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A Penn Genetics Professor Wants to Change How We Think About Race

For most of us, the association of skin color with race is automatic. Sarah Tishkoff’s research shows it’s nothing of the sort.


sarah tishkoff

Artist Angélica Dass rethinks the concept of race by showing the diversity of human skin colors in her global photographic mosaic. Image by Angélica Dass | Humanae Work in Progress (Courtesy of the artist)

Three decades ago, a white couple I know was awaiting the birth of a baby they were adopting. Not long after the delivery, the pediatrician called. “This may be a child of color,” he informed them, presumably in case that news would affect their decision to take the baby home.

At the time, when I heard this story, I was flummoxed. May be a child of color? Come on. Either it was or it wasn’t. Surely you could tell just by looking. Or with a blood test. Or some kind of test. Something as fundamental as race — something that has caused so much trouble and angst in this country, in this world — couldn’t just be a matter of guesswork, could it?

At the time, actually, it could.

Of course, that was 30 years ago, and the interim has seen an explosion of scientific discoveries regarding our genetic makeup. The human genome has been sequenced. Researchers have teased apart the hereditary bases of everything from cancer risk to weight to auburn hair. A host of enterprises like 23andMe, AncestryDNA and MyHeritage promise to pinpoint just where your ancestors came from. And what, exactly, have these scientific advances taught us about race? According to Penn geneticist Sarah Tishkoff, that when it comes down to our genes, there simply isn’t any such thing.

In her field, Tishkoff, 53, is a Really Big Deal — or, as the National Academy of Sciences puts it, “a leading global expert in human evolutionary genetics.” After reading Margaret Mead’s Coming of Age in Samoa while coming of age in Oregon, she earned a bachelor’s degree in anthropology and genetics at UC Berkeley and master’s and PhD degrees in genetics from Yale. In her 11 years at Penn, she’s won a slew of honors; this month, the American Society of Human Genetics will present her with its prestigious Curt Stern Award for “significant scientific contributions during the past decade.” Some of her work involves genetics and disease risk, but mostly she studies the history and evolution of African populations through their genes.

“If you ask people on the street what ‘race’ means, skin color is the number one thing they’ll say,” Tishkoff tells me in a phone interview; she’s just back from abroad and too busy for a face-to-face. Our skin color is tied to our genes, but the idea of “race” reflects history and culture rather than genetic differences. “Take the racial classifications in our census,” Tishkoff says. “When you check the box that says ‘Hispanic,’ what does that mean? Someone who’s Hispanic can have differing amounts of African, European, Native American, Latin American heritage. It’s not a genetically pure group. It’s very heterogeneous.”

Still, the dominant culture gets to choose who’ll be “other,” and in America, white people have done the deciding. Think of the famous “March of Progress” illustration from Time Life’s Life Nature Library series — the chart officially titled “The Road to Homo Sapiens.” It shows in a row, from left to right, 15 different primate species, from the “ancestor of the gibbon line” at the start to “modern man” at the finish. Along the way, the exemplars grow more upright, taller, handsomer, more recognizably us. That 1965 rendering accords with a general Western perception of how mankind got to where it is today. The further Homo sapiens moved from its cradle in East Africa, the more civilized it became, leaving behind its nakedness and hunter-gatherer ways to don hoop skirts and write great books and erect elaborate cathedrals before finally crossing the immense barrier of the Atlantic Ocean to achieve that apotheosis of civilization, the U.S. of A. Along the way, it also got … more pale.

Yet if you shave a chimpanzee, Tishkoff says — and personally, I feel that’s a mighty big if — you’ll find pale skin under the dark hair. The tree of evolution indicates that chimpanzees were the last great ape to evolve from the species that would later become humans­ — we share a common ancestor who lived between eight million and six million years ago. They’re our closest living relatives. Our DNA profiles are nearly 99 percent identical.

And they’re pale beneath all that hair.

Humans find it nearly impossible to resist viewing evolution as a continuing process of improvement. Why not, when, as Tishkoff says, we seem to be ensconced right at the top? But scientists who study evolution don’t view people as the “winners,” or adaptation as a matter of progress. Rather, it’s about organisms maximizing their reproductive potential in the environments where they find themselves.

The shared ancestors of Homo sapiens and the chimps lived in dense forests where they could swing from tree to tree. It was a change in their environment — movement away from that closed forest canopy — that propelled our human ancestors onto the ground. They became walkers instead of climbers, with longer legs and straighter backs and big toes that pointed forward instead of sideways. One could make the case that these hominins were losers, since they were the ones who had to leave the jungle, with its dense shade and plentiful food.

Our new environment precipitated further evolutionary changes. To thrive in the more open savannah, we developed an efficient total-body cooling system based on perspiration — one that required that we lose most of our bodily hair. And it was this loss that precipitated the evolution of darker skin.

