What determines skin tone?

Heredity and melatonin.

Melanin

It’s polygenic process.

Recalling elective 500-level biology class: I think there’s genes on chromosomes 1, 2, 4 and 15 that determine skin colour. Please correct me, bio-geeks, if I’m wrong.

Vitamin D. The further north human beings migrated, the more they had to lose their natural skin tone so that in the relatively dim Northern light they could still manufacture sufficient vitamin d.

If I had to guess, I would probably say its a combo of the sun, genetics and what you eat during the evolutionary process. Like in Japan. A tall person was rare, but as they mingled with western culture they are taller. If you look into cultures that eat primarily fish in their diet they tend to be smaller and your meat eaters are larger. It could just be a coincidence.

alleles

Quote:

Synthesis in the skin involves UVB radiation, which effectively penetrates only the epidermal layers of skin. While 7-dehydrocholesterol absorbs UV light at wavelengths between 270–300 nm, optimal synthesis occurs in a narrow band of UVB spectra between 295–300 nm. Peak isomerization is found at 297 nm. This narrow segment is sometimes referred to as D-UV.[14] The two most important factors that govern the generation of pre-vitamin D3 are the quantity (intensity) and quality (appropriate wavelength) of the UVB irradiation reaching the 7-dehydrocholesterol deep in the stratum basale and stratum spinosum.[13]

A critical determinant of vitamin D3 production in the skin is the presence and concentration of melanin. Melanin functions as a light filter in the skin, and therefore the concentration of melanin in the skin is related to the ability of UVB light to penetrate the epidermal strata and reach the 7-dehydrocholesterol-containing stratum basale and stratum spinosum. Under normal circumstances, ample quantities of 7-dehydrocholesterol (about 25–50 µg/cm² of skin) are available in the stratum spinosum and stratum basale of the skin to meet the body’s vitamin D requirements,[13] and melanin content does not alter the amount of vitamin D that can be produced.[21] Thus, individuals with higher skin melanin content will simply require more time in sunlight to produce the same amount of vitamin D as individuals with lower melanin content. The amount of time an individual requires to produce a given amount of vitamin D may also depend upon the person’s distance from the equator and on the season of the year.

Source

It’s a combination of melanin, skin exposure, vitamin intake, etc. Of course the main factor would be that genetically inherited melatonin. Everyone is born with the same amount of it, but it is simply more active in some people based on their heritage, and environment.

Melatonin and I agree with @dpworkin. I would blame evolution.

melanin. melatonin regulates your circadian rhythms

Thanks. Of course you are correct. I’m too tired to be doing this, it’s almost midnight.

Thnks all, I knew there was a logical reason for this that I just couldn’t think of!

Protection from sunlight. So darker skin in hotter climates is better.