> "Robert J. Chassell" <[EMAIL PROTECTED]> wrote: > > Deborah Harrell <[EMAIL PROTECTED]> wrote > > Horses actually do have color vision: they see > >blue and yellow (and grey). > That is very interesting. Keith should be able to > tell us what the evolutionary advantages are.
I couldn't find the nicely detailed article from before (had lots of charts and graphics), but this one reports "research [as of 1999] on color vision in farm animals shows that they are dichromats with cones (color sensitive retina cells) most sensitive to yellowish-green (552-555 nm) and blue purple light (444-445 nm)..." http://www.grandin.com/references/new.corral.html It also notes that pigs and cows have ~300 degree field-of vision, so I wasn't that off when I said horses have ~that. There is a diagram showing a cow's blind spot behind (they apparently don't have one in front, unlike horses), in a discussion of 'flight zones.' However, I did find a site that says horses have red-green vision, so perhaps we don't know as much as we think we do -- although they mention something about their method of testing for red/green discrimination as "estimated indirectly using the flicker photometric electroretinogram (ERG)," which could skew results. http://www.genetics.org/cgi/content/full/153/2/919 > In a `just so story' mode, I can tell you that > yellow the color of the > direct sun and therefore useful for determining > whether you are in > shade or not. Blue predominates in shade. > > Moreover, I presume that blue in association with > yellow enables you, > as a horse, to distingish among different shades of > green and > therefore among different qualities of grass. Both > sensor capabilities would cause those horses, or > proto-horses, that possessed > yellow/blue vision to reproduce better than those > which lacked them. Horses can definitely recognize a patch of their favorite grass from a distance of at least 20 yards - I can see a color difference (type of blue fescue), so I'd guess that they can too, although it could smell different as well. > Is there any evidence that this `just so story' is > true? What are the alternative possibilities? That other grazing animals have this same type of color vision (assuming the first site cited above is correct) would certainly point to an evolutionary advantage -- after all, how else to describe the great green-grey Limpopo River (IIRC)?. ;) This speaks about predator vs. prey animals' reactions to novel or moving things: "...In research on the brain, they�ve shown that the emotion center is hooked up in such a way that rapid movement can still activate a fear response in a prey species animal. What does it make a predator do? It makes a dog chase. They do just the opposite. This little dog here (on the slide), she chased anything that moves. And the horses, they are going to want to move away from things that move rapidly, unless they get habituated. It�s possible to habituate a horse to specific things they haven�t seen before that moves rapidly. That is much more likely to spook them than something that makes a steady movement like this that doesn�t tend to activate the nervous system..." http://www.horsemensvoice.com/grandin/ And I'll add that while horses are poor at generalized thinking ("My dark fuzzy blanket isn't scary. This shiny crinkley thing...is a blanket. So it is not scary." Actual reaction: "This Thing Has Trapped Parts Of Horses! (reflections) Run for Your Life!!!!"), they are able to do a limited amount of it, if they have been carefully exposed to many new situations. Really scary or painful things/situations can unfortunately be generalized very quickly (trailers, people in white lab coats, and so forth). Debbi Furry Happy Monsters Feeling Glad Maru ;) __________________________________ Do you Yahoo!? New and Improved Yahoo! Mail - 100MB free storage! http://promotions.yahoo.com/new_mail _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
