Why no blue or green fur?

Discussion in 'Biology & Genetics' started by Dinosaur, Nov 17, 2003.

  1. Dinosaur Rational Skeptic Valued Senior Member

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    It occurred to me recently that no animals have blue or green fur. Why not? There are animals with fur in various shades of red, orange, yellow, tan, brown, gray, white, black.

    I suppose that animal biochemistry is capable of creating blue or green fur. There seems to be no limit to the colors possible for birds, butterflies, and flowers. Is there no evolutionary advantage to these colors? Green seems like wonderful camouflage for an animal who lives in a jungle, forest, or a green meadow.

    Is there anybody here with a knowledge of biochemistry who might be able to tell me if blue or green fur is possible? Is there any evolutionary reason why these colors do not occur?
     
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  3. scilosopher Registered Senior Member

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    That's an interesting question ... and since people have green and blue eyes there is certainly no reason to think we couldn't fairly easily make those color pigments by some evolutionary quirk.

    As they also occur in fish, which are typically much more sheltered from light and UV, and also are the colors of choice for grabbing light energy bly plants and other photosynthetic organisms, it would seem possible that it has something to do with the absorbtion of heat and reflection.

    Polar bears are white because it helps absorb heat best (you reflect the light deeper into the coat and therefore actually increase heat absorbed by the body). Black fur is often used to actually keep heat absorbtion down (it heats the surface of the coat, but is radiated away). Maybe greens and blues are intermediate in a not so useful way.

    Maybe not though it's just a thought.
     
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  5. Idle Mind What the hell, man? Valued Senior Member

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    Scilosopher, I think you are a little mixed up here...Greens are not favoured by plants. Plants are green because they reflect green light. Since it is relfected, it is not absorbed, and thus, it isn't used.

    Also, white reflects light of all wavelengths (white light = all colours of rainbow). Black absorbs all wavelengths of visible light, and doesn't relfect any. Try sitting out in the sun in a black shirt, and tell me it doesn't absorb light.
     
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  7. Dr Lou Natic Unnecessary Surgeon Registered Senior Member

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    I think polar bear fur is actually transparent or something to get the suns rays to their black skin.
     
  8. curioucity Unbelievable and odd Registered Senior Member

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    Hmm, right...... even though some mammals live on green prairie, why don't they have green fur? We know that green surfac is common in birds, frogs insects etc, but why not mammals?
    I think I have one theory here: Grouping is considered more important than camouflage by high-level animals (mammals, birds), so they'd rather look clearly large rather than faintly visible. Okay, some grouping birds maybe green, so hit me.
     
  9. spuriousmonkey Banned Banned

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    The sloth has green fur, because of the algae that live in it. The colour actually changes with the seasons.
     
  10. scilosopher Registered Senior Member

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    I know the colors absorbed are the complement of that which you see, but one can speak in either coordinate set (and previously it was clear that percieved colors were being used), they're equivalent if you have a broad incoming spectrum like sunlight.

    I know black absorbs all light, but think of the bedouins that wear black cloth. If you have multiple layers or a relatively thick covering like fur, it works quite well to have the surface get hot where it's easily convected away (I did mispeak when I said radiated, the main loss is through convection).

    Polar bears have white fur, which makes the sunlight reflect along their hairs to their skin. If the fur was translucent they would look darker. They are one example of white being used to increase absorbed light (though I should have mentioned the black skin).

    It is certainly possible that there are schemes where other color/fur/skin arrangements are better, but theoretically I think those two are almost the best you can do. In the case of polar bears there is also a definite advantage of white for camoflage.

    Anyways it was certainly hand waving, but I wasn't terribly confused.

    That's cool that sloths have things growing on them and change colour. I wonder why they use that approach to be green. Reptiles frequently have green skin and birds green feathers, which are both examples of green being an adaptive trait for color, but not used for fur. Interesting. Basically everything except furry animals have natural green covering in green environments.

    It could have something to do with the biosyntheitc pathway used in hair pigmentation and it being tough to make green/blue from the molecules involved, but I think it's unlikely in my gut..
     
  11. BigBlueHead Great Tealnoggin! Registered Senior Member

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    I'm not sure that an animal that moves so slowly that it gets moldy is really the same as a parrot that grows green feathers...
     
  12. Clockwood You Forgot Poland Registered Senior Member

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    I would guess that all mammals evolved from a common ancestor that had the genes to produce only a few types of pigments, not including blues or greens. As browns and blacks were sufficent to let the mammals blend in (after all, most vertibrates are colorblind) there was little real benifit to evolve new pigments most of the time. The status quo was maintained.
     
  13. curioucity Unbelievable and odd Registered Senior Member

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    Oh, yeah, right... I forgot the fact that most mammals are colorblind...... While in the other hand birds can see as many colors as we can.
    But wait, if the thread starts with furs, I shouldn't have included birds etc... my bad....
     
  14. weebee Registered Senior Member

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    I think that the quantities of pigment needed to produce green and blue fur would be toxic as by products to the mammalian liver.

    BTW there are some lizards that have green blood (biliverdin-type pigment, similar to that found in bile). They have amounts which would be toxic to us, hence my theory.

