Ancient DNA is a powerful tool for studying the past – when archaeologists and geneticists work together

DNA has moved beyond esoteric science and into the center of everyday conversations about identity, culture and politics. It’s also reshaping stories about the past as advances allow scientists to extract ancient DNA (aDNA) from skeletons found at archaeological sites.

With each ancient genetic sequence, scientists learn new information about how people moved around and interacted in the ancient world. In some cases, this has helped overturn theories and resolve age-old debates.

But the aDNA “revolution” has also caused friction among geneticists, archaeologists and others over how this research is done. As archaeologists who collaborate on aDNA projects, we’ve witnessed these tensions firsthand. What lies at the heart of this rift, and how can these disciplines work together to better research humanity’s past?

What’s behind the aDNA revolution?

Ancient DNA changes how scientists do research, rather than the questions being asked. Geneticists are working on the same problems that archaeologists, anthropologists and linguists have wrestled with for decades, aimed at understanding transitions in the past and the roots of the modern world.

But instead of looking at things people left behind, geneticists are interested in the people themselves. Skeletons are the only direct connection to individuals who experienced life in the past. Biological anthropologists have long studied bones and teeth looking for clues about people’s origins and lives. Now, geneticists can look at their DNA – providing a new level of detail and insight.

The science behind aDNA is relatively new. The first fully sequenced ancient human genome – from a man who lived about 4,000 years ago in Greenland – was published only in 2010. At first this research was limited to skeletons from cold climates where DNA molecules are more likely to preserve. Success rates have steadily improved with cheaper and more efficient laboratory techniques and methods that target the most informative parts of the genome.

The part of the skull that houses the inner ear, called the petrous portion, has proven to be a particularly good source of aDNA. OpenStax College, CC BY
One of the most important breakthroughs has been the discovery that a small part of the skull – the bony casing around the inner ear known as the petrous – is a rich source of aDNA, even in poorly preserved skeletons from hot climates. This finding has led to a massive increase in the pace and scale of aDNA studies, with thousands of individuals sequenced in 2018 alone and sudden widespread interest in archaeological skeletons in museums throughout the world.

aDNA has thrust archaeologists and geneticists into new partnerships, where one side provides archaeological samples and questions, and the other additional questions, specialized labs and funding. These specialists, with different training and distinct work cultures, don’t always see eye to eye on study design, research pace or interpretation of results. Additionally, institutions and countries may not have explicit aDNA policies in place, leaving research teams and museum curators to navigate research and sampling protocols on a case by case basis. This has elicited concern from archaeologists, some of whom may worry the cart is so far beyond the horse that we should just cancel the trip.

But like radiocarbon dating in the 20th century, aDNA has already fundamentally changed archaeology and will only become more prevalent. Understanding current misgivings now is the best way to move the science forward in a way that benefits everyone.

Critiques of aDNA can be grouped into three categories: interpretive, ethical and systemic.

1) Interpreting the stories told by aDNA

Many concerns focus on how aDNA results are used to answer questions about the past. Most aDNA studies come from population genetics, a subfield that looks at major demographic changes over time – usually attributed to people moving or mixing with other groups, or both.

But identifying these processes doesn’t tell researchers why they happened or detect their impacts on culture. Some critics suggest geneticists construct sweeping regional narratives about migration and population change based on a small number of skeletal samples. Others point out that this research relies on naming and grouping ancient peoples based on cultural evidence like pottery styles, which may or may not reflect biological relatedness. Ancient genetic sequences are also usually compared to modern ones from living people, who have their own complicated histories and are grouped based on language or ethnicity or both at the time of DNA sampling, making for potentially problematic comparisons.

Ultimately, interpreting aDNA results involves many of the same archaeologically informed assumptions as other studies of bones, pots and tools. Yet the scientific aura of aDNA means findings are presented to the world through the media as more objective, stoking archaeologists’ frustrations over apparent “molecular chauvinism.”