As a shy undergraduate at Harvard University in the late sixties, Constance Hilliard butted heads with the stodgy chairman of the history department. Convinced that there were untold stories buried in her ancestry that could yield far-reaching insights, she told the prominent scholar that she wanted to major in African history. “But Africa doesn’t have a history,” she remembers him responding, indelicately defending his department’s lack of courses on the subject.
Not only does Africa possess a rich and varied history, it’s also the origin of all human history. Because the first Homo sapiens evolved there before migrating across the globe, our genome can be traced to the continent. Hilliard’s undergraduate years were marked by social upheaval, and she believed that a greater understanding of the interplay of the cultures and civilizations of Africa and the United States could help address many social issues.
Decades later, Hilliard, now a professor of history at the University of North Texas, in Denton, continues to pursue such lines of inquiry. In her most recent book, Ancestral Genomics: African American Health in the Age of Precision Medicine, which was published in April, she mines her decades of research to reveal remarkable findings about the genetic and ecological roots of some of the most persistent issues plaguing U.S. health care. She’s working to ensure that her discoveries have an impact on how medicine is practiced.
Hilliard sees a direct connection between gaps in historical knowledge and the medical community’s often imperfect understanding of African American health. As disproportionate mortality rates during the COVID-19 pandemic laid bare, the odds are often stacked against Black Americans. Higher rates of infant and maternal mortality, as well as of hypertension, diabetes, and death from heart disease, help explain why non-Hispanic white Americans live almost five years longer, on average, than their Black peers.
In Hilliard’s telling, doctors are failing to consider the ultimate cause of these disparities. “Too much time and effort is being devoted to arguing back and forth between whether medical science should be colorblind or whether it should focus on race,” she says. “Those two poles are a total waste of time.”
In 2008, while spending a year in the hilly coastal town of Nishihara, Japan, as a Fulbright visiting scholar, Hilliard experienced hip pain and went to see a doctor. The Japanese physician ordered a comprehensive medical exam, including blood tests, and concluded that the cause was arthritis. The condition was treatable, he told her, but he’d noticed something more troubling in the lab reports. “You appear to be suffering from kidney failure,” he said.
Yet when she returned to the U.S. a couple of weeks later, her primary care physician in Texas assured her that her organs were working fine. The test that alarmed the Japanese doctor had found elevated levels of creatinine, a chemical waste product left over from energy-producing processes in the muscles. But research has found that higher-than-average amounts of creatinine aren’t unusual among healthy African Americans. To account for this, medical testing in the U.S.—unlike in Japan—typically adjusts what’s considered the “normal” range of creatinine for Black patients.
“I was so relieved there was nothing wrong with me,” Hilliard says, “but at the same time, I was genuinely confused.” She had been teaching her students for decades that race is a social construct, but her doctor was saying that her race explained her diagnosis. Seeking answers, she returned to African manuscripts she’d studied as a young historian. “This was a narrative that could only be elucidated if a transdisciplinary approach involving historical and ecological knowledge was applied to the medical science,” she writes in Ancestral Genomics.
Hilliard had focused much of her early career on the important medieval trade center of Timbuktu, located in interior West Africa, in Mali. The city was home to a prosperous society that drew wealth from the exchange of gold and salt, along trade routes that extended from sub-Saharan Africa to Europe. Hilliard had pored over centuries-old texts from the region, translating and deciphering buried clues from the past. When reconsidering the material shortly after her 2008 misdiagnosis, she realized that “it is not the gold that offers insights into Black health but rather the commodity that was so desperately scarce in the African interior that its elites readily traded their gold to obtain it—salt.”
For countless generations before the gold-salt trade emerged, the humans living in this region had evolved to make do with a tiny fraction of the sodium consumed by their peers on the salt-rich coasts. Because the majority of Africans cast into overseas slavery came from the salt-poor interior of the continent, Hilliard writes, many Black Americans today likewise have much lower sodium needs—and stronger negative responses to a high intake of salt—than their non-Black neighbors.
