What are the biological factors that influence skin tone?

The skin color of your ancestors plays a key role in determining your skin tone, which is primarily shaped by the biological factor of genetics. However, the geographical location of your ancestors explains why there is a diversity in human skin tones.

Consider the distant past. People living near the equator were exposed to stronger UV light, while those residing closer to the poles encountered much less UV exposure. As a result, their skin adapted by producing melanin, a pigment that protects the skin from UV radiation. The more melanin your skin produces, the darker your skin tone. This is a biological factor. But what about individuals whose skin tone doesn't match the typical pattern of where their ancestors lived? This is where genetics comes into play.

There are other genes and biological factors that contribute to skin tone. Our genetic makeup manifests as a phenotype, a visible characteristic such as skin color. These phenotypes can be influenced by multiple genes, known as polygenic traits, which explain the vast range of skin tones seen around the world today.

Certain genes have been linked to skin tone, including ASIP, MATP, TYR, and OCA2 [source: Shriver]. However, none are as influential as the gene SLC24A5, which was only identified in recent years. Although previously overlooked, research from Penn State University has shown that SLC24A5 plays a significant role in skin tone, contributing to up to 38 percent of an individual's skin color [source: BBC News].

The majority of people possess one version of the SLC24A5 gene. A variant found in Europeans carries a mutation that results in lighter skin. Studies have revealed that individuals with ancestors from both Europe and West Africa – where the more common form of the gene originates – show lighter skin depending on whether they inherited the original or the European mutation of SLC24A5 [source: BBC News].