a red cone cell. Others may be tetrachromats, possessing all the cone cells of human vision, in addition to ultraviolet. Pollinating insects such as bees posses the ability to detect ultraviolet light. Flowers often display nectar guides visible only in ultraviolet light, giving a UV detecting pollinator a distinct advantage.

The mantis shrimp has perhaps the most impressive eyes of the animal kingdom. They posses the ability to detect ultraviolet radiation, as well as infra-red and polarized light. There are many potential reasons for their impressive sight, including the ability to recognize different coral, prey, predators, and even to detect phases of the moon for mating. Their superior vision also plays a role in communication, as some species use fluorescent patterns on their bodies to communicate.

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