A lab technician reaches one hand into a sealed and sterile chamber to grasp a sandblasting tool. Inside, his other hand gently holds a 4,000-year-old skull fragment no larger than an oreo cookie. Precisely, he zeroes in on the genetically rich cochlea, a spiral chamber of the inner ear. After removing the surface of the bone, he will grind the tiny cochlea into a homogenous bone powder, a material found to yield up to 100 times the amounts of DNA gathered from teeth or other bones.
David Reich ’92 is a professor of genetics and principal investigator at Harvard Medical School’s Reich Lab. He is also the winner of the 2019 National Academy of Sciences Molecular Biology Award for his work in the field of ancient DNA. His team’s large-scale sequencing of ancient DNA has revealed hard data about who we are genetically and historically, interrogating aspects of how we are all related to each other. David’s background expertise in medical genetics allowed him to vastly improve efficiencies in ancient DNA analysis and subsequently—as with the invention of the microscope centuries ago—this new scientific instrument is revealing astounding truths about ancient human populations living in a world previously invisible to us.
David explained, “The newfound ability to measure the way people are related to each other and to people living long ago makes it possible to pursue questions directly about human interactions in the deep past. We can study the changes that are perceived in the archaeological record and identify what movements of people—or lack of movement of people—correspond to these changes. What the genetic data are showing again and again is that prevailing consensus is often profoundly wrong. Frequently, what we find from ancient DNA lies outside the realm of what the great majority of archaeologists and anthropologists believed was most plausible. The work presents challenges to traditional understandings of the nature of how human populations interacted with each other in the past.”
David’s primary aims at present include promoting cross-disciplinary cooperation between geneticists and archaeologists, and publishing analyses of population history based on the 6,000-plus individuals for whom he and his colleagues have generated genome-wide data.
In 2013, the year his lab opened, the total number of published ancient genomes was 14. By 2015, they had passed 100, and by the beginning of 2018, they had passed 1,000. “In our laboratory alone, we have generated more than 6,000 sequences of ancient people; most of them are unpublished and generated only in the last couple of years, and we are working to bring them to publication. The number of published sequences by our lab and others has been increasing rapidly—more than 100-fold in five years.”
To date, the Reich Lab has generated slightly more than half of the world’s data. David’s 2018 book, Who We Are and How We Got Herepop, introduced the wider academic community—and the public at-large—to the field of ancient DNA.
“I decided to write a book without jargon that would be useful for humanists, historians, sociologists, and archaeologists who wanted to come to grips with this new scientific tool. Its primary audience was other scholars including students, like many of the ones at GDS, who are interested in these topics. My lab reflects my own peculiar mixture of interests in history, social studies, human relationships, and also in the hard sciences—interests that were already manifesting themselves at GDS.”
“David was absolutely brilliant in math, anything STEM, and in my field of history,” said history teacher Sue Ikenberry. “Because other classmates were also outstanding in academics, that time period was the making of him. He learned how to work with other incredibly smart people and get his voice heard without alienating others.”
“Sue was a particularly important teacher-mentor to me, and her mentorship helped me to flourish,” David said. “She had an academic, critical approach that introduced me to alternative ways of thinking about the past and how things work.”
“I think the eclectic nature of the School and the broad curriculum probably helped David develop a sense of the use of history and the breadth of it,” Sue explained. “The 11th grade course, for example, encourages students to consider different perspectives of historical events. For a lot of kids this focus is particularly exciting, and I think it was for David. When you look at his work, which is so technical and yet so historical, you can see how that class could have served as an influence in him realizing that his strengths in STEM and history could in fact be combined, which is exactly what he has done in a remarkable way.”
In the global community hard at work in this field, David has found enormous value in collaborations, especially those across significant lines of difference.
As just one of many examples, David and his colleagues have recently published a study of the people who first practiced herding in East Africa—a project made possible through an interdisciplinary collaboration with archaeologists, many of whom have spent their entire scientific career on this work. “The genetic data in some cases agree and in some cases are in tension with archaeological explanations. Genetically, the first herders of Kenya and Tanzania derived 40% of their DNA from ancient peoples who came from Northeast Africa around 5,000 years ago and were rather closely related to people who lived in the Middle East around 5,000 years ago. It raises the question, ‘Where does this DNA come from?’
“It is easy to jump to the conclusion that this DNA derives from farmers or herders from the Near East who migrated to Africa, but an alternative—and entirely possible—scenario is that this DNA traced to ancestors who lived entirely in Northeast Africa for many thousands of years; we just won’t know until we get ancient DNA from places like Egypt and Ethiopia from that period. In parts of Africa, there is appropriate concern about falling into a trope that suggests important innovations traced their origins to human migrations from Europe and the Middle East, when in fact we know of many counterexamples where there were spreads of people and ideas in very different directions. We had to develop language that is sensitive to those discussions. Together with archaeologists and anthropologists, we are coming up with vocabulary that can help form the basis for effective communication among geneticists, archaeologists, and anthropologists. Use of words like populations, which is a bland term in genetics, is a more fraught word in anthropology, and we geneticists need to understand that when we use the word. Or, archaeologists will ask, ‘What is the identity of these ancient people?’ And we’ll ask, “Well, what does identity mean? Is this a genetic concept or a cultural one?
“Even though we geneticists are not trained in the language that archaeologists use, we and they are working hard to learn to speak each others’ languages better. This is a constructive dialogue that will eventually help all of us to get to a better place and to understand the world in a richer way.”
David explained that some of the criticisms that have emerged as a result of this work reflect the tensions that come about with new knowledge. Still, these are the sort of rich discussions that David welcomes. The team specifically seeks out topics where there are unresolved major questions—even where others see these topics as too controversial for study—and aims to address them with cross-disciplinary collaboration, which becomes increasingly important as the data erode some of the false, simplistic constructs society uses to frame how we talk about differences among people.
He said: “It’s no longer defensible to say that there are no meaningful differences amongst human populations or that there is not enough time in human evolution for any differences to have developed that would affect traits we care about. Genetics has shown that not to be the case. Genetics has also shown that while the average differences that exist among people in different groups are very small relative to the differences we might see among a typical pair of individuals in a classroom, they are there. We need to develop the sophistication to talk about the genetic differences among individuals and a tolerance as a society to understand that people are different from each other genetically. We must deal with human diversity in its genetic manifestation just as we strive to deal with diversity in people's cultural backgrounds.”
The response to David’s work has stirred up strong emotions and reactions. A cover article in The New York Times magazine on January 20 argued that David’s work was revolutionizing our understanding of the past but at the same time was “indistinguishable from the racialized notions of the swashbuckling imperial era.” David replied in a letter to the editors saying: “Ancient DNA findings have rendered racist and colonialist narratives untenable by showing that no human population is ‘pure’ or unmixed. It is incumbent on scientists to avoid advocating for simplistic theories, and instead to pay attention to all available facts and come to nuanced conclusions. The same holds true for journalists reporting on science.”
The rapid increase of visibility to the field of ancient DNA reflects the growing appreciation for the statements David and others’ findings make about the past. “We are just at the beginning of this field.”
Over the next five years, a $15.5 million funding award for the “Ancient DNA Atlas of Humanity” from the John Templeton Foundation to David’s lab will make possible a 10,000 genotype-strong ancient DNA database, gathered painstakingly from 10,000 grains of bone.
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