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Color vision (longish)



On Thu, 20 May 1999, Mickey P. Rowe wrote:

> There seems to be a lot of interest here in color vision (well, at
> least two people are interested in it :-) in dinosaurs and other
> animals.

> Anyhoo, I can't remain completely quiet here in the face of Randy's
> statement:
> 
> > Almost all fish are colorblind,
> 
> That's not likely to be correct.  It's certainly true that most fish
> that humans typically interact with (e.g. around coral reefs, in pet
> stores, on fishing boats) have the capacity for better color vision
> than we do.  The only fish that are likely to be completely colorblind
> are those that live at great depths in the ocean.

Of course, many reef fish (particularly red and orange ones) aren't
normally as colorful as they look under our artificial lights.  Water
absorbs red light strongly, so that what looks like a bright red fish
under artificial illumination may in fact be almost black under normal
lighting conditions.


> > Most livestock are colorblind, I believe that horses are.
> 
> That depends upon how you define "colorblind".  Using the definition
> that we typically use for humans that are "colorblind" it is most
> probably true (not much research has really been done to characterize
> color vision in such animals, but the data that are there suggest that
> horses, cows etc. are like humans with red-green color blindness).

Like me (and a significant proportion of other male humans, including, as
I understand, many other Scandinavians).


> However, contrary to what I suspect many of you might be thinking,
> that doesn't mean that they see a black and white world.  They can
> make color discriminations just not the same ones that humans make.

If I remember correctly, some of the older studies that suggested that
mammals (cats, in particular) were completely colorblind did not control
adequately for differences in intensity in their color samples.  The cats,
which have more rods than we do, latched on to the slight differences in
brightness rather than paying attention to the color differences.  More
recent studies indicate that many mammals do in fact see in red (well,
technically yellow) and blue, like me :-).


> To titillate just a little, my conclusion based on what can be
> inferred from the molecular biology of extant animals: if you accept
> that horses are colorblind compared to humans then dinosaurs could
> have said with equal justification that humans are colorblind compared
> to them.

Right.  Many extant dinosaurs actually see in four colors (red, green,
blue, UV), correct?