How does skin color vary among individuals?

Skin color primarily varies among individuals due to the type and amount of melanin produced by melanocytes in the skin. Melanin is a pigment that comes in different forms, mainly eumelanin (which can be brown or black) and pheomelanin (which is yellow or red). The concentration and type of melanin determine a person's skin tone, with higher levels of eumelanin resulting in darker skin, while lower levels can lead to lighter skin tones. Additionally, genetic factors play a significant role in melanin production, which explains the wide range of skin colors observed among different populations.

While diet and environmental factors can influence skin appearance to some extent, such as through tanning or certain dietary pigments, the fundamental determinant of skin color is the melanin content. Keratin plays a crucial role in the structural integrity of the skin but does not affect pigmentation. The thickness of the epidermis can vary due to different biological factors, but it is not a primary factor in determining an individual's skin color. Therefore, the correct choice accurately reflects the biological basis for variations in skin color among individuals.