[extropy-chat] Color vision (was: evolution again)

Acy James Stapp astapp at fizzfactorgames.com
Tue Nov 30 17:33:57 UTC 2004


Amara Graps wrote:
>> Now, what if humans preferentially chose partners
>> with larger penises?  This would explain why humans
>> have larger penises than chimps, would it not?
> 
> size, but what about COLOR ?
> 
> Here is proof that the Vervet monkey is _not_ color-blind
> (*)  http://www.amara.com/notcolorblindmonkey_med.jpg

Old world monkeys and apes have trichromatic vision like humans. New
world monkeys have a variety of color visions; some are trichromatic
(howler monkey); some nocturnal species are monochromatic, and most
interesting are the polymorphic species where color vision is
sex-linked: males have BG, BY, or BR vision while females can be BG,
BY, BR, BGY, BYR, or BGR.     

Up to half of human females are tetrachromatic to some extent. This
involves having two versions of the red or green photopigments on
different chromosomes. In a particular cell the gene has a 50% chance
of being expressed from either chromosome, and if they are different
the woman will be tetrachromatic. Try counting the color bands in a
rainbow; seven is the traditional number for trichromats and some women
percieve up to ten!  In fact, it seems to me that by having different
red and green pigments some women could be pentachromatic. The extra
colors would likely be a yellow of som etype.        

There is some research that indicates that all humans are
tetrachromatic to UV in the retina but that ultraviolet light is
blocked by the lens. Humans can sense polarization, but only across
the entire field; google "Haidinger's Brush".

Most vertebrates have four classes of cones; some more, some less. The
mesozoic mammals that we evolved from had two, as they were nocturnal
and color vision was not that important. We've reevolved trichromatic
vision since then. Many birds are pentachromatic, but the mantis shrimp
is the color vision champion. It has eight color pigments and color
filters in the receptors to further increase the gamut. They also sense
polarization of light much more efficiently than humans.
additional polarization and 



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