What were the evolutionary advantages that formed (sociological) races?

[Firedragon52]

We all know why humans initially had darker skin. (Protection from the sun.)

 

What are the other possible advantages, that came from migrating to a new environment, that caused the physical differences among races?

 

Why do some races have curly hair while others have straight hair?

 

Why do asians have slightly "slanted" eyes?

 

Why do caucasians and asians have slightly different skin tones (Both left Africa, why the change in skin tone?)

 

What were the evolutionary advantages of the diversity?

[Thales]

Curly hair is usually shorter and covers less area of skin resulting in easier heat disipation.

 

Slimmer eyes makes it easy to see in glary and/or windswept areas.

 

Skin tone is more a bit more difficult but i should imagine it has to do with the amount and intensity of sunlight recieved in the varying environments.

[Firedragon52]

Slimmer eyes makes it easy to see in glary and/or windswept areas.

Are the regions of Asia brighter and more windswept than other regions of the world?

[Thales]

Lots of snow and deserts. That whole area is pretty much the most 'inland' you can get in the world so while I'm no meterologist I would assume so.

[Firedragon52]

Thales, does your answer come from sources or is it just a guess?

[Thales]

The first one is just common sense. The second and thrid are educated guesses based on facts I have gathered over the years but I have no specific reference. Makes sense to me.

[coquina]

PBS has a very interesting article on their website:

 

http://www.pbs.org/wgbh/evolution/library/07/3/text_pop/l_073_04.html

 

Snippets of information from the article:

Their findings, published in a recent issue of the Journal of Human Evolution, show a strong, somewhat predictable correlation between skin color and the strength of sunlight across the globe. But they also show a deeper, more surprising process at work: Skin color, they say, is largely a matter of vitamins.

 

 

Paraphrasing: The earliest humans probably had a lot of body hair, like chimpanzees. They probably only had sweat glands on their hands and feet. When humans started foraging on the savannas, primates with hairless bodies and lots of sweatglands were best able to survive the heat.

 

Hairless, pale skin, is most easily damaged by ultraviolet light. Melanin is a natural protector against ultraviolet light absorption. Although UV light can cause skin cancer - this usually happens late enough in life that it doesn't interfere with reproduction.

 

An hour of intense sunlight, the study showed, is enough to cut folate levels in half if your skin is light. Jablonski made the next, crucial connection only a few weeks later. At a seminar on embryonic development, she heard that low folate levels are correlated with neural-tube defects such as spina bifida and anencephaly, in which infants are born without a full brain or spinal cord.

 

Jablonski later came across three documented cases in which children's neural-tube defects were linked to their mothers' visits to tanning studios during early pregnancy. Moreover, she found that folate is crucial to sperm development -- so much so that a folate inhibitor was developed as a male contraceptive. ("It never got anywhere," Jablonski says. "It was so effective that it knocked out all folate in the body.") She now had some intriguing evidence that folate might be the driving force behind the evolution of darker skin. But why do some people have light skin?

 

 

As far back as the 1960s, the biochemist W. Farnsworth Loomis had suggested that skin color is determined by the body's need for vitamin D. The vitamin helps the body absorb calcium and deposit it in bones, an essential function, particularly in fast-growing embryos. (The need for vitamin D during pregnancy may explain why women around the globe tend to have lighter skin than men.) Unlike folate, vitamin D depends on ultraviolet light for its production in the body. Loomis believed that people who live in the north, where daylight is weakest, evolved fair skin to help absorb more ultraviolet light and that people in the tropics evolved dark skin to block the light, keeping the body from overdosing on vitamin D, which can be toxic at high concentrations.

 

By the time Jablonski did her research, Loomis's hypothesis had been partially disproved. "You can never overdose on natural amounts of vitamin D," Jablonski says. "There are only rare cases where people take too many cod-liver supplements." But Loomis's insight about fair skin held up, and it made a perfect complement for Jablonski's insight about folate and dark skin. The next step was to find some hard data correlating skin color to light levels.

 

Until the 1980s, researchers could only estimate how much ultraviolet radiation reaches Earth's surface. But in 1978, NASA launched the Total Ozone Mapping Spectrometer. Three years ago, Jablonski and Chaplin took the spectrometer's global ultraviolet measurements and compared them with published data on skin color in indigenous populations from more than 50 countries. To their delight, there was an unmistakable correlation: The weaker the ultraviolet light, the fairer the skin. Jablonski went on to show that people living above 50 degrees latitude have the highest risk of vitamin D deficiency. "This was one of the last barriers in the history of human settlement," Jablonski says. "Only after humans learned fishing, and therefore had access to food rich in vitamin D, could they settle these regions."

[Firedragon52]

Great post, coquina. Thanks.

[ydoaPs]

We all know why humans initially had darker skin. (Protection from the sun.)

 

 

could you provide any shred of evidence for your claim?

[Firedragon52]

could you provide any shred of evidence for your claim?

 

Here's a site that coquina presented on this very thread

http://www.pbs.org/wgbh/evolution/library/07/3/text_pop/l_073_04.html