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“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. “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.”

“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.” The rapid increase of visibility for 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.



Profile for Georgetown Day School

Georgetown Days Spring 2019  

Georgetown Days Spring 2019