Seeing Red: Genetics and Color Vision
Seeing Red: Genetics and Color Vision

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Few phenomena are more remarkable or complex than the sensation of color. It pervades every moment of our lives, from the red-orange of sunrise to the depths of our dreams. Even our emotions reflect the sensation of color. We "feel blue," grow "green with envy" and "red with anger." A recent discovery sheds important light on one aspect of human color vision – that of seeing red.
     It has long been known that men suffer color blindness at greater rates than women. While some eight percent of men are afflicted by this malady, color blindness occurs in but 0.5% of women. Despite these numbers, we always took solace in the fact that, among color normal individuals, there were apparently no important differences between the abilities of men and women.
     Not so fast, says Brian Verrelli of Arizona State University and Sarah Tishkoff of the University of Maryland. According to their recent study, even men who aren't color blind may see the world differently than women. And guess who picked the short straw? That's right, guys, it's us. Seems those old stereotypes about women having a superior sense of color may be true after all.

Red fruit

Figure 1. Does the often-superior red sensitivity of women's color vision result from a need to distinguish edible from poisonous fruit? And should wholesale ruby dealers now be considering hiring more women? Photo: R.W. Hughes; fruit by Joan Allen

     The scientists focused on a gene that allows humans to see red, a gene found only on the X chromosome. Variations in this gene can allow expanded color vision. Since men have only one X chromosome compared to the two women possess, they get one less crack at this expanded vision.
     According to a recent article:

Brian Verrelli of Arizona State University and Sarah Tishkoff of the University of Maryland analyzed genetic data from 236 people from around the world. Specifically, they studied a gene on the X chromosome known as OPN1LW, which codes for a protein that detects visible light in the red spectrum. Exchange of material between this gene and a neighboring gene associated with green light leads to a high amount of genetic variation but can result in color blindness if the process goes awry. Among the study participants the researchers found 85 variants of the gene. "That's approximately three times higher than what you see at any other random gene in the human genome," Tishkoff says. "Usually it's a bad thing to have too much change in a gene, and natural selection gets rid of it. But in this case we're seeing the reverse."

     Such variations have been preserved throughout evolution and are thought to be beneficial. The two scientists speculate that it might have begun in the prehistoric era, where acute color vision was of use in separating poisonous crimson berries from their edible burgundy cousins. Since women did much of the gathering (while men did the hunting), women developed better red sensitivity.

 

About the authors

 

Richard Hughes in Tibet
Richard Hughes
(left) is the author of the classic Ruby & Sapphire and over 100 articles on various aspects of gemology. Many of his writings can be found at www.ruby-sapphire.com.

 

John Koivula

John I. Koivula is one of the world's most famous gemologists and photomicrographers. Author of several books and more than a thousand articles, he was also the scientific advisor to the famous MacGyver television series.

Notes

First published in May 2005, while John and I were at the AGTA GTC. Working with John was one of the greatest pleasures of my life, sadly far too brief. Looking back, I can only wonder what might have been… Thanks to Donald Allen for suggesting the above article.

 

 

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Posted 14 October, 2011; last updated 7 March, 2013