How genetics is revealing skin colour biology is more than skin-deep Premium

Skin's diverse history, genetics, and social implications explored, shedding light on human evolution and societal complexities.

Skin, with its wide spectrum of textures, hues, and histories, has long captivated the imagination of poets and storytellers. It has served as a canvas for the expression of beauty, identity, and cultural symbols. The diversity of skin colour across human populations is a product of human genetics, the migration of peoples, and the complex interplay between genes and the environment.

Together with its colour, skin opens a window into the underlying human pathophysiology, and not just because it’s the largest organ, and has as a result been the subject of many scientific and medical investigations as well. The natural colour of human skin and changes therein help clinicians diagnose a number of medical conditions. For example, genetic defects can result in the absence of pigmentation by birth, such as albinism; partial or complete depigmentation can also result in disorders like vitiligo. A number of drugs, including antimalarials and chemotherapy agents, also cause skin pigmentation.

But for all of skin’s significance and wonder, its colour has also been the basis of social hierarchies, racism, and other forms of discrimination. Recognising the biological basis of skin and celebrating the diversity of skin colour could instead foster a deeper appreciation of human differences and promote inclusivity.

The pigment melanin determines the colour of skin. It is produced by cells called melanocytes. A number of genes and factors influence the type and size of melanin particles as well as its production, transport, and distribution.

Scientists widely believe exposure to ultraviolet light from the Sun has been the dominant driver of skin colour throughout history. Across geographies, colours have also displayed a close connection to the latitude, which in turn is correlated with ultraviolet exposure. There is also consensus that lighter skin colour across higher latitudes is the result of humans adapting to produce vitamin D — again, a process induced by ultraviolet light. Skin pigmentation also protects nutrients like folate from being broken down by ultraviolet radiation.

This said, systematic approaches to understand and document skin colour have been only of recent interest. In 1735, the Swedish biologist Carl Linnaeus classified humans into four ‘varieties’ based on skin colour. The Austrian anthropologist and explorer Felix von Luschan designed a scale with which to compare skin colour in the 19th century. The scale has 36 colours and is used to this day.

Dark-skinned humans evolved from apes around 1.2 million years ago by shedding body hair and adapting to ultraviolet radiation. Skin colour is also one of the more striking phenotypes (attributes produced by genes’ interactions with the environment) in humans, being closely related to their migration and adaptation as they moved out of Africa around 100,000 years ago.