'Simply did not work': Mating between Neanderthals and modern humans may have been a product of failed alliances, says archaeologist Ludovic Slimak

Human and Neanderthal heads in museum display case.
A man looks at a Neanderthal women in these two reconstructions. (Image credit: mauritius images GmbH / Alamy Stock Photo)

Since the late 1800s, we've known that other types of humans once roamed our planet. At that time, scientists recognized that fossils unearthed in caves across Europe belonged to archaic humans now known as Neanderthals. Over that time, our understanding of Neanderthals has undergone dramatic upheavals.

In the early 1900s, scientists conceived of Neanderthals as apelike and almost bestial. But in the past few decades, unambiguous evidence has indicated that our closest human relatives mated with us at multiple points in time. Artifacts found at several sites suggest Neanderthals may even have had aesthetic projects.

Ludovic Slimak, an explorer and archaeologist at the Centre for Anthropobiology and Genomics of Toulouse in France, has been fascinated by archaeology since he was 5 and has spent more than 30 years hunting for our closest human relatives in caves on nearly every continent. He spoke with Live Science about his new book, "The Naked Neanderthal: A New Understanding of the Human Creature" (Pegasus Books, 2024), about why Neanderthals are not simply another version of Homo sapiens, what their mating with modern humans tells us about our first and last encounters with them, and what they reveal about our own human nature.

Editor's note: This interview has been edited and condensed for clarity.

Related: Read an excerpt from Slimak's new book, "The Naked Neanderthal"

Tia Ghose: How did you first become interested in Neanderthals?

Ludovic Slimak: I must have been maybe 18 years old. So very, very early, I spent a lot of time tracking this kind of human. I wrote my first book, "Naked Neanderthal," after more than 30 years of quest for those creatures.

[There's a] certain perception of a Neanderthal like a beast, or since 20 to 40 years [ago] in Europe, we have another perception of Neanderthals like another "ourselves." And I think, after working so many times on millions of Neanderthal tools, searching for them in caves everywhere, I think that all that was just wrong.

The important thing about this book is that, with my very precise knowledge of these populations, I use Neanderthals to try to understand what we are — us, sapiens on Earth. By defining "What is a Neanderthal?" in fact, I created this mirror that allows us to talk about us, and to define us and to understand what we are and where eventually we are going.

TG: The image of the Neanderthal when I was growing up was subhuman on some level. But in recent years, we've learned that Neanderthals and humans mated at multiple points. Not only did they mate, but obviously those offspring went on to have children such that our DNA has their DNA in it. How do you think that's changed our understanding of who they were? Or does it?

LS: We use the fact that — look, all sapiens today, to different degrees, we all have a certain degree of Neanderthal DNA — and [use it to say], "OK, so they did not disappear. We all came together, and we created a new humanity."

And, in fact, that's not what it's saying, the DNA, at all. When you are searching for ancient DNA [from 40,000 to 45,000 years ago] … all these early sapiens have recent Neanderthal DNA, and that's why we have [Neanderthal DNA] today. But when you reach and you try to extract DNA from the last Neanderthals, contemporaries of these early sapiens — let's say between 40,000 and 50,000 years ago — there's not a single Neanderthal with sapiens DNA.

Related: Are Neanderthals and Homo sapiens the same species?

And this is something incredibly important in terms of cultural anthropology, because the exchange of genes is never a love affair. In every traditional society, it's the question of the identities we are going to build between two groups, and that's what we call patrilocality.

When two populations are close to one another but they are very distinct — maybe they can have a different language and different traditions, they are in neighboring territories — they are going to exchange their women. That means that the women have the mobility; that means that my sister will go into your group …

TG: They come to a place to marry and have kids, right?

LS: … But if we do that, your sister will come into my group, and with that, we will become brothers, and we will come all together and become one larger and more powerful group. That's something universal in anthropology.

And we know also by DNA that this question of patrilocality, the mobility of women, was also the same thing for Neanderthals.

But when we see what happened at the moment of the contact, we see that all sapiens have Neanderthal DNA, and there's not a single Neanderthal with sapiens DNA.This is a major issue to understand the extinction and the precise interaction between the two populations.

Your sister, your Neanderthal sister, will come with me among my sapiens group, but my sister won't come with you. It's very rare, but it happens when there's a total war between two populations. And in that case, you consider that the other group are the transgressors of certain taboos and they are no longer humans. You will kill everybody, but you will keep the children, the women with you.

I don't say that there was genocide at all here between sapiens and Neanderthals. That could have happened in certain regions, but I don't think that's the process of extinction of Neanderthals.

What could have happened? I think that, OK, they have exchanged their sisters. But the genetic differences between the two populations were so important that then they must have tried and it did not work. And we know by DNA that when these two populations met together and they had children — and these children, if they were male, they were sterile or they couldn't survive. And so I think that the population tried a lot to exchange and to have alliances between the populations, and that simply did not work.

