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Homo sapiens aren't as unique as we once thought. In fact, only about 1.5 to 7% of our DNA originated in our species alone. Everything else we share with our ancestors and those human species we coexisted with, including Neanderthals,
New genetic discoveries reveal Homo sapiens share most DNA with ancient human species, reshaping our understanding of human evolution.
Key Takeaways
- Homo sapiens are not genetically unique; most of our DNA comes from archaic human species.
- Interbreeding with Neanderthals, Denisovans, and ghost populations shaped modern human genomes and adaptations.
- Recent genetic changes unique to Homo sapiens are concentrated in brain development genes.
- Ancient DNA provided evolutionary advantages but also introduced health trade-offs.
- Human evolution is a complex, intertwined story rather than a simple replacement of archaic humans.
Summary
- Homo sapiens share only 1.5 to 7% of DNA unique to their species; most DNA is inherited from ancestors and other human species like Neanderthals and Denisovans.
- Interbreeding between Homo sapiens and other archaic humans left lasting genetic legacies that influence modern human biology and adaptation.
- Svante Pääbo’s sequencing of Neanderthal DNA in 2010 revolutionized paleoanthropology and earned him a Nobel Prize.
- Denisovans, discovered from a finger bone in Russia, represent another archaic human species contributing up to 5% of DNA in some modern populations.
- The small percentage of unique Homo sapiens DNA clusters around genes involved in early brain development, suggesting recent evolutionary changes in neural wiring.
- Modern human genomes have evolved significantly over the last 300,000 years, especially in the last 10,000 years with agriculture and increased trade.
- Ancient DNA contributed adaptive advantages, such as improved immunity and temperature regulation, but also biological trade-offs that affect health today.
- Ghost populations of ancient humans are detected in modern genomes, indicating unknown archaic human species contributed genetic material.
- The traditional 'Out of Africa' model of human evolution is challenged by evidence of interbreeding and genetic mixing with archaic humans.
- Our genetic heritage is a complex mosaic, with Homo sapiens being the current outcome of a long history of inter-species interactions and adaptations.
Chapters
- 00:00Introduction: Rethinking Human Uniqueness
- 02:08Ancient Encounters and Genetic Legacy
- 04:08Denisovans and Genetic Contributions
- 06:02Human Genome Evolution Over 300,000 Years
- 08:02Unique Homo sapiens DNA and Brain Development
- 10:06Interbreeding and Its Biological Trade-offs
- 12:46Revising the Out of Africa Model
- 18:56The Complex Story of Human Origins
Full Transcript — Download SRT & Markdown
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Denisovans, and even something we like to call ghost populations. This rewrites the story we have told ourselves about our species. We just aren't that unique.
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For a long time, we believed Homo sapiens were the special ones, the human species that outcompeted and replaced everyone else. But modern genetics has revealed something much stranger. When our ancestors met these other species, they did not just compete with them,
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they mated with them. And those encounters left a permanent record in our DNA. In other words, those ancient humans we thought had vanished did not necessarily disappear. Some of them are still here inside you.
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When you're looking at the sort of biblical account of where humans came from, you're looking at an account that says that humans had a single origin and everybody fits within that very common frame. And then they introduced these
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other people, right? And there, like east of Eden, there were these other people who were unexplained within our actual story. When you say that I'm 2% Neanderthal, what that means is that there were groups of people that were
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separated for 800,000 years from each other that in the end came back together and found a way to make it work. And that's kind of wild, right? We, we, that's a story that our histories don't give us.
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We have been reporting on ancient human origins for decades here at New Scientist. And today we are bringing our experts together to explore the discoveries that are rewriting the story of our species. From a 90,000-year-old girl with fascinating hybrid DNA to
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those ghost populations I mentioned hiding in our own genome. We will uncover how these ancient encounters gave us the genetic tools that may have helped us conquer the planet. But these ancient encounters did not just shape how we survived. They're still shaping
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how our bodies work today. Sometimes in ways that help us and sometimes in ways that actually hurt us. Think about it.
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Our ancestors entered a new environment where another species of human had already spent hundreds of thousands of years evolving to the local conditions, evolving immunities to the local parasites. Picking up some of their DNA was a bit like accessing a cheat code,
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but it did not come for free. It came with biological trade-offs, and we may still be paying the price for that today.
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Chapter 1, the discovery that rewrote human evolution. Our story begins in 2010. For a century, paleoanthropological research was largely limited to stones and bones. But when evolutionary geneticist Svante Pääbo successfully sequenced Neanderthal DNA, he revealed a truth that rewrote our
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identity. Something so big he won a Nobel Prize for the research. People outside of Sub-Saharan Africa and some within carry roughly 2% Neanderthal DNA inside their bodies. These ancient humans weren't just rivals. They were partners.
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People like Neanderthals and Denisovans interbred with us. So, they haven't gone completely extinct. A bit of them lives on in us, in our DNA. That's made a big impact.
