Re: Why are blue cones rare in humans?


"pete" <vincent@xxxxxxxxxxxxxxx> wrote in message
news:ep3rb6$9ek$2@xxxxxxxxxxxxxxxxxxxxxxxxx
on 20 Jan 2007 08:29:53 -0800, John Roth <JohnRoth1@xxxxxxxxxxxx> sez:

Marc Verhaegen wrote:
http://www.newscientist.com/article.ns?id=dn664

Uh, Marc - blue cones aren't rare in humans. The most
prevalant form of color blindness is due to a loss of one
of the red cones, and that's because the gene is on the
X chromosome.

http://en.wikipedia.org/wiki/Color_vision

Color vision is interesting. It turns out that mammals
in general only have two types of cone while reptiles,
insects and birds have four. Somehow, early mammals
lost two of them. Why? No idea.

Old world monkeys picked up a third type, while new
world monkeys didn't.

Lots of animals have cones that are sensitive to different
parts of the spectrum. Pictures of how the world actually
looks to various species of bird can be fascinating: there's
a fairly famous picture of a black-eyed Susan (a kind of flower)
that shows a band around the outside that's only visible in
the ultra-violet. Trying to figure out what various birds and
other animals actually see is a current (if somewhat minor)
research topic.

There are a few people with four varieties of cone. What
I find amazing is that their brains get properly wired to handle
four color vision.

Do you have a reference for that? I confess I find it rather
hard to believe - it suggests there are people around who
see colours the rest of us don't get to experience. They'd
get to invent their own names for them...

Some people also have an extra gene for the color green and yes people seem
to be rather more variable in color vision than might be expected. Why don't
you just google it?





--
==========================================================================
vincent@triumf[munge].ca Pete Vincent
Disclaimer: all I know I learned from reading Usenet.


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