The Secret Past of Color Vision
Look around you. Everything we see contains thousands, if not millions of hues. However, the way in which color vision came about remains a mystery. While various theories have arisen, the answer to why we see the world as we do remains unknown. Various arguments, including that of Mark Changizi and Aline Bombas, attempt to explain this phenomenon. Despite there still being no concrete answer, Bombas’ theory as to why humans developed color vision is more feasible than Changizi’s because it takes a “bigger picture” approach, one that coincides with the theory of natural selection.
Changizi argues that our vision evolved to view changes in other’s facial hues from their “baseline” color. Observations of changes in facial color provide useful insight into the physical wellbeing of others. Being able to understand what these deviations meant would be advantageous because we would be able to nourish those who are visibly sick or ailing, thus avoiding the species’ extinction. However, this theory directly opposes the theory of natural selection. The care of others in a polychromatic population would cause the passing down of their traits, leading to a possibly more ailing population that doesn’t necessarily have better color vision. Furthermore, if one was the only trichromatic individual in their population, the others would not be able to recognize this skin color change, and the trichromat could possibly die due to an illness and lack of care, terminating the trait. Changizi supports his argument with quantitative research on the sensitivity of our eyes in relation to the reflection of the skin. He found that cones designed for medium and long wavelengths, the ones that give us color vision, are extremely sensitive to wavelengths that portray the different oxidation and blood levels of the skin, tones that depict different conditions. This suggests that our vision has developed to more accurately read skin tones; however, one must consider other reasons why our vision is more specialized in this range.
On the contrary, Bombas focuses on various types of dichromatic and trichromatic primates, (including humans), many of which reside in the tropical rainforest. Her team’s research focuses on the use of color vision to distinguish fruit from surrounding foliage. According to their research, those who can see colored fruit against a monochromatic background, trichromats, have better speed and accuracy during foraging. When researching common fruits found in the rainforest, I found many contained the same, if not similar, coloring of the human skin. These include “avocados, coconuts, figs, oranges, lemons, grapefruit, bananas, guavas, pineapples, mangos, and tomatoes; vegetables including corn, potatoes, rice, winter squash and yams” (rainforestmaker.org). While one may argue that they have never seen skin tone resembling that of a grapefruit, it important to remember that our eyes are most sensitive to wavelengths in baseline-like ranges of the red, blue, green, and yellow spectrum. The color of our skin resembles that of hidden fruits in the tropical rainforest, leading to the possibility that our eyes are extra sensitive in that range of skin tone because of our early need to find hidden skin-colored fruits.
Unlike Changizi, Bombas’ research complements the theory of natural selection. He states that “…trichromats accepted (i.e. ate) more of the fruit they picked, sniffed fruit less, and had shorter foraging sequences than dichromates did. However, this apparent advantage for picking fruit does not appear to translate into consuming more food overall in trichromatic Capuchins or spider monkeys” (Bombas, Kendall, Sumner, 2013). Although the trichromatic monkeys did not consume more food than their dichromatic counterparts, they were able to finish their foraging sequences faster, allowing for more time to care for their children or socialize with their pack. Foraging can also put animals in vulnerable positions, so by foraging faster, trichromats were less susceptible to predation. In this way, color vision correlates with safety from predators and increased care for youth, making it a favorable trait to be passed down to the next generation.
While no one can definitively say why we developed the color vision we have today, the theories that have arisen are intriguing. Ultimately, self- sustainability is what drives the process of evolution, and if color vision aids this process, it will be passed down to future generations.
Bompas, Aline, et al. “Spotting Fruit versus Picking Fruit as the Selective Advantage of Human Colour Vision.” i-Perception, vol. 4, no. 2, 2013, pp. 84–94., doi:10.1068/i0564.
Changizi, Mark A. The Vision Revolution: How the Latest Research Overturns Everything We Thought We Knew about Human Vision. Benbella Books, 2010.
“Rain Forest Maker.” RainforestMaker – Grow Back the Earth’s Rainforests, www.rainforestmaker.org/facts.html.