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That same year, a finger bone from a Russian cave revealed a third player, the Denisovan. Our family tree was becoming a bit more crowded. More surprises were to come. It turned out that some people today carry Denisovan DNA
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in their bodies. Up to about 5% in the case of some populations in East Asia.
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2% Neanderthal DNA, 5% Denisovan DNA. Let's take a minute to ask what exactly that means. Now, you might have heard that we share 98% of our DNA with chimpanzees or even 50% with bananas.
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This isn't the same thing. Those numbers indicate how we evolved from a common ancestor millions or even billions of years ago and still use similar systems and proteins. But if we're talking about how similar our DNA is to Neanderthals,
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it's more than it is with chimpanzees and certainly with bananas, let me tell you. The DNA from the Neanderthals, that 2%, and the 5% from Denisovans, that's because of interbreeding with them. Now, you might think 2% is really small, but
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think about it. About 50% of the DNA in your body comes from your mother and another 50% from your father. And as you go back in time through your family tree, the number of your ancestors grows with each generation. So, you have four
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grandparents, eight great-grandparents, and so on and so forth. This also means that the amount of DNA inside you that specifically came from those more distant ancestors is smaller. You have to go back a lot of generations before you find any Neanderthals or Denisovans
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in your family tree, but they are probably there. And remarkably, a few tiny snippets of the DNA that those ancient humans had in their bodies still survive inside yours today. Enough to make up about 2% of your genome when it
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comes to the Neanderthals. Okay, now we've cleared up that puzzle. Let's think about the inheritance question in a different way. There's some debate over exactly how long our species Homo sapiens has been around, but it's safe to say that we've been around for at
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least 300,000 years. And over those 300,000 years, human genomes have been evolving. Slowly but surely, the DNA they contain has changed. When we look at populations around the world today, there have been huge genetic changes that have unfolded in the last 10,000
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years as people became agriculturalists, as they established greater trade links between very different people, and those changes have made a big difference.
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This means there are some DNA sequences in our body that are unique to our species, Homo sapiens. These aren't the DNA sequences we inherited from ancient ancestors. They aren't the DNA sequences that we inherited from the Neanderthals or Denisovans through interbreeding.
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These are sequences you will only find in Homo sapiens because they changed after we split from other species of human. Think of our genome as a massive book. We used to think we wrote the whole thing ourselves from beginning to
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end and we just borrowed a few sentences here and there from the Neanderthals. Most of our book, it turns out, is actually plagiarized.
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So, how much of our DNA falls into this category? In 2021, Nathan Schaefer and his team at University of California, San Francisco came up with a way to answer that question. They developed an algorithm known as SARGE, the speedy
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ancestral recombination graph estimator. Schaefer's team examined the DNA from Vindija, two Neanderthals, and 279 very lucky modern humans. Their conclusion: a surprisingly small amount of our genome is truly just us. In fact, maybe just 1.5 to 7%.
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For the most part, we're 98% the same as chimpanzees. The things that make us human, we know, are a small fraction of our overall DNA. Within that small fraction, the things that actually mattered, the things that we can track
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down and say, "Oh, yeah. This series of genetic changes made us into a language-using species that is more inventive and more creative and is more social and more tolerant of being around other people. All the things that make
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us human." We don't know yet what they are, but we are increasingly able to find the things that did change.
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SARGE also revealed that these slivers, these DNA fragments that are uniquely Homo sapiens, weren't scattered randomly.
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They were clustered around genes for early brain development. Specifically, the development that happens before we're even born. In other words, Homo sapiens is far from a wholly new model.
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Our bodies are overwhelmingly made of basically recycled parts. This ancient DNA isn't just a handful of leftovers or a biological souvenir from the past. It is the vast majority of our living blueprint. But the regions governing our neural wiring, how our neurons connect
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in the developing brain, received a very specific and very recent proprietary software update.
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small uniquely human spark. Chapter 2. When humans first met other humans. For decades, the out of Africa model was by far the dominant theory. It held that homo sapiens evolved in isolation in Africa and then the big bad new kid on
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the block, us spread across the world and simply replaced everyone else. We now know the story is wrong. When our ancestors crawled out of the evolutionary cradle 300,000 years ago, there were as many as six other human species coexisting. Instead of just out
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competing their rivals, Homo sapiens merged with some of them. Every piece of evidence that we have from ancient genetics today tells us that against all odds, people made it work with with other populations that were really different from them. What we know then
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is that homo sapiens reemerge from Africa. Um, and maybe 60,000 years ago, a small group of homo sapiens came out moving into the territory of Neandertos.
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There was then some interbreeding with Neandertos. And as those homo sapiens populations spread out across the rest of the world, they took that little bit Neanderthal with them.
