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So, I understand that human skin color is based on the distance from the equator, but would it be possible to evolve skin to be a non-natural color such as green, pink, blue, purple, ect? Perhaps if it would not be possible on Earth, would it be possible on another planet with a different climate? What gives skin pigment, anyway? Does blood alter the color of skin? Does our red blood make us look pink? I'm sorry, that's a bit off track. Help?

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  • $\begingroup$ FYI: some people on earth already develop pink skin. $\endgroup$ – Aify Jul 20 '15 at 19:42
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    $\begingroup$ For evolution of blue skin: en.wikipedia.org/wiki/Blue_Fugates $\endgroup$ – Nathan Merrill Jul 20 '15 at 19:42
  • $\begingroup$ The question is not how, but why. As to the answer, I have no idea, but I'm sure it's possible. $\endgroup$ – DaaaahWhoosh Jul 20 '15 at 20:07
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    $\begingroup$ Since some animals have blue skin, it is obviously possible to evolve it. See e.g. the western fence lizard, commonly known as the bluebelly lizard: en.wikipedia.org/wiki/Western_fence_lizard#Identification Some mammals also have areas of blue skin: yale.edu/opa/arc-ybc/v32.n30/story15.html $\endgroup$ – jamesqf Jul 20 '15 at 23:53
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    $\begingroup$ Why? A big rapid change can be a feedback of sexual preference. Blue skin, like breasts, would take off if it was found to be desirable in a mate, esp. during the period when humans were splitting off from chimps. $\endgroup$ – JDługosz Jul 21 '15 at 9:08
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Skin colour in humans is affected by three main sources: blood, melanin, and the skin cells themselves.

In the absence of the first two, skin is generally a yellow-white colour; this is the least likely to change (assuming something close to normal human biology), but also the least important. It's not a particularly intense colour, so it's easy for other things to overpower it.

Human blood is primarily coloured by the hemoglobin in our red blood cells. This is based on ferrous iron (Fe2+), giving the classic red colour. There are other options here; changing some of the iron in the hemoglobin to ferric iron (Fe3+) makes the blood (and therefore skin) appear blueish - unfortunately it does that by making it less effective at transporting oxygen, so while this does occasionally happen in individuals, it is highly unlikely to ever become widespread in the population.

Moving to more exotic options, some other species use hemocyanin instead of hemoglobin, which gives them blue blood. In pale-skinned humans, this would lead to a blueish skin colour instead of the normal pink. Changing the oxygen-transporting molecule used in the bloodstream is a major change to bodily function, though; it would be plausible as a result of genetic engineering, but not natural evolution.

Finally, most 'normal' variation in human skin colouring is due to variations in melanin concentration. This is a pigment which essentially exists solely to colour skin, for the purpose of protecting us against damage from UV light. This is the most likely way that other skin colours would evolve - humans already have multiple forms of melanin with different colours (red/blonde/black hair all get their colour from it in one way or another), and similar chemicals in other species have different colours again (particularly relevant to the question is squid ink, which is coloured by melanin and is blue-black). It would be perfectly plausible for some group of humans to develop a different skin colour due to a change in how their melanocytes function - possibly due to a change in diet and/or environmental pressure, or possibly due to a random mutation.

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    $\begingroup$ To elaborate: Oxygen transport molecules using other metals (e.g. copper and chrome) are much less efficient at transporting oxygen to the critter's tissues. Something like $\frac{1}{4}$ as effective. $\endgroup$ – Jim2B Jul 21 '15 at 1:59
  • $\begingroup$ Most of this would be a case of an evolutionary "You can't get there from here" problem. Human blood is pre-selected, and a change so drastic as to use a different oxygen transport molecule would be more lethal than revolutionary. $\endgroup$ – Monty Wild Jul 21 '15 at 2:06
  • $\begingroup$ Would it be feasible to evolve less efficient oxygen transporting capabilities if a modern day human would live in an environment with a higher oxygen concentration? As far as i understood evolution, anything can develop as long as it does not hinder the creature. Add some sexual attractiveness for selection, and it might work out? Or is that jsut my poor knowledge of biology? $\endgroup$ – Burki Jul 21 '15 at 9:31
  • $\begingroup$ Very few things are 100% impossible, but it's still not likely. Higher oxygen concentrations would potentially allow blood to get less efficient at transporting oxygen... but they'd also mean that it stays red for longer. Blue blood is basically a sign that your blood isn't efficient enough for the environment you're in. (And switching from iron to another metal without the species going extinct in the process would be ... difficult.) Sexual attractiveness is probably going to work against the change - it's usually a signal of fitness, and inefficient blood doesn't qualify. $\endgroup$ – Toby Y. Jul 21 '15 at 9:59
  • $\begingroup$ Monty Wild and Toby Y - the op doesn't specify the skin color of humans, and talks about both Earth and other planets. The op presumably asks about the skin color of both animals and intelligent beings evolved both on Earth and on other planets. You don't have to assume a possibly extraterrestrial species has Earth like blood to switch from in the first place. $\endgroup$ – M. A. Golding Jan 22 '18 at 15:07
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Skin color in humans is normally determined by the concentration of the pigment melanin in the skin. The genes of albinos prevent the synthesis of melanin, which means that their skin itself contains no pigment. Thus, they are very pale, except where their blood shows through the skin, in which case they may appear pink.

