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There are a number of animals that can change color in a short time, like some chameleons and octopuses.

Is there any reasonable way for a color-changing mammal to evolve naturally?

I'm looking to end up with a mammal that can change its color in a matter of minutes, not months. This mammal would use its camoflage to help it hunt and to hide from dangerous predators.

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    $\begingroup$ Embarrased humans? $\endgroup$ – jamesqf Apr 1 '17 at 5:11
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If your mammal is hairless then there is no fundamental problem -- for example it can evolve a mechanism to produce and absorb certain pigments in the cells of the basal layer of the epidermis, or it can have a population of mobile pigmented cells in the dermis. With hair or fur things get complicated because hair is not living tissue and its color cannot be changed once it has grown; you may imagine a fur made up of two or more kinds of different colored hairs (sort-of like roan horses) with color change being effected by sets of arrector pili muscles.

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  • $\begingroup$ There is one way hair could be used, sloths have symbiotic bacteria and fungi that live in their hair, they could change color, the issue is whether there is a way the sloth could control it. $\endgroup$ – John Apr 1 '17 at 15:59
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No, but for a technicality: animals that developed this ability would probably become a new category.

If some creature loses its mammalian hair and develops a new type of skin covering, that would be a major trait noticed even by pre-scientific naming. Birds have feathers, mammals have hair, and has photo active skin covering.

What drove this change would be major evolutionary pressures, so it would not be the only change. It would be different in many ways, and it might only be through modern studies that the accurate determination was made that branched off mammals, some millions of years ago.

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  • $\begingroup$ Is the new category really unavoidable? Or even likely? Humans are still primates, and chameleons are still lizards. $\endgroup$ – avek Apr 1 '17 at 3:05
  • $\begingroup$ Humans are more like other primates than most people realize. I think the color changing animal would become different and diverge in many ways over the millions of years it takes to evolve this ability. $\endgroup$ – JDługosz Apr 1 '17 at 9:58
  • $\begingroup$ Mammals are a monophyletic clade, meaning that any descendant of the original mammal ancestor is considered a mammal as well. In practice all living mammals have some hair, but some mammals are near-hairless (whales and naked mole rats for example) and even if they lacked hair entirely they would still be considered mammals, since they belong to the same clade. One might argue that if there were a mammal that didn't produce milk it would prompt a name change for the entire clade (mammal = mammary), but this has more to do with human naming conventions than actual physical reality. $\endgroup$ – IndigoFenix Apr 2 '17 at 6:21
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Two-toned Strobe Beast

Here is a fictional color changing animal that is reasonable and not too far from a standard mammal plan. Start with a porcupine.enter image description here

enter image description here

Some quills are strikingly two-toned. https://www.objectlessons.org/natural-world-earth/porcupine-quills/s89/a374/

The Strobe beast has two toned quills also, but longitudinally. Half is black and half is white, like this dog's claws.

enter image description here Poodleforum.com

Porcupine quills are modified hairs. They are mobile and the porcupine can raise and lower them. The Strobe beast does not raise or lower, but can rotate its short two-tone quills 180 degrees, like a human wrist or head. The short quills lie flat along the body.

Quills can rotate from black side up to white side up and back in a split second: thus the name "strobe beast". The beast can be black or white or shades of gray. It could be, if it chose, two toned like a tapir.

If you allow more precise control of stretches of quills the strobe beast could make circumferential rings and patches like this genet. enter image description here from robertharding.com

Not only could it have patterns it could make the patterns move. The strobe beast could make circumferential rings of black and white move along its body. A creature with contrasting rings moving along its body would be very confusing to watch. It would be hard to tell which direction the creature was moving. A black strobe beast could lie still and move a patch of white back and forth along its body, drawing in small predators in the manner of an angler fish and then catching and eating them.

The strobe beast cannot turn green or magenta. Just black and white and combinations.

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It's plausible: after all, color changing ability has evolved multiple times and with different mechanisms. It could even be argued that humans have a degree of color-changing ability - we slowly make our skin darker in response to sunlight, and can quickly turn red when angry or embarrassed by expanding blood vessels near the skin (the latter may even be a form of social signalling).

Mandrills are famous for their various colors, with patches of blue and red on their faces and buttocks, and various shades of purple in between. They accomplish this through a combination of light-scattering collagen fibers and the swelling of blood vessels near the skin. These mechanisms are controlled chemically, through testosterone, but they could plausibly be controlled directly through muscle contractions (perhaps the same muscles responsible for making hair raise up could stretch or squeeze the blue parts, and the red could be controlled through the same mechanisms that allow humans to blush). This would allow a mandrill descendant to shift its color patches at will. There is an evolutionary benefit to this: male mandrills normally change their color slowly over time in response to social status; a brightly-colored mandrill has more access to mates, but this also incites challenges from competing males. A weaker male with color changing abilities could "cheat" by turning more brightly colored when around females and then becoming dull-colored when the competition shows up.

A possibility that would work with a hairy mammal could be to grow multiple colors of hair close together, and have the muscles for raising each color hair respond to a different trigger. Raised hairs would stand out over lowered ones, so (for example) the animal could appear red by raising all of its red hairs and letting the other hairs lie flat. By mixing combinations of red, black, and white, the animal could flash through the entire spectrum of colors available to mammalian hair.

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