The Super-Seers Who Live Among Us

By Veronique Greenwood | June 18, 2012 11:18 am


The ancestors of modern humans developed color vision 30 million years ago. But it was not until the late 1700s that there are records of anyone seeing colors in an unusual way. English chemist John Dalton, who found that people thought he was joking when he asked whether a geranium flower was blue or pink, wrote a description in 1794 of what he saw for the Manchester Literary and Philosophical Society journal: His world was suffused by shades of blue and yellow, but contained none of the mysterious sensation known as red. “That part of the image which others call red,” he wrote, “appears to me little more than a shade or defect of light.” It was one of the first mentions of colorblindness in human history.

In the centuries since, we have discovered what it is that robs some people of such sensations. Those of us with standard vision, called trichromats, have three kinds of pigments, or cones, in our retinae, each sensitive to a certain range of light and spaced out across the visible spectrum so that they can together convey to the brain everything from red to violet. In the colorblind, a mutated cone is so close to another in sensitivity that parts of the spectrum aren’t covered, or there are only two functioning cones, a condition called dichromacy. A difference of one cone causes a serious change in the number of discernable colors: Dichromats see on the order of 10,000 colors, trichromats on the order of a million. But that isn’t the end of the story. Recently, as genetic analyses and tests of color vision have grown more sophisticated, we are stumbling into one of the most curious discoveries in vision since Dalton’s day. Dichromats have 2 cones, trichromats have 3, tetrachromats have 4, making them theoretically capable of seeing 100 million colors.

A footnote in an obscure vision paper led neuroscientist John Mollon of Cambridge University and his collaborator, Gabriele Jordan of Newcastle University, to ask two decades ago whether such people exist. Two years ago, they found one.

Read the article in Discover’s Invisible Planet issue.

Color image via iStockphoto

  • amphiox

    Note that it is the same gene which causes red-green colour blindness in males (dichromacy) that produces tetrachromacy in females. Perhaps this may explain, to an extent, the persistency of red-green colour blindness – it is actually an advantageous mutation to have in some individuals.

  • ChasCPeterson

    No, tetrachromacy is related to anomalous trichromacy, not to true dichromacy. But it’s true that anomalous trichromacy is the most common form of R-G colorblindness in males.

  • Torbjörn Larsson, OM

    I think this was anticipated when they could get rats to become trichromatic by giving them cones with new pigments. (Grafts or genes, can’t remember.)

    What a hard hit on platonist philosophers with their extranatural/supernatural “qualia”!

    @ amphiox:

    Or RG blindness wasn’t too much of a problem for pre-technology primates, few of which are trichromatic I believe. Say, if trichromatism evolved under the human bottleneck it may not meant too much earlier.

    Today it would be more of a problem I suspect, but there may be sufficient fixes on the way. There is a device for translating colors to sound, developed and used by a RGB blind individual.

  • Andrew

    @ Torbjörn Larsson, OM

    Being that I am not a pre-technology primate, I can’t say this for certain, but as a RG blind male I can say that out in nature I have a much harder time spotting animals and distinguishing between plants than my non-color blind friends. I imagine color blindness was even more of a disadvantage pre-technology.

  • amphiox

    Or RG blindness wasn’t too much of a problem for pre-technology primates, few of which are trichromatic I believe. Say, if trichromatism evolved under the human bottleneck it may not meant too much earlier.

    Trichromatism evolved in old world monkeys and apes (and by a different mechanism in some new world monkeys). As I understand it, it is hypothesized that the ability to see hues of reds became increasingly advantageous for primates whose primary diet is fruit, in order to distinguish things like ripeness.

    The way trichromatism works in some New World Monkeys, where some females are trichromats, while all males are dichromats, however, suggests a possible way in which dichromat males could offset their disadvantage in a social group – namely by watching what the females do, or even stealing from them.

  • Jeff

    An interesting fact missing here is that the “gene” for seeing red entered mammals via a common (today) retrovirus around 30M years ago.

  • jimbo

    I have read some thing on tetrachromats before it has to do with a gene on the X chromosome being different some what. The resulted is some females (having two X chromosomes) may have different genes producing two different cones of near same colors.

  • Thomas Paine

    Radio Lab had a fantastic episode about Colors recently. Highly recommended.


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