Scott Seidman wrote:
rw wrote in news:44c55670$0$24181
:


Primates (including humans) apparently re-evolved a third type of cone
(toward the blue end of the spectrum), probably because they had to
distinguish between different types of ripe fruit.




Some primates have interesting dimorphisms. In the squirrel monkey, for
example, all of one sex are trichromats, and something like 70% of the
other sex are bichromats.

Interesting.

Red-green color blindness is far more common in men than in women.
That's because the genes for the red and green cones are located on the
X chromosome, of which women have two and men have one. A woman can have
one defective X chromosome and still have normal color vision, because
the other chromosome will make up for it.

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