What having Neanderthal DNA means for modern people

Scientific evidence proposes that most humans, to some degree, are a little bit Neanderthal.

While anthropologists long speculated that Homo sapiens and Neanderthals mated, this interbreeding wasn’t confirmed until May 2010, after the Neanderthal genome was sequenced and compared to modern humans.

It was then, only a decade ago, that people became aware of the possibility that Neanderthal DNA lived in them — all they needed to do was take a look at their own genetic material.

The biotechnology company 23andMe made this possible in 2011 when it started offering “Neanderthal ancestry insights.” You could see the variants in your DNA that traced back to Neanderthals and compare your percentage of Neanderthal DNA to other customers who used the service.

In April, 23andMe issued a new Neanderthal report based on the mountain of new customer data it had accumulated. (The company says it has more than 12 million customers, with more than 9.6 million opting in to participate in its research.)

More customers, new Neanderthal discoveries, and advancements in genetic research have meant a clearer assessment of who the Neanderthals were and what that means for the people who harbor their legacy in their DNA.

For 23andMe customers, this meant that the number of their Neanderthal DNA variants, and the percentage of their DNA that is Neanderthal, have likely changed.

The new list of Neanderthal trait variants correlates to behavior that feels especially relevant in modern times, like being less likely to be afraid of heights, more likely to be a hoarder, and more likely to have a fear of public speaking.

Inverse recently spoke with Samantha Esselmann, Ph.D., the 23andMe product scientist behind the new report. Esselemann explains what's new in Neanderthal research and why they were probably a lot like us.

This interview has been edited and condensed for clarity.

How is this new report different?

All of the exciting Neanderthal science that’s happened outside of 23andMe in part inspired me to do this report. There’s also been a lot that happened and 23andMe that’s helped us provide new information.

Since we created the first report, we have millions of more customers. This means that those genome-wide association studies that look for associations between variants and traits now have improved statistical power to detect those associations. Our understanding of the list of Neanderthal DNA variants hasn’t changed. But, when we updated our genotyping chip to the most current version, we were able to identify a different, but somewhat overlapping set, of DNA variants that we probably inherited from Neanderthals.

The underlying snips, or variants, that we tested for on the new chip are more representative of global variation. Before, it was a bit more biased toward European populations.

For example, in the old chip, Northern Europeans often had the most Neanderthal DNA variants that we were able to identify on the chip. But now people of East Asian descent tend to have more Neanderthal variants. That was pretty cool to see, because if you squint and look at the data, it’s maybe consistent with some published research that suggests a two-pulse model of Neanderthal ancestry for people in East Asia.

Of the human traits associated with Neanderthal variants, are there connections that you find interesting? When you come across the list one might think they are kind of wacky, yet still, ring true.

I think a lot of them do seem on the surface pretty silly — like being slightly less likely to be "hangry," or being more likely to be a hoarder. It is kind of hard to take those very modern terms and modern ideas and try to make that connection back to Neanderthal DNA and how that might influence how you behave.

There are some of these associations that fit some of our preconceived ideas about Neanderthal behavior or what they look like. The ones that are especially cool break down those stereotypes. For example, a variant associated with being less likely to be hangry, or being less likely to have a fear of heights. I think these are interesting because they break the mold.

On the flip side, one interesting example that fits our idea of what they looked like is that we found a few DNA markers are associated with having a bit of an apple body shape — rather than a pear shape. Again, if you squint a little bit, that’s consistent with what we know about Neanderthal stature. The skeletal remains of Neanderthals that have been found appear to have a more robust body with a barrel-shaped chest.

It seems like 23andMe has a lot of people talking about Neanderthals when they probably wouldn’t have. How does that speak to your mission when it comes to creating reports like this?

For me, updating this report was a love letter to Neanderthals. I went into it with the goal of destigmatizing this other human population. There’s a lot that we can’t yet say about how this DNA affects your health or biology. It was more, for me, about highlighting this really special connection to basically our closest evolutionary cousins, who went extinct 40,000 years ago.

I thought it was so cool personally that their DNA is in us and it kind of shifted my perspective. I wanted to share that with people.

It starts to make you ask some really interesting questions, like, "What even is a human? What would it have been like when we weren’t alone on the Earth? If I met a Neanderthal today, would I think they were cool?"

Speaking of destigmatizing — Neanderthals used to be thought of as “dumb” humans. Now we know they were like us in many ways — they created art, they had rituals. Do you think we’ll continue to learn more about them?

Totally. Outside of 23andMe, in academia, there’s a lot of work looking at how Neanderthal DNA could affect our health. We don’t get into that in the report, but there’s a lot of work looking into how Neanderthal DNA might affect our immune systems.

Especially now with this global pandemic, it’s interesting to think about how interbreeding with a closely related population, whose immune systems had experienced a slightly different set of stressors, might have helped our human ancestors adapt to a new environment.

There are some really interesting examples of how scientists are trying to tease apart this question of what makes us human — which is, now that we have a Neanderthal DNA sequence, comparing that to humans, trying to look for those differences.

"We can’t just so easily dismiss them as grunting dummies anymore."

I think the more I was doing research for this report, the more I kind of got annoyed by this question of what makes us human? I think I felt that because Neanderthals were human. Every week, we are learning something new about what they were capable of. We used to think they were dumb, bad at hunting, not creative; couldn’t talk. Now, it feels like every week there’s some new crazy discovery about what they could do. We can’t just so easily dismiss them as grunting dummies anymore.

I think as humans, we’ve approached the study of our more recent evolution with an assumption of superiority, but the reality is way more complex. I think this story will continue to be rewritten and the line between humans and Neanderthal will become more and more blurred.

Honestly, at the end of the day, I wouldn’t be surprised if it becomes easier for us to answer that question “what makes us human” by looking for similarities with Neanderthals rather than differences. I think they were a lot like us.