Sunday, September 6, 2009

Human Skin

Natural Selection does not produce perfection. If your genes are good enough your offsprings will make it to the next generation. This is obvious in the populations around us. Individuals may have genes for genetic diseases, or they may not have genes to survive adverse conditions. No population or organism is perfectly adapted.

Dr. Nina G. Jablonski, who heads the anthropology department at Pennsylvania State University said:
"There was a tremendous takeoff in human evolution about two million years ago when primates who could no longer be called apes appeared in the savannahs of East Africa. These early humans ran long distances in open areas. In order to survive in the equatorial sun, they needed to cool their brains. Early humans evolved an increased number of sweat glands for that purpose, which in turn permitted their brain size to expand. As soon as we developed larger brains, our planning capacity increased, and this allowed people to disperse out of Africa. There’s fossil evidence of humans appearing in Central Asia around this time.."
"Skin color is what regulates our body’s reaction to the sun and its rays. Dark skin evolved to protect the body from excessive sun rays. Light skin evolved when people migrated away from the Equator and needed to make vitamin D in their skin. To do that, they had to lose pigment. Repeatedly over history, many people moved dark to light and light to dark. That shows that color is not a permanent trait."
This illustrates neither darker nor lighter skin coloured populations are perfectly adapted to climate variations in different parts of the world. In winter an African American living in Northern USA must expose her skin to sun rays for much longer periods in order to have adequate vitamin D absorption. Similarly lighter skin coloured individuals who live in sunny climates are less protected against harmful UV radiation due to their skin's increased light absorption capability.


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