Ancient DNA is helping rewrite human history

There are ethical and methodological pitfalls to avoid.

In universities and research labs across the world, scientists are actively rewriting whole chapters of human history, big and small. And they’re doing it using a very new piece of evidence: ancient DNA. That is, DNA collected and analyzed from a long-dead person. Scientists drill down into ancient bone, which, under the right conditions, can preserve genetic material for hundreds of thousands of years.

On this week’s episode of Unexplainable, we dig into all the ways this new form of evidence is turning human history upside-down: pointing toward a seemingly impossible journey people made from Greece to the Himalayas hundreds of years ago, giving us conclusive evidence that humans and Neanderthals had sex, and even suggesting there were more species of human-like hominids that have yet to be unearthed.

“We are in the midst of an ancient DNA revolution,” says Elizabeth Sawchuk, a bioarcheologist at the University of Alberta. “Everything we know from fully sequenced ancient DNA, we learned in the last 10 years.”

But while Sawchuk is excited about the possibilities of this research, and uses ancient DNA in her own work, she also sounds a note of caution. Ancient DNA is a minefield of potential ethical problems, she says, and when researchers rely too heavily on it alone, they run the risk of engaging in “molecular chauvinism” — assuming that DNA evidence is the only evidence that matters. Instead, ancient DNA is just one tool in our toolkit, and Sawchuk has some ideas about how to use it most responsibly.

This conversation has been edited for length and clarity.

Noam Hassenfeld

What makes it so exciting to work with such old DNA that’s been preserved like this?

Elizabeth Sawchuk

I think the thing that’s most exciting for me is that you have a direct connection to the past.

I study burials and all other kinds of situations where you find bits and parts of people from the past. We can study ancient tools, ancient technologies, pots, lots of things. But you never really get at the people who were actually there. And so with ancient DNA, we now have a new line of evidence on them.

You can look at that person’s ancestry — so who they’re descended from— and also their genetic similarity, so who genetically they resembled in terms of other people alive at that time and also people alive today.

Noam Hassenfeld

Are there concerns with how this technology is being used?

Elizabeth Sawchuk

Yes. Two big issues.

One: At the end of the day, you are destroying a part of an ancient person.

And then secondly, there are lots of interpretive issues as well. How do you take this new line of data and understand it with existing lines of data? And how can you put together a picture and a story that actually makes sense?

Noam Hassenfeld

Let’s start with interpretation. What are the issues with interpretation?

Elizabeth Sawchuk

Genetic sequences on their own are not that useful. DNA can’t tell you when a person lived. You need to know where the person was found, what the archeological context is.

At the beginning of the ancient DNA revolution, geneticists and archeologists and historical linguists and cultural anthropologists and all these other people, they didn’t necessarily talk to one another and didn’t really have the same vocabulary.

If you try to do these things in isolation, sometimes the stories come out a little bit wonky. And with DNA, there’s always kind of a tendency to draw these big maps with these big arrows of people moved here and mixed with these people. And that’s at times factually true, but it misses a lot.

Noam Hassenfeld

Is there an example in your work that you can think of?

Elizabeth Sawchuk

Absolutely. In 2019, we published a paper in Science about the spread of herding into eastern Africa. And in it, one thing we were looking for was the genetic variant for lactase persistence, so, the ability to drink milk.

Of the 41 individuals that we studied in this research paper, we were only able to look at that area of the genome for eight. And of those eight people, we only found that one person had the ability to digest milk.

That was a pretty amazing finding because, archeologically, we assume that if you’re investing so much time to take care of cows, you’re probably drinking milk. If you had only looked at the archaeology, you might assume they had the genetic ability to digest milk. If you only looked at the genes, you might assume that they couldn’t digest milk and therefore had no cows, which of course would not be the case.

So instead, we have a messy finding in the middle where they probably were drinking milk. But now we have to look to ethnographic data and cultural data to figure out how. And there are lots of ways that we know they can do this, for example, fermenting the milk. Or just be really farty herders.

Noam Hassenfeld

Is there something about the idea of DNA that lends itself to be seen as more factual than other types of data? I mean, I think in terms of forensics, sometimes we look at DNA at a crime scene and think, “Oh, that is definitely proving that this is a fact.”

Elizabeth Sawchuk

Yeah, I think I’ve heard it described as molecular chauvinism: that DNA is true above other things.

Noam Hassenfeld

So that’s the interpretation piece of this — we have to be careful not to weigh DNA too heavily as a tool, and to make sure it’s used in conjunction with other archeological data. What’s the ethical piece of this?

Elizabeth Sawchuk

Yeah, this could be definitely a whole episode, but I’ll try to keep it pretty brief. There are two kinds of main things that people are concerned about ethically.

One is that we’re destroying samples. So, once you sample a bone for ancient DNA, you are destroying part of it and you can’t ever take that back. There was a fear, which was pretty well-founded at the beginning, that without the protocols and the best standards to study these remains, what we were going to do is use them all up. We want to make sure that we preserve some for the future.

The second thing is dealing with the implications for the living. Up here in Canada, where I am, we have First Nation communities that are very involved in this. In the states, you have Native American communities. And of course, these are not monolithic groups at all. You have to put in a lot of effort to figure out who might be descended from the people you want to study and to involve them in the research.

There are real repercussions. I’m thinking about land claim issues, potentially. If you learn something about Indigenous populations, that might have implications in terms of their health and implications in terms of their cultural identity.

And then, most of these human remains were collected often in the 19th and 20th centuries in circumstances that we would no longer consider ethical. Today, the entire field of biological anthropology is built on bone rooms that were collected through colonialist means. So we have to consider, especially when human remains are not in their country of origin, how we would proceed to ethically sample those without doing more damage to potentially marginalized or minority populations.

(On the episode of Unexplainable, we discuss the use of ancient DNA to piece together the history of the skeletons found at Roopkund Lake in northern India. A recent analysis of these skeletons, which paired anthropological information with carbon dating and ancient DNA, revealed that some of the skeletons belonged to people who may have come from Crete.)

Noam Hassenfeld

So how does the Roopkund study fit into this framework?

Elizabeth Sawchuk

I think what I like so much about this study is that we can use these methods to tell these stories that are otherwise untellable, and then it gives life to a whole new range of questions and research topics that you can explore.

They had lots of good collaboration on this. They were looking at the remains from multiple different perspectives. They did a pretty good job of saying, like, this is what we know so far, but there are so many questions to still be resolved. And we need to look at both genetic and non-genetic evidence to try to resolve those questions.

Further reading

• Elizabeth Sawchuk digs further into the ethical ramifications of ancient DNA in The Conversation piece she co-authored, and lays out more of the results of her interdisciplinary herding research in a follow-up article. For more on the debates over ancient DNA, this guidance from the American Society of Human Genetics is very helpful.
• Later this year, Sawchuk will be part of a workshop taking place in Nairobi, Kenya, focused on ancient DNA research in Africa.
• In this episode of Unexplainable, we talk to Adam Rutherford. He’s the host of the BBC’s The Curious Cases of Rutherford and Fry podcast, and the author of A Brief History of Everyone Who Ever Lived: The Human Story Retold Through Our Genetics.
• If you want to read more on the Neanderthal-human history that has been teased out of ancient DNA, Brian Resnick’s piece on how we got things so wrong about Neanderthals is a great place to start.
• And finally, for more on the story of Roopkund Lake, which we also dig into in the podcast episode, check out Douglas Preston’s fantastic New Yorker piece on the subject, and the study in Nature that it is based on.