Tetrachromates

While ferreting around on the previous post I found reference to the fact that some women may actually be tetrachromates, seeing four basic colours rather than 3 for normal people or two and a bit like me.

There doesn’t seem to be an awful lot published on the issue, a few papers like this one but not a vast literature from what I can find.

The idea is interesting. There is even the suggestion that it could be expressed in the mothers of colour blind boys, which would have an impact I imagine about whether colourblindness genes were a net negative or positive selection criteria.

For years now, scientists have known that some fraction of women have four different cone photopigments in their retinas. The question still remains, however, whether any of these females have the neural circuitry that enables them to enjoy a different — surely richer — visual experience than the common run of humanity sees. “If we could identify these tetrachromats, it would speak directly to the ability of the brain to organize itself to take advantage of novel stimuli,” says Dr. Neitz. “It would make us a lot more optimistic about doing a gene therapy for color blindness.”

There have been very few attempts to find Madam Tetrachromat. The one that turned up Mrs. M in England, in 1993, was led by Gabriele Jordan, then at Cambridge University and now at the University of Newcastle. She tested the color perception of 14 women who each had at least one son with a specific type of color blindness. She looked at those women because genetics implies that the mothers of color-blind boys may have genetic peculiarities of their own. Among that somewhat peculiar group of women, one could expect to find the odd tetrachromat.

It’s almost as if the supersense these women enjoy comes at the expense of the men in their families. “I’m just sorry I’ve robbed my son of one of his color waves,” Mrs. M says.
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Would there be any practical advantages to tetrachromacy? Dr. Jordan notes that a mother could more easily spot when her children were pale or flushed, and therefore ill. Mrs. M reports that she has always been able to match even subtle colors from memory — buying a bag, for example, to match shoes she hasn’t laid eyes on for months. And computers, color monitors, and the Internet raise a whole raft of possibilities. Just as someone with normal three-color vision surfs rings around a dichromat on the Internet, a tetrachromat, looking at a special computer screen based on four primary colors rather than the standard three, could theoretically dump data into her head faster than the rest of us.