    Someone asked the same question on a different site;
    http://www.madsci.org/posts/archives/jul99/931597764.Gb.r.html
     
  15. BigBlueHead Great Tealnoggin! Registered Senior Member

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    Good call, never thought of that.

    Fact is, there are even a lot of plants that don't have any blue expression in them, despite being green. They're having a hell of a time breeding blue roses. (Right now the only "blue" roses they have are pink.)
    Plants that express blue colours require a lower than usual soil PH to be able to create the blue pigment (things like blueberries, for instance, grow in swamps where the soil is acidic). Just as much of the plant kingdom doesn't express these blue pigments, it may be that the mammals are on the luckless side of the evolutionary tree that didn't get the cool colours.

    Otherwise we'd probably have green wolves. That would be pretty impressive.
     
  16. BigBlueHead Great Tealnoggin! Registered Senior Member

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    Sci said:
    Yeah, each individual hair is actually a tube... the reason why some polar bears look yellowish is because algae grows inside their hair and changes their colour as well.

    I don't know if this provides a symbiotic benefit or not; I assume that algae are more like land barnacles, organisms that offer no benefit but also represent little cost.

    Many animals shed their fur seasonally, so they could be green in the summer and white in the winter.
     
  17. ElectricFetus Sanity going, going, gone Valued Senior Member

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    Pigments are limited in most mammels because they never evovle colors like Green and blue, some mammals do have those colors though but as of yet none have evolved means of incorporating them into hair. This is simply luck as birds have evolve these pigments and incorporate them into feathers. Biochemcially I can not think of reason why blue and green pigments can not be found in hair. Feathers, scales (fingernails) and hair are made of beta or alpha keratin, these keratins have little biochemical difference in primary and secondary structure, Only in quaternary structure (protein aggregation: hair is a fiber, fingernails are sheets) do these protein really differ. Mammals also have the pigments needed or at least the necessary archea types pigments that have with some small sequence changes been evolve in other classes (birds, reptiles, ect) to be blue, green and violet.
     
  18. spookz Banned Banned

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    fascinating.
    i am stumped and frustrated
    it seems too much of a coincidence that a random mutation did not result in the colors mentioned. perhaps there is a reason.( there really doesnt have to be one)
     
  19. pilpaX amateur-science.com Registered Senior Member

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  20. weebee Registered Senior Member

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    Not sure about this but quite a few internet sites say that birds don’t produce blue, and in many cases green pigment, instead its all due to structural pigments –light diffraction ext. http://www.stanfordalumni.org/birdsite/text/essays/Color_of_Birds.html The common example of being what you eat, is flamingos which are pink because of their diet (small crustaceans and algae)

    But how would you go about producing a blue/green mammal. Eumelanins that produce a brown-black colouration; and phaeomelanins that produce yellow-red colouration don’t mix to produce green/blue. The starting point would be one of the porphyrins, the turacoverdin which birds do have, say the sites so they are contradicting themselves (only turacos have this pigment). Looking up porphyrins I found; Porphyria is a group of inherited disorders involving abnormalities in the production of heme pigments (the base material responsible for hemoglobin (red blood cell pigment), myoglobin (reddish muscle cell pigment) and another group of materials called cytochromes. Porphyrias are characterized by three major findings: photodermatitis (light sensitivity causing rashes), neuropsychiatric complaints, and visceral complaints (such as abdominal pain or cramping). So maybe the reason we don’t use porphyrins as pigments is because of the other biological roles the ‘base’ pigments play in mammalian bodies. So a mutation in a pathway may effect the blood before it effects the hair colour….I’d still say the major reason is the lack of evolutionary ‘push’.

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  21. ElectricFetus Sanity going, going, gone Valued Senior Member

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    Hahahaha

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    porphyrins hold metal ions which allow them to take on so many colors (they are the key to a heme group on a proteins), for example your blood is red because of the iron the hemoglobin in your blood holds thanks to porphyrins. Porphyrins can hold a variety of metals and every color in the rainbow. From the green manganese heme group of plant chlorophyll, to the red iron of blood, to blue copper-based porphyrin, ect.
     
  22. one_raven God is a Chinese Whisper Valued Senior Member

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    From what I have learned, Polar Bear fur is transparent and hollow.
    Transparent for the reason Lou stated and hollow because the individual hollow tubes make an excellent insulator to KEEP the black skin warm.

    I could have very well been misinformed, however.
    I will look it up and see what I can come up with (if I remember to).
     
  23. Dr Lou Natic Unnecessary Surgeon Registered Senior Member

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    Yes thats what I forgot they are hollow as well.
    I think we are correct one raven.
    I'd like to say I just knew this from being a mastermind on the subject of animals but I only learned it recently.
    I'm fairly confident it is correct though.

    I agree with clockwood that the ancestor to all mammals probably by chance didn't happen to have blue or green potential.
    But at the same time I think it would have happened if it had to, it just hasn't needed to yet.
    Some breeds of dog are almost blue and a hundred years of selectively breeding for blueness alone would undoubtedly leave us with some fairly blue individuals.
    Maybe not marge simpson hair colour though, that might take a thousand years or more, or for all I know it might be impossible for some reason. Not sure.
     

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