Here’s a quick primer on what gives you hue. The chemical melanin comes in two forms that color skin, dark brown eumelanin and yellow-red pheomelanin, and is present in a wide array of organisms, from fungus to, well, us. If your pigment cells are filled with mostly eumelanin, you have dark skin. If they have mostly pheomelanin, you’re pale. Varying ratios of eumelanin to pheomelanin result in the wide spectrum of color in human skin.

When we’re exposed to intense sunlight, our pigment cells release eumelanin into our skin, creating what we call a “tan.” If you’re really pale, you don’t have much eumelanin available, and you just sunburn instead. Without eumelanin’s protection, the sun’s ultraviolet radiation (UVR) breaks down the chemical bonds in DNA, producing the dangerous molecules we call “free radicals” that disrupt normal chemical processes in cells and cause cancer.

So dark skin serves as a powerful sunscreen and protects against skin cancer. But since skin cancer typically doesn’t show up until we’re past reproductive age, preventing it doesn’t make much sense evolutionarily. Is there some function of melanin that matters while we’re still young and frisky?

Indeed there is. Meet folate.

A B vitamin present in citrus, leafy greens and whole grains, folate is a vital part of the chemical pathway through which the body replicates its DNA. In pregnant women, too little folate results in fetal neural-tube defects such as spina bifida. Folate also affects the ability to maintain healthy eggs, to have those eggs implant properly, and to develop a healthy placenta. (It helps men produce normal sperm, too.) UVR breaks down folate, but eumelanin protects against such damage by absorbing the UV. Darker skin proved so protective in terms of reproduction that in what’s known as a “selective sweep,” our equatorial ancestors who bore a gene variant for it quickly outnumbered those who didn’t.

This worked really well so long as we were hanging out near the equator. But eventually we struck out for more distant climes where the sunlight was less intense, particularly in winter and fall. We didn’t need as much protection from UVR, especially since it came at a cost: less vitamin D.

The so-called “Sunshine Vitamin” allows the body to absorb and use calcium and is required by just about every part of us, from our bones to our brains. UVR penetrating the skin starts the production of vitamin D. Near the equator, there’s enough sunlight that even darkly pigmented people can make enough vitamin D. But closer to the poles, there’s just not enough light, especially in fall and winter. Cue another selective sweep, this one in northern regions and in favor of a gene variant for lighter skin that let more UV through.

If you map the varying skin colors that result from this folate/vitamin D balancing act, you’ll see they circle the world in horizontal bands: darkest at the equator, paler as you move toward either pole. One exception are the Eskimo-Aleut, who live within the Arctic Circle. According to this schema, they should be pale. They’re not; they’re moderately pigmented and develop heavy tans from UVR reflected off water, ice and snow. Their diet of marine mammals, however, is rich enough in vitamin D to see them through the long, dark winters. There’s more than one way to adapt to fit the environment.

When Tishkoff started her work in genetics, there was plenty of DNA research material from Europeans and their descendants. From Africans, not so much. Earlier studies of a skin-color gene known as MC1R indicated that it was highly variable in Europeans but consistent within Africans. Tishkoff’s team gathered a range of African DNA and assessed the light reflectance of the volunteers’ underarm skin with a color meter. And it soon became clear that there’s far more genetic variation among the continent’s different populations than anyone imagined — more than anywhere else on Earth, in fact. “Genes for Skin Color Rebut Dated Notions of Race,” a 2017 New York Times headline on a story about their work proclaimed.

One gene with a variant considered “European” because of its association with light skin turns out to be present in East Africa; it just doesn’t lighten skin as much there as it does in, say, Norway, because of other variants. What’s more, Nilo-Saharan-speaking peoples — considered the world’s most darkly pigmented — have been evolving to be darker than they once were. It turns out that genetic variants for both dark and light skin have been present for at least 270,000 years, which is the widely accepted time period for the development of Homo sapiens. One of the oldest variants Tishkoff’s team found — estimated at a million years old — is for light skin. “Skin color is a complex trait,” Tishkoff says, “that’s the result of many different genes and the environment. There is no such thing as an ‘African race.’”

When early humans did strike out from Africa’s broad, diverse genetic sea, they took with them a handful of family members or fellow adventurers. When these isolated bands eventually settled, they bred within their group, so the genetic pools in places like Scandinavia and Indonesia and Mongolia are far less diverse than in Africa.

