Pat and Sean, (01)
Some women actually have four color photoreceptors, instead
of the normal three: (02)
PH> In both these areas, a much richer and more nuanced color
> vocabulary is essential. Maybe this is why women make so many
> color distinctions that are invisible to men (teal, cerise,
> ecru, etc.) (03)
Reptiles and birds generally have four colors, but most mammals
only have two -- probably because they were nocturnal for millions
of years while the dinosaurs were dominant. (04)
Primates have evolved a third color photoreceptor, but human males
who are red-green color blind have reverted to the typical mammalian
two receptors. Marsupials seem to have a third receptor in the
ultraviolet range -- but it's not clear whether they evolved it
or whether they failed to lose it, as the placental mammals did. (05)
However, a tiny percentage of women have four color photoreceptors,
and curiously, mothers of males who have only two are the most likely
to have four. (06)
Following are some web pages on this topic. (07)
John
______________________________________________________________________ (08)
http://www.post-gazette.com/pg/06256/721190-114.stm
Some women may see 100 million colors, thanks to their genes (09)
http://www.rmki.kfki.hu/~lukacs/TETRACH.htm
On tetrachromacy (010)
http://www.cs.utk.edu/~evers/documents/tetraChromat.txt
Looking for Madam Tetrachromat (011)
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