Why Did Early Humans Develop Darker Skin Around 1.2 Million Years Ago? — Here’s What Scientists Found Out

Humans today all have different skin tones, ranging from very light to very dark; however, this was not always the case. Scientists believe that just like our closest living relative, chimpanzees, early humans may have had light skin that was covered and protected by their thick fur.

This fur kept them safe from the sun, and it made them warm in colder climates because it traps heat. However, the world changed, and the environment shifted. There’s something that happened millions of years ago for us to lose our fur, and that’s when we probably developed darker skin. But why exactly did early humans develop darker skin? Let’s dive deeper into one of the most significant adaptations in human history.

From Fur-Covered Skin to Bare Skin

Over 2 million years ago, early humans still had their thick fur. They also mostly live in shaded forests, surrounded by tall trees. Their thick hair helped block the sunlight that passed through the shades, it kept biting bugs away, and regulated their body temperature for the specific climate during that time. Under that fur was believed to be a pale skin tone because the sun’s UV rays couldn’t reach it, just like with chimpanzees today whom modern humans share up to 99% DNA.

However, climate change and the habitats they once knew shifted with it around 2 million to 1.5 million years ago. Some forests receded, and open areas like savannas and grasslands expanded. Several species were forced to adapt to this new environment. Earlier humans developed bipedalism and walking upright. Then they evolve to be able to run long distances to hunt for food or look for resources. Thick fur would have been a problem for this environment because it traps heat efficiently, which could have made humans overheat under the sun.

To stay cool, earlier humans started to sweat more, and evolution naturally favored individuals who could release heat better, which in this case means less fur for the sweat to evaporate as it comes into contact with air. Over time, our ancestors became mostly hairless, and their skin became exposed to the harmful sunlight.

Before the continuation of this process, it is best to keep in mind that all these mentioned adaptations did not happen in isolation. It is mostly a series of gradual changes all happening simultaneously at various timelines. In short, they are interconnected evolutionary adaptations estimated to have happened around those years.

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Once the thick fur was mostly gone, they believed pale skin underneath was now in danger of being unprotected. In the scorching heat of the sun in Africa’s open grasslands and savannas, the bare skin would have been bombarded by the harmful ultraviolet rays.

These could have negative effects on earlier humans, such as severe damage to the DNA, skin diseases, and destruction of skin folate, which is a vitamin essential for making DNA and healthy cells. So, early humans with naturally more melanin, or the pigment that darkens the skin, were more advantageous.

Since melanin and darker skin tone act like a sunscreen, they prevent the harmful effects of prolonged exposure to the sun. It absorbs and then scatters the UV radiation before it can reach the deeper layer of the skin and begin harming the inner tissues.

Life back then involved persistence hunting, where early humans stalked, tracked, and chased their prey until they were exhausted and too weak to fight. It was one of the main survival strategies, along with gathering and scavenging resources under the scorching heat of the sun.

People with more melanin and naturally darker skin tone were able to stay longer in this condition. They probably were able to gather more resources as they could stay outside longer, and their chances of survival increased, or at least were higher than those who had lighter skin. Over many generations, this became the dominant skin tone of early humans as it was naturally selected and favored for survival.

Genetic research also helped in confirming these hypotheses and that these transformations happened at around these timelines. They have found genes like MC1R, MFSD12, DDB1, and others more which are all linked to the pigmentation of the skin. The African population also showed that they have genes that increase melanin production, which dates back hundreds of thousands of years, to even over a million years ago.

Homo sapiens, or the modern human species, was believed to have only existed for 300,000 years. This meant that the darker skin transformations likely preceded our arrival, and that it may have been the default and dominant skin already for most other hominins that came before us.

Read more: PNAS: Human skin pigmentation as an adaptation to UV radiation

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The Evolution and Meanings of Human Skin Color | Nina Jablonski

The evolution of darker skin, as it was described, was not in isolation. It was part of a larger change happening in the homo genus species triggered by the shifts in our environment, and the necessities to survive and reproduce. One of these changes was our thermoregulatory systems. Since our ancestors transitioned to open areas where they are exposed to the sun, a better cooling system has been needed or has become advantageous.

So part of this system may have involved several evolutionary adaptations, such as bipedalism, standing upright, loss of fur, and then the darkening of skin tones. It is a complex interplay of transformations that made early humans adapt to a hot environment and gain more endurance. It is a reminder that our ancestors’ dark skin, and even today, is not just about looks that was passed down, it was an ancient record of how early humans survived and adapted to the changing world.

Author's Final Thoughts

Humans may have had different skin colors today, but a long time ago, most had darker skin, and if you went back even further, it would have been pale skin underneath a thick fur. So, in other words, the color of our skin contains a story not of difference between us, but that of survival and adaptation. It connects us to the same ancestors who walked, endured, and changed under the same hot sun millions of years ago.

Read next: How Did Australopithecus Survive in Africa for Nearly 2 Million Years Before Going Extinct? — Here’s What Researchers Discovered

References & Further Reading

Jablonski, N. G. (2021). The evolution of human skin pigmentation involved the interactions of genetic, environmental, and cultural variables. Pigment Cell & Melanoma Research. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8359960/

Jablonski, N. G., & Chaplin, G. (2010). Human Skin Pigmentation as an Adaptation to UV Radiation. In In the Light of Evolution: Volume IV: The Human Condition. National Academies Press. https://www.ncbi.nlm.nih.gov/books/NBK210015/

Sturm, R. A., & Duffy, D. L. (2012). Human pigmentation genes under environmental selection. Genome Biology. https://genomebiology.biomedcentral.com/articles/10.1186/gb-2012-13-9-248

Lucock, M. D. (2023). The evolution of human skin pigmentation: A changing medley of vitamins, genetic variability, and UV radiation during human expansion. American Journal of Biological Anthropology. https://pubmed.ncbi.nlm.nih.gov/36790744/

Ju, D., & Mathieson, I. (2021). The evolution of skin pigmentation–associated variation in West Eurasia. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.2009227118