Some Women Really Do See the World Differently...

Last fall, the Pittsburgh Post-Gazette ran a story on tetrachromats, people who can see four distinct ranges of color (instead of the three with which most of us live.) At this point, it is believed that only women have the potential for super color vision.

Each of the three standard color-detecting cones in the retina -- blue, green and red -- can pick up about 100 different gradations of color. But the brain can combine those variations exponentially, so that the average person can distinguish about one million different hues.

A true tetrachromat has another type of cone in between the red and green -- somewhere in the orange range -- and its 100 shades theoretically would allow her to see 100 million different colors. But because most people's eyes aren't capable of seeing the world the way a true four-color viewer perceives it, there's little way of knowing how many advantages that might give to the tetrachromats.

Scientists estimate that 2 percent to 3 percent of the world's women may have the kind of fourth cone that lies smack between the standard red and green cones, which could give them a colossal range. This means there could be 99 million women in the world with true four-color vision.

Why only women? The genes for the pigments in green and red cones lie on the X chromosome, and only women have two X chromosomes, creating the opportunity for one type of red cone to be activated on one X chromosome and the other type of red cone on the other one. (In a few cases, women may have two distinct green cones on either X chromosome.)

However, it's unlikely that all of the women with four types of color cones will have the potential for superior color vision. This is because for many women, their two red cones will be so close to each other in the wavelengths they detect that they won't see things much differently than a typical three-color person does.

But before they pat themselves on the back for their superior evolution, says the newspaper, it's important to note that humans are just getting back to where birds, amphibians, and reptiles have been for eons.

Even so, it's fascinating to think how many women artists might be tetrachromats.