Imagine a world where everyone had brown skin. Tens of thousands of years ago, that was the case, say scientists at Pennsylvania State University. So, how did white people get here? The answer lies in that tricky component of evolution known as a genetic mutation.

Out of Africa

Scientists have long known that Africa is the cradle of human civilization​. There, our ancestors shed most of their body hair around 2 million years ago, and their dark skin protected them from skin cancer and other harmful effects of UV radiation. When humans began leaving Africa 20,000 to 50,000 years ago, a skin-whitening mutation appeared randomly in a sole individual, according to a 2005 Penn State study.﻿﻿ That mutation proved advantageous as humans moved into Europe. Why? Because it allowed the migrants increased access to vitamin D, which is crucial to absorbing calcium and keeping bones strong.

"Sun intensity is great enough in equatorial regions that the vitamin can still be made in dark-skinned people despite the ultraviolet shielding effects of melanin," explains Rick Weiss of The Washington Post, which reported on the findings. But in the north, where sunlight is less intense and more clothing must be worn to combat the cold, melanin's ultraviolet shielding could have been a liability.

Just a Color

This makes sense, but did scientists identify a bonafide race gene as well? Hardly. As the Post notes, the scientific community maintains that "race is a vaguely defined biological, social, and political concept...and skin color is only part of what race is—and is not."

Researchers still say that race is more of a social construct than a scientific one because people of purportedly the same race can have as many differences in their DNA as people of separate so-called races do. It's also difficult for scientists to determine where one race ends and another begins, considering that people of supposedly different races may have overlapping features in terms of hair color and texture, skin color, facial features, and other characteristics.

Members of Australia's aboriginal population, for example, sometimes have dark skin and blond hair of various textures. They share traits with people of African and European ancestry alike, and they are far from the only group not to fit squarely into any one racial category. In fact, scientists posit that all people are roughly 99.5% genetically identical.

The Penn State researchers' findings on the skin-whitening gene﻿﻿ show that skin color accounts for a minuscule biological difference between humans.

"The newly found mutation involves a change of just one letter of DNA code out of the 3.1 billion letters in the human genome—the complete instructions for making a human being," the Post reports.

Skin Deep

When the research was first published, scientists and sociologists feared that the identification of this skin-whitening mutation would lead people to argue that whites, Blacks, and others are somehow inherently different. Keith Cheng, the scientist who led the team of Penn State researchers, wants the public to know that's not so. He told the Post, "I think human beings are extremely insecure and look to visual cues of sameness to feel better, and people will do bad things to people who look different."

His statement captures what racial prejudice is in a nutshell. Truth be told, people may look different, but there's virtually no difference in our genetic makeup. Skin color really is just skin deep.

Not So Black and White

Scientists at Penn State continue to explore the genetics of skin color. In a 2017 study published in the journal Science,﻿﻿ researchers report their findings of even greater variants in skin color genes among native Africans.

The same appears to be true of Europeans, given that, in 2018, researchers used DNA to reconstruct the face of the first British person, an individual known as the "Cheddar man" who lived 10,000 years ago. The scientists who took part in the reconstruction of the ancient man's face say that he most likely had blue eyes and dark brown skin. While they do not know for sure what he looked like, their findings dispute the idea that Europeans have always had light skin.

Such diversity in skin color genes, says evolutionary geneticist Sarah Tishkoff, the lead author of the 2017 study, likely means that we can't even speak of an African race, much less a white one. As far as people are concerned, the human race is the only one that matters.