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Climate and Disease
Other important factors of environmental factors include climate and disease. Climate has effects on determining what kinds of human variation is more adaptable to survive without much restrictions and hardships. For example, people, who live in the climate where there is a lot of exposure to sunlight, has a darker color of skin tone. With evolution favors protection of folate (folic acid) from UV radiation, they have darker skin tone with more melanin to make sure child development is smooth and success. On the other hand, people who lived further away from the equator has lighter skin tone. They have lighter skin tone because they need more exposure and absorbance of sunlight to make sure the body produce enough vitamin D for survival.

Blackfoot disease is a disease caused by environmental pollution and causes people to have black, charcoal-like skin in the lower limbs. This is caused by arsenic pollution in water and food source. This is an example of how disease can affect human variation. Another disease that can affect human variation is syphilis, a sexual transmitted disease. Syphilis does not really affect human variation until the middle stage of the disease. It then starts to grow rashes all over the body, affecting people's human variation.

See Also:

 * High-altitude adaptation
 * Effects of high altitude on humans
 * List of cutaneous conditions