What can dental plaque tell us about our ancestors?

As small children, we learn the importance of brushing and flossing our teeth. But as it turns out, a little tartar may be a good thing, at least for anthropologists studying early modern humans. Plaque contains genetic information that offers clues about how early humans lived millions of years ago. Professor Christina Warriner, a pioneer in the field of oral microbial ecology, joins Hari Sreenivasan to discuss.

TRANSCRIPT

As small children, we learn the importance of brushing and flossing our teeth, but, as it turns out, a little tartar may be a good thing, at least for anthropologists studying early modern humans.

Plaque contains genetic information that offers clues about how early humans lived millions of years ago.

Joining us is Professor Christina Warinner, a pioneer in this field of study.

I didn't even know that it existed until we were preparing for this conversation.

Oral microbial ecology?

Microbiomes from people that used to live 1,000 -- How do we figure out what people 1,000, 2,000, a million years ago ate?

It's a great question.

And, actually, we've only started to unravel this in the last couple of years.

It's only with recent advances in genetic technologies that we can even do this work.

So the field's very, very new.

But it turns out there are two substrates that preserve in the archaeological record, which give us insights into our ancient microbiome.

One is paleofeces, or preserved human feces.

They don't preserve very often.

They mainly preserve in things like very very dry contacts, like dry caves or underground mines, for example.

The other one is a little bit more common and, I think, quite interesting, and that's dental calculus.

Although, most people might know it by its other name, dental tartar.

This is calcified plaque on the surface of your teeth.

It preserves just like the rest of the skeleton for tens of thousands of years.

So, when you're scraping that, what could you possibly get out of that plaque that helps you figure out something about the person or the environment that they lived in?

It turns out that calcified plaque is like a time capsule that retains all sorts of things that you put in your mouth over the entire course of your life-span.

So, we find an amazing diversity of things.

We find human DNA from yourself.

We find dietary DNA and dietary proteins, as well.

Also, plant microfossils, tiny starch granules, phytolites, which are a type of plant glass, pollen granules.

We find all sorts of information in addition to the bacteria themselves, who lived on your teeth or transiently passed through your mouth -- for example, when you had a respiratory infection.

Wow. Okay.

So, the importance of brushing.

So, obviously, these people didn't brush, and that's why they had this build-up, right?

Yes.

So, is there a surprising discovery that you didn't expect in somebody's mouth or on their teeth?

We have had so many surprising discoveries.

One was -- until a few years ago, no one thought that anything was really even retained in dental calculus.

It was widely believed to have no DNA and no proteins.

We now know it's actually the richest source of ancient DNA and proteins known in the entire archaeological record.

We get as much DNA out of dental calculus as we can from fresh human liver, for example, which is one of the richest sources of DNA in the human body.

We've learned all sorts of information.

So, for example, one surprising discovery, for me, is -- we were looking at dental calculus from different populations around the world.

And I was focusing on Norse Greenlanders.

These are the famed Norse Greenlanders who died out in their colonies during the medieval period.

And we started seeing milk proteins over and over and over again.

And what we realized was -- dental calculus actually preserves traces of milk consumption.

Milk is otherwise almost entirely invisible in the archaeological record, as you might imagine.

It spoils very, very quickly.

And so we know very little about the origins of dairy and how it spread throughout the world.

We can now go back to specific time points in the past and tell if someone -- a particular individual -- drank milk or not.

And we've applied this throughout Europe and we're now starting to apply it even further back in time and into the Middle East to try to understand when people first started changing their use of livestock from just for meat and hides to also incorporating dairy.

When you're saying that you can figure out when people drank milk, you can also figure out what kinds of diets they were on, right?

So there was, obviously, the fad a few years, the Paleo diet.

Mm-hmm.

'Let's go back to eating like cavemen and cavewomen.'

Are we actually doing that?

Were they eating the same thing?

The popular Paleo diet is a little bit different than what people actually ate in the past.

It's actually almost impossible for us that live in modern, industrialized societies to eat like our Paleolithic ancestors, and that's because our foods have been so incredibly, radically changed by the process of domestication during agriculture.

There's very few foods in a grocery store that you can buy that's truly from the Paleolithic.

Probably the only thing that you could find would be something like wild-caught fish.

Everything else is a product of agriculture.

We can learn from what our ancient ancestors ate and take some lessons from that.

It's clear that what they ate were fresh foods, in season.

They had a high degree of roughage and fiber.

All of those things are dietary components that we are evolved to eat and are quite healthy for us and promote good, healthy bacteria in our bodies.

All right, so, let's talk about that bacteria.

We've had conversations about the gut bacteria before on this program.

But how has that changed over time?

That's a great question, and it's one that we have an active research project on right now, looking at paleofeces specifically to try to understand these changes.

But what I can say is -- our research group at the University of Oklahoma has been focusing on this question, and we recently published a study where we looked at this question of, 'To what degree does subsistence, the type of diet you have, affect your gut microbiome?'

And this study was conducted on three populations -- the Matsés, which are a hunter-gatherer group in the Peruvian Amazon, the Tunapuco, who are a traditional agriculturalist society that lives high up in the Andes Mountains, and Americans living in urban cities.

And what we found was that the traditional societies -- it doesn't really matter if they're hunting and gathering or traditional agriculturalists, they have quite a similar gut microbiome.

Where we see a tremendous difference is in industrialized societies.

This suggests to us that although agriculture and this transition from the Paleolithic to the Neolithic had some impact on our gut microbiota.

The huge change has likely been much more recently.

So, our teeth might be shinier because we have all kinds of toothpaste and whatever, but what's happening inside might be very different.

That's right.

Where we're kind of focusing on right now is -- it appears that many of these changes that have occurred in our gut microbiome and our microbiome more generally are probably on the order of the last few centuries and don't necessarily stretch all the way back 10,000 years ago.

So, this makes it a little bit easier to eat a healthy diet.

We don't need to go back 10,000 years, even just a few centuries, taking some notes from our more recent ancestors could be very helpful for improving our health.

All right, Christina Warinner, University of Oklahoma.

Thanks so much.

Thank you.