People may develop blue skin through a variety of medical disorders, such as cyanosis. They may also become blue because they consume silver orally, by way of a quack medicine called "colloidal silver", whose effects are demonstrated in the picture linked below. Apparently, this condition is called "argyria".

http://i.imgur.com/WFdXIFi.jpg

Thus, perhaps some species could evolve the ability to consume silver to make their skin blue. The most obvious advantage for such an adaptation would be for camouflage, assuming that some part the species' environment (the sky?) is a similar color.

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  • $\begingroup$ Do you have a source for that image? $\endgroup$ – Frostfyre Jul 20 '15 at 20:42
  • $\begingroup$ I did a Google image search for "colloidal silver". It's included in a story on Reddit, at the URL "reddit.com/r/creepy/comments/2x88nu/…". The URL of the image itself is "i.imgur.com/WFdXIFi.jpg". I gather that it may originally be from the television show "Oprah". Sorry if it falls afoul of some copyright rule--I'd be happy to delete it if so. $\endgroup$ – Doug Warren Jul 20 '15 at 20:46
  • $\begingroup$ I went ahead and replaced the inline image with a link. $\endgroup$ – Doug Warren Jul 20 '15 at 20:54
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Most of the answers so far have concentrated on the biological processes that contribute to the our perception of skin colour.

An alternative approach might be to look at how the human eye might evolve to interpret optical light differently.

Our eyes and brains currently interpret a certain range of frequencies in the optical light spectrum as possessing colours. If our eyes were to evolve so that a gradual shift in the range of frequencies we perceive were to take place, then what we perceive as natural skin colour today could in the future be interpreted as blue.

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When we are exposed to too much silver dust, or injest too much colloidal silver, our skin actually does turn blue - it's called argyrosis. I'm not completely sure of the medical implications of the condition, but apparently it damages the rods in your eyes, and your kidneys.

If you had a population of people that lived off a food source rich in silver (for whatever reasons) they would definitely be blue. Add a little bit of genetic resistance to the more damaging aspects of silver, and voilà! Blue (or purple) people! It's just like how pink flamingoes are only that colour because of their diet!

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I may be wrong but I think plants have evolved to be green because green is the opposite colour to the light they receive from the sun. This means they absorb the most light possible.

As you didn't specify if the skin had to belong to a human, one could suppose that if an animal on a planet orbiting a red dwarf needed some way of converting its stars light to energy in its skin, their skin would be blue.

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    $\begingroup$ Plants that are green are green because they reflect more green light. The chloroplasts absorb blue and red light more effectively. By doing so, they fail to use a large portion of the incoming sunlight. Sunlight is white because is contains the full spectrum of colors of light (plus UV and infrared) $\endgroup$ – Gary Walker Jul 21 '15 at 10:41
  • $\begingroup$ I don't think red dwarf stars are literally red... and the opposite of blue is yellow! $\endgroup$ – colmde Jul 21 '15 at 11:04
  • $\begingroup$ @colmde the opposite of blue is actually orange, i.e the mixture of the other two primary colours, in this case red and yellow. And, red dwarfs (often) are red. That's what gave them their name. A quick google search will provide pictures. $\endgroup$ – Burki Jul 21 '15 at 12:13
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Perhaps spending a lot of time at sea would cause it to do so, as it would blend in with the sea color and serve as camouflage. Cetaceans evolved from land animals, and their skin is blue.

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Photosynthesis. Some forms of chlorophyll are coloured blue. So they evolved to get a daylight energy top up from the sun.

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Blue skin would be skin that reflected a lot of blue light. So perhaps we'd have blue skin if our environment exposed us to enough blue-wavelength light for it to be damaging, and our skin developed ways of reflecting it.

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