About Your Skin

“I see it as my autobiography. My skin has seen everything that I have, all of the weather, the sorrow, the happiness, the toil. I love the changes that I see in my skin, and I see it as part of my human story.”

“The key insight behind our research is that protective melanin pigmentation evolved primarily not to protect us from skin cancer but to preserve our folate so that we could continue to reproduce.”

“Given all of the advantages of melanin, why doesn’t everyone have dark skin today? For most of human history, we did. What we see today is the product of evolutionary events resulting from the dispersal of a few human populations out of Africa around 60,000 to 70,000 years ago. Our species, Homo sapiens, originated around 200,000 years ago and underwent tremendous diversification—culturally, technologically, linguistically, artistically—for 130,000 years before a few small populations left Africa to populate the rest of the world. These early ancestors of modern Eurasians dispersed into parts of the world that had more seasonal sunshine and much lower UV levels. It’s in these populations that we begin to see real changes in the genetic makeup of pigmentation. As people move into areas with much lower and more seasonal UV, they run into problems if they have too much natural sunscreen. Some UV is essential for making vitamin D in the skin.”

“If we’re going to talk about skin color, we also have to talk about how we separate people into racial categories. How should we understand race, scientifically? I think it’s important to understand this from a few different perspectives. When we look at genetic diversity, we can see there are no clean breaks between human populations. Individuals have different groups of genes, so we see rough-and-ready kinds of biological groupings, but these blobs of genetic variation overlap and grade into one another. There are no clear demarcation lines. This is one of the reasons, the primary reason, why geneticists have said there are no human races from a biological perspective.”

“So race is strictly a social construction? Yes, but that doesn’t make it any less real. When people identify as belonging to a certain group, the biological or philosophical status of the race doesn’t really matter. So race is a very durable construct and people have strong racial identities that are often tied up with physical appearance, but also include a lot of cultural aspects.”

“But it would seem there are some physical differences between races. For instance, people of West African origin dominate the world-class sprinting competitions. This raises a very interesting question: Would you put West Africans in a separate race? Most people wouldn’t because their biological characteristics have so much overlap with people from East Africa, where people have tremendous abilities in long-distance running but not in sprinting. You can see concentrations of people with certain attributes, but these attributes overlap with nearby and even distant populations. So drawing a definite line of demarcation becomes impossible. And if you’re looking at a characteristic like sprinting ability, this requires biological ability in a person’s skeletal muscles. It also requires tremendous amounts of training, so there’s a huge cultural component. You can’t have just one or the other.”

“If our bodies evolved to develop certain differences, such as skin pigment, wouldn’t we also expect variations to evolve in our brains in response to local pressures? So wouldn’t the social behavior of different racial groups also be shaped by evolution? For over 2 million years, our brains got larger along with the technology we developed to manipulate the environment and our fellow human beings. Over time this process was based on cultural rather than biological innovations, with most of the biological specialization of the modern human brain established before 70,000 years ago, when humans started leaving Africa and dispersing into Eurasia. We can’t rule out the possibility of genetically based specializations of the brain over the last 70,000 years, but this has undoubtedly been very minor. All modern humans share tremendous abilities to observe and remember and respond with uncanny behavioral flexibility to all kinds of complex problems. The evolution of human skin, by contrast, has really only been affected by cultural evolution in the last 20,000 years, when we see sewn clothing and complex shelters. Before that, skin was the primary interface between our bodies and the physical environment. The tremendous variety of skin colors that we see today owes to local natural selection and also to genetic drift, which restricted the gene pools—and the variation of pigmentation genes—in many small, dispersing populations.”

“Steve Paulson is the executive producer of Wisconsin Public Radio’s nationally syndicated show “To the Best of Our Knowledge.” He’s the author of Atoms and Eden: Conversations on Religion and Science.”