The world may appear a more colorful place to women, according to a new study that finds many women perceive a greater range of colors — particularly shades of red — than men are able to see.
How men and women see the world appears to relate back to evolution and our early ancestors. While men likely were scoping out the landscape for prey to hunt, the researchers theorize that women were gathering fruits, vegetables, insects and other edibles often identified and rated by color.
For the study, which will be published in September in The American Journal of Human Genetics, researchers analyzed the DNA of 236 men from a number of populations from Africa, Asia and Europe.
The scientists focused on a particular gene, OPN1LW, which codes for a protein, called an opsin protein, involved in the detection of the red light spectrum. This gene also exchanges amino acids — the building blocks of protein — with a nearby gene involved in detecting the green spectrum of light.
Within the test group, the researchers found 85 variations of the OPN1LW gene, three times more genetic variation than for any other human gene.
Study authors Brian Verrelli, a postdoctoral fellow at the University of Maryland and an assistant professor at Arizona State University, and Sarah Tishkoff, an assistant professor of biology at the University of Maryland, told Discovery News that the high rate of variation was maintained by natural selection.
"Natural selection could have maintained these genetic differences at the red opsin gene thousands of years ago, and this is why we still see them in a large proportion of people today," Tishkoff and Verrelli told Discovery News. "It is estimated that a number of people today — we estimate about 40 percent of women — have (an) added color perception ability; however, it is unclear whether natural selection still operates today to maintain it."
They explained that X chromosomes could have two types of opsin — perceiving either shades of true red, or shades within the red-orange range. Men have one X chromosome and one Y chromosome, so they only have one of the two types of red-detecting opsin.
The limit, and possible problems with amino acid exchanges, sometimes result in color blindness, which now affects eight percent of all men.
Women can possess both opsin pigments because they have two X chromosomes. According to Tishkoff and Verrelli, the 40 percent of women who do possess both have superior color perception for reds, and possibly other colors. That is because contrast enables humans to distinguish between various colors.
Visual skills among the sexes could balance out, however, because the same genes that affect color recognition might also influence depth perception and visual acuity, which some men could excel at over women.
In prehistoric times, color perception could have meant the difference between nourishing foods or deadly morsels.
"The added color perception would be a benefit to (women) and their offspring if it helps with possibly distinguishing edible berries and fruits from green background foliage, to distinguish ripe fruits from unripe ones, or even to distinguish nonpoisonous plants from poisonous berries," said Tishkoff and Verrelli. "This added color perception may explain how hunter-gatherer techniques became so common in humans."
Since the genetic component of vision does not take into account how our brains process colors, it is possible that every person literally sees the world in a somewhat different way.
Animals, fish, birds and insects may see things even more differently. Tishkoff and Verrelli said that organisms living in the deep ocean, for example, have several types of blue opsins that enable them to see innumerable shades of blue.
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