Тематический сборник текстов для чтения (английский язык). Соснина Е.П - 24 стр.

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under equal sun conditions. Furthermore, dark skin prevents UV-A radiation from

destroying the essential B vitamin folate. Folate is needed for the synthesis of DNA in

dividing cells and too low levels of folate in pregnant women are associated with birth

defects. The advantage of light skin is that it lets more sunlight through, which leads to

increased production of vitamin D

, necessary for calcium absorption and bone growth. The

lighter skin of women results either from sexual preference or from the higher calcium

needs of women during pregnancy and lactation (also possibly from both).

The evolution of the different skin colors is thought to have occurred as follows: the

haired ancestor of humans, like modern great apes, had light skin under their hair. Once the

hair was lost, they evolved dark s kin, needed to prevent low folate levels s ince they lived in

sun-rich Africa. When humans migrated to sun-poorer regions in the north, low vitamin D

levels became a problem and light skin color evolved.

The color of human skin varies from dark dark chocolate to white white chocolate. In

attempting to discover the mechanisms that have generated such a wide variation in human

skin color, the researchers Nina Jablonski and George Chaplin (2000) discovered that there

is a high correlation between the coloration of the human skin of indigenous peoples and the

average annual ultraviolet (UV) radiation available for skin exposure where the indigenous

peoples live. In considering the color of human skin in the long span of human evolution,

Jablonski and Chaplin note that there is no empirical evidence to suggest that the human

ancestors six million years ago had a skin color different from the skin color of today's

chimpanzees--namely white under black hair. But as humans evolved to lose their body hair

a parallel evolution permitted human populations to turn their base skin color dark or white

over a period of less than a thousand years to adjust to the competing nature demands.