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I have been designing a species of elves with blue skin as one of their most striking features. I'm drawing inspiration from primates that also have blue skin. Think the scrotum of a vervet monkey, or the buttocks of the mandrill. According to this article,(http://jeb.biologists.org/content/207/12/2157.full), the color is caused by light scattering through special layers of collagen. This layer can be 800-1500 micrometers (0.8-1.5 mm) in the areas described.

As an adaptation to produce and support this amount of collagen, I'm giving the ability to synthesize their own vitamin C, a somewhat carnivorous diet, and a higher haemoglobin count to improve oxidation to the dermis. I'm considering having them sail and hunt in the ocean, since they would be effectively immune to scurvy.

However, Human skin ranges from 0.5 to 4mm in thickness, so my hypothetical elves may have much thicker skin. My questions are follows: what impact would having this thick layer of collagen in the skin be on the elves everyday life? Could there be deleterious effects? And finally, are the adaptations I have listed enough to combat the potential problems?

Edit: as far as ’deleterious effects'go, the ones I can think of would be stiffness in the face and possibly a higher likelihood of forming scar tissue, though feel free to suggest more.

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    $\begingroup$ As I can gather from the movie Avatar, they seem to have no problem with your scenario. $\endgroup$ – Vylix Oct 5 '17 at 5:12
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    $\begingroup$ consider using blue blood (e.g. copper based as in horseshoe crabs) $\endgroup$ – JCRM Oct 5 '17 at 10:38
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    $\begingroup$ Not deleterious, so not adding as an answer: Collagen production decreases as you age, which is one reason old people have thin, wrinkly skin. This means that elf babies would be bluer and old people less blue. $\endgroup$ – G. Ann - SonarSource Team Oct 5 '17 at 12:19
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    $\begingroup$ An alternate method of blue skin (so a comment rather than an answer to your question) would be Argyria. Many varying worlds containing elves usually have them prefer silver (and mithril). Argyria results in skin turning purple or purple-grey and is caused by an excessive exposure to the element of Silver or Silver dust. $\endgroup$ – Michael Richardson Oct 5 '17 at 13:55
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    $\begingroup$ Your own numbers do not necessitate thickened skin, if you want further proof look at some of the species of blue faced monkey, even their eyelids are blue. i.pinimg.com/originals/fa/57/6e/… and c2.staticflickr.com/4/3004/3018420023_a0768ffe70.jpg $\endgroup$ – John Oct 5 '17 at 17:35
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The method you are proposing is already a human disease called scleroderma. It consists of excess collagen in the dermis (the soft tissue immediately under the epidermis, what we usually consider "skin"). Scleroderma leads to thickened skin, which will reduce flexion and can paradoxically increase skin fragility and cause poor healing. Most of the worst effects of scleroderma can be mitigated if the collage is ONLY in the dermis, not in internal organs.

This seems to be a complex way of approaching the goal of having blue skin. There are many pigments which can produce a blue color, just because few are found in current mammals doesn't mean that it can't happen. From an evolutionary perspective you just need a good reason for mammals to be blue and evolution will eventually select for that pigmentation.

Another option is that these blue elves engage in some sort of environmental contamination that gives them the blue color, much like how flamingos are pink only if they eat the correct food. In this case any elf sharing this part of their culture would be blue, and any blue elf denied that part may eventually lose the blue tint.

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    $\begingroup$ This "denied cultural communion" aspect would be a great way to recognize outcasts, thieves, &etc., $\endgroup$ – G. Ann - SonarSource Team Oct 5 '17 at 14:50
  • $\begingroup$ Thanks for the answer. Since it's the structure of the collagen that causes the color and not necessarily the amount, I may not make it too thick to minimize these issues. $\endgroup$ – Lot-Of-Malarkey Oct 9 '17 at 2:42
  • $\begingroup$ Blue skin is sexy. That's enough of a reason for it to evolve. $\endgroup$ – John Dvorak Oct 11 '17 at 15:08
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Human skin thickness is also a consequence of local wear. I remember reading somewhere the account of a castaway, who, after living years on a remote island and necessarily walking barefoot, had developed such a thick foot skin that he could walk on spiked rocks without the need for shoes.

The only problem I see is that the blue and thicker skin will also somehow affect the amount of UV radiation which can be used to produce vitamin D. And lack of vitamin D has important consequences.

This can be a limitation only if your elves live very far from the Equator, where the amount of light they can get is low.

EDIT: After Bret's comment, and considering you stated they live of fishing, lack of vitamin D is a minor issue.

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    $\begingroup$ perhaps They could be some sort of resource either animal or plant, that provides them with vitamin D $\endgroup$ – Bryan McClure Oct 5 '17 at 6:49
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    $\begingroup$ @BryanMcClure like milk $\endgroup$ – anon Oct 5 '17 at 13:08
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    $\begingroup$ @anon Milk is typically fortified with vitamin D. From a cursory Google search, only trace amounts of vitamin D are found in milk naturally. Fish and eggs would be a better bet. $\endgroup$ – Bret Oct 5 '17 at 13:40
  • $\begingroup$ Then it is no big deal, as OP specifies they live of fishing. $\endgroup$ – L.Dutch Oct 5 '17 at 14:14
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According to the linked article I can see that blue body parts have no hair or have very little of it. My guess is that this additional layer of collagen may somehow prevent hair follicles from appearing there.

Also, our skin's outer layer is basically dead cells. Cells from deeper levels of skin are constantly reproducing to restore the outer layer. For each dividing cell its "children" go upper and... die there, creating a protective keratin protein. If there is an additional collagen layer it may affect the restoration process. I believe that this blue skin will regenerate and renew itself at lower rates, it might become quite delicate and sensitive even though it's thicker, because there will be less of keratin.

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  • $\begingroup$ I had thought the lack of hair on the blue areas were sexually selected for because it made the blue color easier to see, but I could be wrong. However, since the thick collagen layer would likely be in the reticular dermis, which is al $\endgroup$ – Lot-Of-Malarkey Oct 5 '17 at 16:25
  • $\begingroup$ Sorry, technical problems. That last part was supposed to say that the collagen would be in the reticular dermis, which is where hair roots are, but the follicle is a part of the epidermis. So hair growth could be possible, but it would look short. $\endgroup$ – Lot-Of-Malarkey Oct 5 '17 at 16:39
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Skin that's too thick could present problems with temperature regulation. Blood vessels would be too far from the surface of the skin to lose heat effectively to the air. A way to circumvent this would be having your elves live in permanently cold climes so they wouldn't need to lose heat in the first place.

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  • $\begingroup$ Not necessarily. They could be just running on a lower metabolic rate, thus producing less waste heat. That would also conincide with a prolonged life span - as in, less wear and tear on the bodies. $\endgroup$ – Anonymous Feb 20 '18 at 9:00

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