TG: So are you saying that all of the mating would have been between Neanderthal women going to Homo sapiens' communities, having female children, and then those are the only children who passed on their genes?

LS: It's very likely that we have a process that must work like that. But we also, of course, must keep in mind that our understanding, the value of ancient DNA, is very partial.

Archaeologist Ludovic Slimak has spent 30 years studying Neanderthals. (Image credit: Dr. Laure Metz)

TG: Are there any artifacts or discoveries that you think give clues about their culture?

LS: The first thing we must realize is that the archaeological data are very, very rich. If you're interested to understand "Who were the Neanderthals?" they left behind them millions and millions and millions of tools and weapons and flint elements. In fact, we have too much data, and we are not able to analyze everything.

But the problem we had when working on all these millions of objects is that each time, we don't really "see" Neanderthals.

I'll give you a very simple example so you can understand. You know that I found the very first Homo sapiens in Europe, continental Europe. I found remains that are older than 54,000 years old, while we [previously] thought that sapiens came 45,000 years [ago to Europe].

We have there, also, thousands of objects that were abandoned by these very early Homo sapiens. When we take these tools, they are made of flint [points], like the tools made by Neanderthals. When I analyze them, they are all the same. That means that if you saw a hundred of these points, and the 10,000 after that, they are all the same. If you take measures at 1-millimeter [precision], they are all the same.

But when, now, you're dealing with Neanderthal tools and weapons, there's something very important. Each of these are impressive. They are very nice, like the craft of the Homo sapiens. Each of these objects are completely different. That means that each object is unique.

It's as if the craftsman, the Neanderthal man, when he took the flint, the raw material, the boulder, he began to craft. But before that, he looks at the morphology, he looks at the texture, he looks at the color — and, according to that, is going to change his project. And every object will be unique. There's an incredible creativity there.

So what did we have at the moment of contact? It's not a supercreative Homo sapiens that encountered an inferior creature. We had what would have been the encounter of us, a superefficient creature, with them, a supercreative creature. This efficiency, the normativity, the uniformity is something major that defined Homo sapiens, and that's the message of my book.

There's something dangerous among Homo sapiens. I don't say that to say, "Homo sapiens is a very bad creature on Earth." The encounter between the Neanderthal and sapiens was not the encounter between good and evil.

It's likely that we were so efficient … [that] by our simple presence on the same territory, they have vanished like a wave. We were, we are, not evil. We are just what we are, biologically.

We are still this über-efficient creature. And actually, what we see is that we are destroying our planet, not because we are evil but because we are too efficient. We are destroying all the biodiversity not because we want to destroy the planet but because we can't do anything about our own way to be humans.

We can fight that. Our cultures can transform.

There's something in us which is very special, which is very dangerous. But we can change it, and we can only change it if we realize it and if we put words on it.

TG: How would you change it? What would be the things you would change about us to keep us from destroying our planet?

LG: In sapiens, there's a desire to do all the same thing, all together. Now what are we going to do with that?

If everybody wants to do the same thing all together in our own society, in our sapiens society, that also means that … the single person or a group of persons can change the world.

Editor's Note: This story was updated on Monday, Feb. 12 to remove an editor's note linking to research showing an early Neanderthal skeleton that contains some human DNA. Because that skeleton is from an earlier time period closer to when Neanderthals and modern humans first diverged, it does not have relevance to mating between Neanderthals and humans around the time Neanderthals went extinct.

 The Naked Neanderthal: A New Understanding of the Human Creature. Copyright © 2024 by Ludovic Slimak.

Published by Pegasus Books.

The Naked Neanderthal: A New Understanding of the Human Creature - $29.95 on Amazon

The Naked Neanderthal: A New Understanding of the Human Creature - $29.95 on Amazon

For over a century we saw Neanderthals as inferior to Homo Sapiens. More recently, the pendulum swung the other way and they are generally seen as our relatives: not quite human, but similar enough, and still not equal. Now, thanks to an ongoing revolution in palaeoanthropology in which he has played a key part, Ludovic Slimak shows us that they are something altogether different -- and they should be understood on their own terms rather than by comparing them to ourselves. As he reveals in this stunning book, the Neanderthals had their own history, their own rituals, their own customs. Their own intelligence, very different from ours.

Tia Ghose
Managing Editor

Tia is the managing editor and was previously a senior writer for Live Science. Her work has appeared in Scientific American, Wired.com and other outlets. She holds a master's degree in bioengineering from the University of Washington, a graduate certificate in science writing from UC Santa Cruz and a bachelor's degree in mechanical engineering from the University of Texas at Austin. Tia was part of a team at the Milwaukee Journal Sentinel that published the Empty Cradles series on preterm births, which won multiple awards, including the 2012 Casey Medal for Meritorious Journalism.