It’s not the race of patients that doctors should take into account, she says; it’s their specific ancestry. (Indeed, race-based medical determinations have drawn criticism in recent years for not being based on sound science and for exacerbating health disparities.) African Americans whose ancestors hail from, say, coastal Nigeria might have elevated creatinine levels in the same way that they would have elevated melanin as compared with white Americans. But this group would be at a dramatically different risk level for kidney disease than those whose ancestors came from the salt-poor African interior.
Ancestral Genomics references studies that have consistently found salt sensitivities in African Americans, which—when paired with the salt-heavy contemporary American diet—have led to higher average blood pressures and increased rates of heart disease and kidney failure. The book traces these sensitivities to a variant of the APOL1 gene. Hilliard says that if, through genetic testing, medical professionals can identify patients who carry the variant, they can make dietary and lifestyle recommendations that account for the genetic predisposition. “Current medical research simply overlooks the unique ecological conditions of American Blacks’ genetic ancestry,” she writes. “Millions of dollars are allocated to studies that continue to attribute this population’s salt-sensitive hypertension and kidney failure solely to stress resulting from racism.”
As Hilliard dug further into the ecological conditions of interior West Africa, she came to her next big revelation. In parts of the region’s “tsetse belt” today, 99 percent of the inhabitants are lactose intolerant. The tsetse fly is endemic to much of sub-Saharan Africa, but particularly in West Africa the fly carries a pathogen that causes a wasting disease in cattle. Until recently, it was virtually impossible to maintain a healthy herd of cows there. “This harsh ecological environment accounts for the fact that West African food culture is devoid of dairy products,” she writes.
Prior research has shown that regions inhospitable to dairy farming fostered high rates of lactose intolerance among African and Asian populations, but such research tying ancestry to health conditions is relatively scarce. Hilliard learned that geneticists have identified a gene variant among those of African descent that may account for higher calcium retention and higher prevalence of certain cancers, including the aggressive triple-negative form of breast cancer and a severe form of prostate cancer.
Hilliard concluded that health disparities among racial groups in America may be explained, in large part, by inexact dietary guidelines for salt and dairy products. Rather than dividing patients into groups based on race, she argues, medicine should focus on what she calls ecological niche populations. Patients whose ancestors evolved in the same area will likely have similar genetic profiles and similar dietary needs and sensitivities. Hilliard writes that doctors should be equipped to consider such factors in developing recommendations on calcium and sodium intake, as well as matters such as kidney transplant eligibility.
Linda Dairiki Shortliffe, a Harvard classmate of Hilliard’s who went on to become a urologist and professor at Stanford University’s medical school, describes Ancestral Genomics as a revelatory book. It demonstrates, in a way she hadn’t understood before, that much of what we know about human health is based on the genetic data of those with European ancestry, which has resulted in a system of care tailored to one slice of the population. “I think the more that we find out about how both nutrition and drugs work, we’re finding that that is entwined with our basic genome,” she says.
While medicine is increasingly considering the distinct genetic profiles of individual patients, Debra Murray, a researcher in the molecular and human genetics department at Baylor College of Medicine, in Houston, concedes that “it’s a big issue” that hasn’t been adequately addressed. Hilliard’s book, she says, may help lead to improved medical guidance for patients of African ancestry. “The importance really is [in] treating people,” she says.
Shortliffe notes that clinical trials need to be run to test Hilliard’s recommendation that patients of interior West African ancestry should consider reducing dairy and sodium in their diets. She cautions that anyone who plans to make significant changes to what they drink or eat should first discuss it with their physician.
Meanwhile, Hilliard will set out on a book tour in October to discuss her research with health-care professionals who could implement the findings and with patients who stand to benefit the most. She’ll visit medical-research universities, public health schools, and historically Black colleges throughout Texas to deliver lectures and participate in discussions in service of a topic she’s calling “the hidden link to African American health.”
Her research has already informed her daily life and diet. She’s wary of overindulging in salt and dairy. We’re animals, after all, she says, and we evolved to live and eat in ways specific to the ecosystems our forebears inhabited. Much of her decades of research can be boiled down to a simple piece of advice: “Honor the staples and the food culture of our ancestors.”
This article appeared in the July 2024 issue of Texas Monthly with the headline “The Ancestral Roots of Health.” It originally published online April 16, 2024, and has since been updated. Subscribe today.
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