The sun burns 92 million miles away and emits light of multiple wavelengths (aka solar radiation), reaching our eyes and our skin in a matter of minutes. This light is important for synthesis of pre-vitamin D, helping us integrate calcium into our bones and other health benefits. However, this light can cause harm to skin by inducing mutations in our DNA, leading to cancer. It also reduces folate, which is essential for pregnant mothers to have healthy babies.
How has evolution assisted in protecting us from these harmful rays? The answer is melanin, created by melanocytes (pigment producing cells) at the base of our epidermis. Melanin protects our skin cells DNA by covering and absorbing or reflecting varying wavelengths of light. But, not all melanin is created equal, hence skin color variation.
Two types of pigment exist: pheomelanin, the pigment responsible for white skin and eumelanin, the pigment that causes darker skin. Melanin is important for other species as well; for protection, camouflage, and regulating body temperature. As we evolved from our nearest proposed biological relatives, we lost hair and increased melanin production in our skin to enhance our chances of survival at varying intensities of light exposure.
By global climate and anthropological analysis, science shows there is a correlation between skin color and UV intensity in a geographical area. Near the equator and Africa, which receive the most direct sunlight, people have darker skin. As ancient dark skinned people lived outside, it was easy to get enough pre-vitamin D from the sun, while benefitting from melanin protection. As our ancient ancestors migrated north to areas of less direct sunlight (today’s Northern Europe and Scandinavian countries), it became more difficult to create pre-vitamin D so eumelanin was no longer needed to protect the skin’s DNA from the decreased amount of harmful light. Natural selection created a switch from eumelanin to pheomelanin and the emergence of light skinned people.
There are two main problems we face in modern times regarding skin color: people move or travel to climates for which their skin is not suited and racism toward skin color type which leads to social injustice.
Health-wise, fair skinned people in sunny climates should always protect their skin from burning or excessive tanning. This can lead to photo damage, pre-cancers and skin cancers. This is why there are many skin cancers in light skinned individuals in the US southern states, Australia, and those living near the equator. Darker skinned people should consider a vitamin D supplements if they live in darker climates or are indoors the majority of the day.
With variation in skin color, we have unjust racism, which proposes that one skin color is better or worse than another, which is completely false. It is important to understand that we are all one human race, all one species and all related by evolution.
We must embrace and appreciate the variations of skin color and understand the health risks related to our modern way of living in different parts of the world.
Please see this excellent video about the evolution of skin color. The Biology of Skin Color, HHMI.