The Biology of Skin Color

Full Answer Section

• Skin cancer: While skin cancer is a significant health concern, it typically develops later in life, after reproductive age. Therefore, natural selection would have prioritized the protection of folate, which is essential for reproductive success.

4. Selective Pressure Favoring Light Skin

In regions far from the equator, where UV radiation is less intense, light skin has been favored by natural selection. This is because lighter skin allows for greater vitamin D synthesis. Vitamin D is essential for calcium absorption and bone health. In areas with limited sunlight, lighter skin can help individuals obtain sufficient vitamin D.

5. Populations at Risk for Rickets

Populations living in regions with low sunlight exposure, such as those in northern latitudes or individuals with limited sun exposure due to cultural practices, are at higher risk for rickets. This is because they may not produce enough vitamin D, leading to weakened bones and skeletal deformities.

Sample Answer

1. Function of Melanin in Humans and Other Species

In Humans:

• Protection from UV Radiation: Melanin, particularly eumelanin, is a pigment that absorbs UV radiation, shielding the skin from its harmful effects, such as skin cancer.
• Temperature Regulation: Melanin can help regulate body temperature by absorbing heat from sunlight.

In Other Species:

• Camouflage: Many animals, such as chameleons and octopuses, use melanin to change their skin color and blend into their surroundings.
• Sexual Selection: In some species, melanin pigmentation is linked to mate choice and reproductive success.

2. Lack of Diversity in MC1R Allele Among African Populations

The film suggests that the lack of diversity in the MC1R allele among African populations may be due to the strong selective pressure for dark skin in regions with high UV radiation. Dark skin, controlled by the MC1R gene, provides optimal protection against UV damage. Over time, this selective pressure has led to the fixation of the dark skin allele in African populations.

3. Evolutionary Advantage of Dark Skin

Dark Skin and UV Radiation:

• Protection against folate degradation: UV radiation can degrade folate, an essential nutrient for cell growth and development. Dark skin provides better protection against folate degradation, reducing the risk of birth defects and other health problems.