Issues

What are some issues of skin color variation? Why do people from different countries have different colored skin? Variations in human skin color are adaptive traits that correlate closely with geography and the sun's ultraviolet (UV) radiation. There are so many issues about human skin color variation. The actual skin color of different humans is affected by many substances, although the single most important substance is the pigment melanin. Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin color of darker skinned humans. The skin color of people with light skin is determined mainly by the bluish white connective tissue under the dermis and by the hemoglobin circulating in the veins of the dermis. Another issues are:

• The loss of body hair created another problem: it exposed the skin to strong UV radiation, which resulted in natural selection for darker skin to absorb the radiation and protect the body.
  
• At low levels of UV light, it may take a dark skinned person two hours to produce the same amount of vitamin D as someone with light skin produces in 15 minutes. Vitamin D deficiency, in turn, may cause health problems, such as osteoporosis and rickets.
  
• UV rays can cause skin cancer, because skin cancer usually affects people after they have had children, it likely had little effect on the evolution of skin color because evolution favors changes that improve reproductive success.
• Skin color does affect body temperature. Those living closer to the equator have more melanin. Melanin makes the skin darker, protects the skin from UV damage, and it also increases sensitivity to heat.
• According to a recent survey, there is a growing epidemic of vitamin D deficiency in the U.S. The problem tends to be worse in the winter, at higher latitudes, and in African Americans.
•  According to the survey, less than a quarter of all teens and adults have adequate blood levels of vitamin D, and fewer than five percent of African American teens and adults have enough of the vitamin.
• Genetic variants are affecting traits and show that mutations influencing light and dark skin have been around for a long time, since before the origin of modern humans.