Anatomy And Physiology

Anatomy Physiology



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Genetic studies have demonstrated that there is a remarkable similarity between any two human beings. These findings have dismantled any argument that seeks to project race as a major division among men. In fact it appears that there is so little genetic difference among races that the very concept of race is remarkably superficial.

So how did these various skin tones emerge? There are two major theories regarding the emergence of Homo sapiens. One theory called the Multi-Regional Evolution theory suggests that various groups of ancient people existed in diverse regions millions of years ago. Each evolved independent of each other and adapted to their environment. In this situation, there would have been major genetic differences among human populations and all populations would be equally diverse. A competing theory is the Out of Africa Replacement theory. This latter model, states that ancient man was present only in Africa until fairly recently by evolutionary standards (about 140,000 years ago), and then through migration encountered different climates that he adapted to.

It is now generally accepted that the Out of Africa theory is correct and that man evolved only in Africa until recently. Only this theory could explain why there is so little genetic diversity among races today and why the genetic diversity among Africans is more than among any other group.

The Out of Africa theory also explains the differences in skin tones. The original people from Africa would have been adapted to the warmer climate and greater level of sun exposure of this region. These climactic conditions resulted in the elevated production of melanin in their skins. This compound helps to protect the skin from the UV radiation in their natural environment. As ancient populations moved to colder and less sunny climates, they no longer required to same level of protection. This would lead to a selective pressure to decrease the amount of melanin in the skin. Over time these populations therefore became lighter skinned due to the reduced melanin content. This is a classic example of natural selection driven by migration that led to the adaptation of Homo sapiens to their new and diverse environments. Interestingly, it is this lack of melanin that is considered to be one of the reasons why these lighter-skinned populations are more prone to skin cancers when exposed to high levels of UV radiation to which they are not well adapted.

Yours in Health

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