Why do humans have brown skin?

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I’m not asking about dark or light. I’m asking why not shades of blue or green?

Bonus question: hypothetically, what factors could lead to other skin colors, like the aliens in avatar?

In: 18

Melanin is the pigment that evolved long ago in common ancestors of mammals that have melanocytes (cells that make melanin). And it is likely that color because it is the one that is best at absorbing the type of harmful radiation from the sun that causes damage to DNA.

It also is good for blending in with trees – a little bit of camouflage never hurts.

But the primary reason has to do with protecting against the harmful effects of the sun

Without melanin your skin and your hair would be white. Your eyes would be colorless so you could see the red bloodvessels.

Because the melanin is used to filter blue and UV-light the skin has a yellow/reddish or light beige tint. But for the production of Vitamine D a portion of blue/uv-light is used. So in region where the sun irradiation is high (equator zone) people have a darker or almost black tone. The downside for this people is that when they move to temperate zones usually have a Vitamine D deficiency. Light skinned people moving to the equator zone get a skin irritation(sun burn).

Mammals living in the sea (whales, dolphins) have usually a grey colored skin, while mammals living at the sea(seals) have usually a black skin.

Mammals on land have black or brown skin, even white horses. The only exception I can think of are albinoes (those with red eyes).

the reason flesh color is flesh color is that it’s the white of the skin, combined with the squishy red tissue underneath, in what we call the dermis.
So we got something called melanocytes, which is at the bottom of your skin, or epidermis, this produces something called melanin, and melanin does one thing when produced, which is darken the skin above, which causes a brown color and eventually black color.
But why not Green? Why not Blue? We got green eyes, we got blue eyes!
Answer here is simple. well, im lying, cause it’s not.
Now the reason we got colored eyes, is this cool thing called the stroma, which is a set of cool ass fibres/tissue thing, and either it or behind it has the gnarly melotonin that gives it the color, but it also contains a fluid that changes the light so that the light reflected back gives you non-brown eye colors.
While humans have loads of fluid, there is no turbidity in the skin to change the color, much like a prism would.

To get other skin colours you would need a different coloured pigment other than melanin. The gene for a different coloured pigment is unlikely to turn up spontaneously. So we could start growing algae on our skin like sloths (green pigment in algae is chlorophyll) or genetically engineer ourselves to produce different coloured pigments in our skin. Like green fluorescent protein. Then we could glow in the dark too!

Blue can and does happen. Not only is it prevalent in many ancient cultures such as India, there are also noted families in the US.

The Fugates, a family who lived in the hills of Kentucky, commonly known as the “Blue Fugates” or the “Blue People of Kentucky”, are notable for having been carriers of a genetic trait that led to the blood disorder methemoglobinemia, which causes the appearance of blue-tinged skin.

Make it short for ya:

In africa / high sunlight exposure places people needed melanin to not get sunburnt.

When they went further north, there was less sunlight, so they evolved brighter skin to catch more sunlight to get enough vitamin D

This was a much more wholesome thread than I expected it to be. Thank you ♥️🤘🏾

I can tell you why humans aren’t green. There aren’t many green animals with lifespans that exceed the spring/summer season simply because when it becomes winter, a large green animal would be easier to see due to a lot of the greenery/foliage being dead/dormant. That’s why you don’t see mammals with green fur. Typically mammals have black, gray, brown, or neutral colored fur.
In contrast, many insects are green colored, because they die in the winter season, so they don’t have to worry about camoflauge during winter.

I would also guess that humans aren’t blue for the same reason.