Re: Why are blue cones rare in humans?


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.

John Roth

.

Relevant Pages

  • Re: Why are blue cones rare in humans?
    ... of the red cones, and that's because the gene is on the ... insects and birds have four. ... to be rather more variable in color vision than might be expected. ... "Tetrachromacy has not yet been discovered in any mammals, ...
    (sci.anthropology.paleo)
  • Re: Satellite antenna questions
    ... Use duct tape to cover 2 of your cones, and then find the correct bird with the one you don't cover. ... If your skew and elevation are set properly, and your fence post level says the dish is plumb, then the other birds will be there when you remove the duct tape. ...
    (rec.outdoors.rv-travel)