The story of our skin – where does skin colour come from? On the sun, melanin, and evolution
Skin colour is the result of a brilliant survival strategy, encoded in our bodies over thousands of years. Skin pigmentation is no accident – it is nature’s precise response to the amount of light in our environment.
In regions where UV radiation was intense, darker skin protected DNA. In places with less sunlight, lighter skin facilitated the synthesis of vitamin D, essential for bone health and immunity. It’s an extraordinary example of how our bodies have found a balance between protection and benefiting from sunlight.
Why does one person tan within minutes, while another can spend more time in the sun without any visible change?
Where did such a vast palette of skin tones come from – from porcelain white to deep black?
The answer takes us through evolution, genes, and… sunlight. As Angela Koine Flynn says in her TED-Ed animation:
“Whatever the colour, our skin tells an epic tale of human intrepidness and adaptability.”
Melanin – more than just pigment
Melanin is a biological guardian, not merely “skin colour.” It protects cellular DNA from harmful UV radiation, helps maintain the skin’s thermal balance, and influences the immune system.
It exists in two main forms:
- Eumelanin – gives skin and hair shades of brown and black, absorbs over 99.9% of UV radiation, and neutralises free radicals.
- Pheomelanin – responsible for reddish tones and freckles, absorbs less UV, and in excess can contribute to the formation of free radicals.
Melanin is produced by melanocytes – cells located in the deepest layer of the epidermis. The pigment is enclosed in microscopic “capsules” called melanosomes.
Dark and light skin differ mainly in:
- Number of melanosomes – dark skin has more of them.
- Size – in dark skin, they are larger and more pigmented.
- Distribution – in dark skin, they are evenly dispersed; in light skin, they are clustered.
A cross-section of the epidermis shows the differences in the structure and arrangement of skin pigmentation components in people of different origins. The most important difference concerns melanosomes – microscopic “capsules” of melanin produced by melanocytes:
- African skin – melanosomes are large, numerous, and evenly dispersed within keratinocytes throughout the entire thickness of the epidermis. This provides strong and uniform protection against UV radiation.
- Asian skin – melanosomes are medium-sized and fewer in number, distributed less evenly.
- European skin – melanosomes are smaller, fewer, and often grouped.
The pink oval shapes inside the cells are cell nuclei, which control processes within the cells. The large cell with dendritic extensions at the base of the epidermis is the melanocyte – a specialised cell that produces melanin and transfers it to neighbouring keratinocytes.
The diagram illustrates a gradual variation in the size and number of melanosomes in dark, intermediate, and light skin; moreover, in dark skin, melanosomes are more evenly dispersed.
The sun as an evolutionary force – A story of migration
Skin colour is a compromise between protection against UV radiation and the ability to synthesise vitamin D. At the equator, intense UV radiation damages DNA. Dark skin with high levels of eumelanin protects against this effect. In temperate and polar regions, UV radiation is weaker, but it is still necessary for vitamin D production. Light skin allows UVB rays to penetrate more easily, thereby supporting the synthesis of vitamin D.
Exceptions: The Inuit and other Arctic people have retained darker skin due to a diet rich in vitamin D from fish and marine fat.
Migrations over the past 50,000 years led to the emergence of different skin tones independently in various populations – an example of convergent evolution. In other words, nature “invented” the same solution independently in several parts of the world.
Light and the skin’s response
When UV radiation reaches our skin, it triggers a chain of protective reactions. Special light-sensitive receptors, called rhodopsin, detect the light and stimulate melanocytes to produce melanin. In people with fair skin, an increase in melanin results in a visible darkening of the skin – a tan. In people with darker skin, who have a higher threshold for melanin production and a greater amount of eumelanin, the protective effect is constant and less dependent on short-term sun exposure.
This ability of the skin to respond to UV is an evolutionary compromise – it protects us from DNA damage while also allowing vitamin D production when sunlight is scarce.
Skin colour – Nature’s signature on our story
Skin colour is the result of thousands of years of interaction with sunlight, evolution, and adaptation.
Each shade is a trace of our ancestors’ journeys, a testament to their ability to survive in different environments. When we look at the diversity of pigmentation, we don’t see division – we see a map of our shared history written on our skin.
This is just the beginning of the story…
Skin colour is only the tip of the iceberg. In the upcoming parts of the series “The story of our skin”, we’ll explore the genes behind pigmentation, the role of vitamin D and B9, how migration shapes skin health, and what NASA satellites reveal about UV radiation across the globe. If you’re curious about how biology, climate, and history have shaped human skin – stay with us. More articles from this series are coming soon.
Want to know how to determine your “skin type” and choose the right sun protection for it? Check out our guide to skin phototypes.
We also recommend some fascinating materials on YouTube if this topic has sparked your curiosity:
Sources – Article inspired by the following materials:
– How We Get Our Skin Colour – Narrated by anthropologist Nina Jablonski | HHMI BioInteractive Video, 2015
– The science of skin colour by Angela Koine Flynn, TED-Ed Animation, 2016
– What Controls Variation in Human Skin Colour? – Gregory S. Barsh, Published at PLOS Biology: October 13, 2003
– Skin colour is an illusion by Nina Jablonski, TED Talk 2009