Why Did Early Humans Begin to Develop Different Skin Tones Over the Past 100,000 Years? — Here’s What Researchers Found Out

The modern-day world is comprised of people with diverse skin colors, but it wasn’t always this way. Instead, early Homo sapiens and other hominins who existed before had a more uniform skin color. However, over the years, humans had to adapt to the changing environment and were forced to move to different places.

But, it’s not as simple as one population going to a place with more sunlight and becoming darker-skinned, or another group settling in colder environments with less UV radiation from the sun, and turning light-skinned. That is not how evolution works. It required a much complex interplay of different factors and adaptations to reach the point we are at today. So, let’s dive in at the very beginning.

The Starting Point — What Early Humans Probably Had

Scientists believed that our ancestors had pale skin before, and this was back when they still had thick fur, similar to the current-day chimpanzees. However, due to the changes in the climate and environment, they had to adapt to expanding open grasslands, savannas, and deserts, while forestry areas receded.

This created a series of transformations that helped them survive in these new circumstances around 2 million years ago. From bipedalism and walking upright, to the loss of fur, and increased sweating for thermoregulation. Soon, our ancestors had mostly become hairless, but without their thick fur to protect them from the harmful ultraviolet rays of the sun, they were at a disadvantage.

Over time and many generations, along with the evolution of other traits, they gradually adapted to have darker skin tones. This is most likely because individuals who have more natural melanin or pigments that darken the skin became more advantageous and had a higher chance of survival and reproduction. Then, thousands and thousands of years later, the majority of the population had adapted the trait and had a darker skin tone.

This was estimated to have happened long before Homo sapiens existed in Africa. But, soon, the modern human species arrived. Their ancestors also lived closer to the equator and in open areas, where the sun is directly above them. This condition was faced by most hominins in this continent, and thus they have retained the darker skin tone, which most likely evolved in the homo genus species long before them.

Read more: PubMed Central

The Pull of UV, Folate Protection, and Vitamin D

Population Genetics: Why do we have different skin colors?: Crash Course Biology #14

So, what made our species change skin tones when darker skin is very beneficial and advantageous in the environment in which we evolved in. Well, it involves another necessity for the human body, and that is the ability to make enough vitamin D. Under the scorching heat of the sun in Africa, this was probably not as big a problem, but in other environments, such as places with weaker sunshine, it is a significant part of survival.

Near the equator, early human populations had to deal with intense UV rays. The darker skin tone that they may have had inherited from earlier hominins acted as a natural sunscreen. Without it, too much ultraviolet radiation could damage the DNA and skin folate, which is a vitamin essential for cell growth and the making of DNA itself. These advantages made darker skin naturally favorable in these environments.

However, early humans also moved places, most likely in search of a new habitat where they could thrive and survive. In many cases, they were also forced out of their old environments because of climate change and lack of or exhaustion of resources. Some had to migrate to places with little to no sunshine. Then the trade-offs of a darker skin tone showed.

The pigmentation acted as a natural sunscreen, but too much of it could block the necessary UV rays for creating vitamin D in the body. Without sufficient vitamin D, the development of bones and the immune system suffers. In other words, the once advantageous darker skin tone was not, and the lighter skin tone in these environments became the more beneficial trait.

These phenomena created the observed pattern in the modern day, where there is a gradual shift in skin color based on latitude or the farther a place is from the equator.

Genes, Mutations, and Regional Paths

It is important to note that the changes in skin color were not from one single gene or mutation that happened in earlier human populations. Instead, scientists found dozens of genes that influence this trait. In fact, studies of ancient DNA showcased the presence of genes that could have impacted the lighter skin tones in the European population, and this only became more common recently in evolutionary terms, or within the last 100,000 years.

For most of that time, the lighter skin tone remained rare, and only about a few thousand years ago, when it became more widespread and more common throughout the whole continent. There are even some fossils and DNA studies that tell us that blue eyes may have come first, before the increase in the prevalence of lighter skin tone. Either way, the genes were already present; they were just not as established in the population.

Additionally, this was not the same alleles that made humans in Asia have lighter skin tones. It could have been a different gene than the ones that made the population in Europe have lighter skin. In other words, different groups arrived at the same results through various paths, signifying the importance of adaptation of skin color based on the environment in which a population lives.

Read more: PubMed: Adaptation of human skin color in various populations

What We Still Don’t Know

The Biology of Skin Color — HHMI BioInteractive Video

Despite all the DNA studies done on both ancient humans and the modern-day population, many questions still remain unanswered or unproven. For example, just how long til a group of humans adapts a lighter skin tone after migrating into a new environment where it is more advantageous or improves chances of survival? Some model suggests that it could have happened as early as 2,500 years or about 100 generations.

It is also unclear how different genes interact with each other over time and across different populations, as it was understood that no single allele caused the changes in skin tones, and that there are varying genes that influence it in different groups.

Additionally, how did culture come into play in this evolutionary history? The development of clothing, choice of shelter, and diet could all have played a role, or at least influenced these outcomes today. They may have changed the selective pressure of being exposed to the sun.

Author's Final Thoughts

The story of different skin tones dates back millions of years, back when our primate ancestors still had pale skin under their thick fur. But, because of the changing environment, where the forests receded and they were forced to live in open areas exposed to the sun. To adapt, several transformations happened, which include bipedalism, walking upright, increased sweating, and the loss of fur.

This resulted in individuals who have a darker skin tone being more naturally favorable and having increased chances of survival and passing on their genes. Soon, the darker skin became more established in the hominin populations.

However, another great change occurred, and gradually, different populations moved to different places where their inherited dark skin tones from earlier hominins became less advantageous. Lighter skin tones instead became the more beneficial trait in these new environments.

But since different human groups stayed in various habitats, dealing with their unique challenges and adapting to them, the modern-day populations became more diverse in terms of varying skin tones. This is a story that reminds us that the diversity in our skin colors is not just about differences, but it is about how our early human ancestors adapted to this ever-changing world.

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

References & Further Reading

Lucock, M. D. (2022). 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://pmc.ncbi.nlm.nih.gov/articles/PMC10083917/

Jablonski, N. G. (2022). 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/

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

Guermazi, D., & Saliba, E. (2022). The genetics and evolution of human pigmentation. Biology. https://www.mdpi.com/2079-7737/14/8/1026