Evolution of Skin Color

Ever wondered why there's this much variation in skin color?
I will share my insight and hypothesis...

Common Skin color of haired mammals is pale.
After Ice age due to rise in temperature,
when human beings started shedding body hair to facilitate sweating,
diversification of skin tone occurred.
Evolutionary pressure from various sides lead to the current spectrum of skin tones.

Humanity originated in Africa and migrated to other continents.
During this migration there was gene flow between these isolated groups (they had sex).
This further complicated the evolution of skin color.

Pale skin tone was superior in Temperate zone.
Why?

Vitamin D is the key.

Pregnant women need lot of vitamin D for Skeletal Maturation of fetus.
So Dark skinned mothers in Temperate zone had fetuses with
Skeletal defects and gradually became extinct.

You can see this if u compare skin tone of men and women of same ethnicity.
In general, Women have paler skin tone than men due to increased requirement of vit D.

Testosterone makes skin tone darker.
Dark skin is superior for men as in course of evolution,
they spent their time outside in sun hunting and gathering food.
So dark skin gives protection from uv.

Dark skin tone is Superior in Tropics.
Why?
This perplexed researchers for a long time.
The reason for this was only discovered recently.

Folic Acid is the key.

Pregnant women need lots of folic acid.
Folic acid is a fragile vitamin.
It is easily destroyed by UV-A rays in sunlight.
So pale skinned women in tropics,
gave birth to babies with neural tube defects
and they gradually became extinct.

Another important factor is Sexual Selection.
Mating Preference of women for men with specific features further complicated this.

In India, a caste system existed.
People of higher caste, were not working outside,
so their skin tone was pale.
Lower caste worked outside in intense sun.
So they had dark skin tone.
So Dark skin became less preferable.

But from an Evolutionary Standpoint,
Dark skin is an advanced trait...