Dermal Melanin Selection

[CDarwin]

That was the most intelligent-sounding name I could think of for something that's likely a fairly stupid question.

 

Is skin color selected for all at once all over the body, or is each melanocyte individually subject to selection? I'm essentially just asking how the genes that determine mammalian skin color work. Feel free to patronize.

[CharonY]

The selective advantage or disadvantage (aka fitness modification)is conferred to the whole organism, as melanocytes cannot propagate outside the organism.

[CDarwin]

Conferred yes, I understand that. My question is whether selection is for genes that control skin color all over the body or on each melanocyte.

[lucaspa]

That was the most intelligent-sounding name I could think of for something that's likely a fairly stupid question.

 

Is skin color selected for all at once all over the body, or is each melanocyte individually subject to selection? I'm essentially just asking how the genes that determine mammalian skin color work. Feel free to patronize.

 

A bit of both. In development all melanocytes derive from the ectodermal layer, but there can be distinctions between different areas of the skin. For instance, in humans those with darker skin usually have lighter skin on the palms of their hands.

 

This is going to depend on when and how long certain genes are expressed during development. And this in turn depends on transcription factors, which are products of other genes. So, there can be two forms of a transcription factor. One is active in one area of skin and another active in a second area.

 

BTW, skin color in humans is a balancing act between competing selection pressures:

1. Dark skin to protect from UV light which destroys folic acid. Too much sun depletes folic acid, which results in neural tube defects during embryogenesis.

2. UV light is needed to make vitamin D. Vitamin D isn't really a vitamin, but is made by the action of UV light on cholesterol in the skin. Too little vitamin D and the result is rickets. So need lighter skin in weak sun to ensure enough vitamin D.

1 G Kirchwager, Black and white: the biology of skin color. Discover 22: 32-33, Feb. 2001.