Okay; they didn’t just breed with each other. They also seem to have made new friends. Recent research has found traces of non-Homo sapiens DNA in lots of us. Specifically, Neanderthals, portrayed when their bones were first discovered in 1856 as clumsy sub-human oafs, may have been getting it on with your human ancestors hundreds of thousands of years ago; Europeans and Asians retain as much as four percent Neanderthal DNA. And a recent study by Tishkoff and her colleagues showed that Neanderthals also had gene variants for dark and light skin and may have come in pale and dark tones, too. Predictably, they’re seeing their reputation get a rehab now that we know they live on in us. The New York Times Magazine ran an article a few years back called “Neanderthals Were People, Too.”

The essential meaninglessness of our skin color is belied by its obviousness. We’re visual creatures, after all; we evolved to hunt with our eyes, not our ears or our sense of smell. And we’re tribal by nature. “It’s part of being human,” Tishkoff says. “We classify each other. Then we use those classifications to justify genocide and the Nazi Holocaust and slavery.”

A new book by Angela Saini, Superior: The Return of Race Science, details how misguided the concept of biological “race” is and the many ways it has nonetheless been used to excuse and promote bigotry and inhumanity, from India’s caste system to mistreatment of Aboriginal Australians to the colonizing of Africa. Decrying immigration by “people from shithole countries” is nothing new even for a president. In a recently unearthed tape from half a century ago, Ronald Reagan calls Richard Nixon to chortle about a U.N. meeting: “To see those — those monkeys from those African countries — damn them, they’re still uncomfortable wearing shoes!”

The thing is, though, if you set out from equatorial Africa and head north through Sudan to Turkey and then on through Ukraine and Latvia to Finland, you never hit a point where the people on one side of you are black and on the other are white. All you encounter are gradations shading into one another.

The genetic variants for skin color that Tishkoff and her team pinpointed arose long before any human ever ventured out of Africa. Her research indicates that some variants were carried away from there, then later reentered, then left again. With new discoveries of skulls and jawbones and other bits of hitherto unknown hominins in Australia, Israel, Greece, China, the picture now emerging is of human evolution, not as an upward-branching tree, but as a vine messily spreading out in all directions, circling back on itself, grafting, with branches forming and dying off and then sprouting again. White supremacists are essentially priding themselves on the latitude at which their ancestors took root.

We’re all of us mongrels. We can spit into test tubes all we want, trace our family trees back through the ages, but “purity” is antithetical to human identity. Genetics correlate to place, not race. According to a 2014 study of 23andMe customers in the American Journal of Human Genetics, the genetic makeup of African Americans averages 73 percent sub-Saharan African, 24 percent European and 0.8 percent Native American. The same study showed 3.5 percent of those who self-identified as “European American” likely had a black ancestor within six generations. The human pot’s been better at melting than we ever acknowledged, though often at terrible cost.

Early in the last century, the fashion in science was eugenics — the deliberate breeding of a superhuman race. That movement was always doomed by the genetic principle known as “regression toward the mean.” Two exceptionally tall parents are likely to have children who are shorter than they are. Moderately intelligent parents are more likely to give birth to an Einstein than are two geniuses. Evolution isn’t a relentless march toward perfection, and genetics are complicated. Sometimes a mutation that affects skin color may also alter eye color, or fat-cell distribution, or even susceptibility to infectious diseases. All the purebred beagles in the world still aren’t perfect beagles — and never will be.

In Superior, Angela Saini writes that the concept of race “is at its heart … the notion that groups of people have certain innate qualities that not only are visible at the surface of their skins but also run down into their innate capacities, that perhaps even help define the passage of progress, the success and failure of the nations our ancestors came from.” But culture, Tishkoff says, isn’t hierarchical. The fieldwork she’s done with remote indigenous tribes makes that clear: “What they’re doing to survive requires very sharp thinking. It’s not like my culture, but it’s very complex. They’re not some old remnant. They’re just not that different from us.”

Tishkoff’s most recent research is on San hunter-gatherers in Botswana — who carry that million-year-old light-skin variant — and East African hunter-gatherer tribes that speak similar “click” languages. The East African tribes appear to share common ancestry within the past 20,000 to 50,000 years but likely diverged from the ancestors of the San much earlier. And all these groups have continued to evolve; they haven’t just been treading water for hundreds of thousands of years.

I can’t help bringing up Tishkoff’s fellow Penn professor Amy Wax, who’s been in the news for a recent speech promoting white immigrants over those of color. Tishkoff gasps at my question — she has been out of the country — and googles frantically. “Oh no,” she says in dismay as Wax’s results appear. And no wonder. By and large, it isn’t people of color who’ve been shooting up America, just as it isn’t remote African hunter-gatherers who are melting the glaciers and strangling sea creatures with six-pack rings. It’s odd what we call progress. It’s even odder that “race” is easier to spot from a distance than in our genes.

Published as “True Colors” in the October 2019 issue of Philadelphia magazine.