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These encounters left a map in DNA. Because we met Neanderthalss in Western Eurasia, all people with ancestry in Western Eurasia, carry Neandthal DNA inside them. When Homo sapiens spread further east, they met the Denisans, which is why some people, particularly
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those with East Asian ancestry, have denisant DNA in their bodies. And those are just the groups we've named. Genomes from modern populations in Africa hold the genetic signature from unknown, unidentified archaic hominins, ghost DNA. Now, you might be thinking, "Oh, so
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it sounds like if you're from outside of Subsahara and Africa, you have some DNA from these other ancient human species, but if you're from within subsahara and Africa, you only have Homo sapiens DNA." Not quite. Those ghost lineages we were
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talking about, those ghost populations, well, they tell a kind of fascinating story. It turns out that there are some populations within West Africa that have ghost DNA. And that means that when the geneticists have looked at their DNA,
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they have seen that the source of the DNA in some populations, specifically the Europa and the men come from a source that is not homo sapien. It's not Neanderthal. It's not Denisan. It's basically no human species that we have
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the genetic material of. It comes from a different ancient human species. We call those ghost lineages because we just have no idea who they are. They exist.
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We see their signature, but we don't know the origin of it. It might be that it's one of the species that already exists that we know of. So, for example, Hermoni in Africa or Hermohalenzis that we know of in Africa. But we can't be
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sure because we still don't have DNA from either of those two species. But what we do know is that that DNA seems to have originated around 600,000 years ago, probably before Neanderthals existed, which blows my mind because it
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means that interbreeding with ancient human species was kind of ubiquitous for our human species. Homo sapiens were constantly apparently on every continent having sex with other species. In short, there was no single line of ancestry leading to where we are today. Through
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our migrations and over millennia, via gene exchange, modern humans gradually coalesed into a composite of multiple ancient human lineages. We are a mosaic species.
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It's again and again finding ways to to come together. And to me that is really the story of genetics right when we say what's the evidence that we came from some small number the evidence is that every time we try to trace our
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genealogies they intertwine. This mixing and remixing radically changed our biology. It's why we are a mosaic. In many cases, the individual archaic threads woven into the genetic fabric provided a vital function, a sort of genetic cheat code. In some cases,
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these genetic gifts continue to serve us well into the present day. We humans really think we are special and we have come to dominate the world around us, build civilizations, explore the universe, and share our knowledge with each other, including here on YouTube.
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But clearly we are just the current pinnacle of a long history of curious individuals thinkers explorers and dare I say it, scientists. It's exactly this quest for a better understanding of the world around us that New Scientists has been exploring since 1956.
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Their journalists and editors have worked with researchers across disciplines to explore not just what we know, but what we don't know yet and why that matters. From human origins and ancient cultures to breakthroughs in physics, space, and technology, they
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focus on the ideas that reshape how we understand the universe and our place within it. If you want to go deeper than a single story, a new scientist digital subscription gives you access to all of this award-winning science and
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technology journalism that includes daily reporting on new discoveries as they happen and in-depth features that unpack complex debates like this one.
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long after the headlines fade. To get a specially discounted Newcientist digital subscription, head to newcientist.com/youtube.
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And if you're drawn to the kind of scientific discoveries that spark real debate and controversy, then you're going to love the next part.
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Chapter 3, the ancient genetic upgrades. When homo sapiens first ventured across the planet, they encountered new challenges for which in many cases they were dangerously defenseless. Our ancestors faced long odds. Luckily, they also encountered groups of ancient humans who had arrived long before them
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and had through evolution developed natural resistance to the local parasites, pathogens, and other pitfalls. If you were going to invent a part of our genome where it was good to get DNA from somebody really different, the immune system is it because anything
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new can be advantageous against the disease that everybody gets. Getting Neanderl DNA helped our immune systems and the same must have happened over in the far east with genis DNA because of course having evolved in Africa we had
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no natural immunities to the diseases the pathogens the parasites outside of Africa whereas Neandertos and longi had evolved these these over a long time would have evolved resist natural resistances to some of those diseases and pathogens by mating with both Neanderthalss and
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denisans which we now also refer to as homolongi Early homo sapiens got a quick fix to their immune system, the ancient equivalent of a modern technological security patch and thereby acquired traits necessary to flourish throughout Eurasia. These biological shortcuts
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sometimes took on a regional flavor and provided adaptations to local extremes. So Neander diverged east west across Eurasia but the Denisans seem to have been capable of living in very cold conditions in high altitude conditions and also down in the south of Asia and
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island Southeast Asia in tropical and subtropical conditions. Modern Tibetans are famed for their ability to survive and thrive at altitudes where most others tap out.
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About 80% carry a variant of the gene inherited from Denisven. The most famous of these is a Denisven gene that is involved in red blood cell metabolism and enables people who carry the Denisven version of this to have a
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better response to hypoxia. It acts as a biological regulator keeping their blood oxygen efficient in the thin mountain air without the heart straining side effects experienced by everybody else.
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There are other examples of very handy DNA which we inherited off other species. So some Arctic populations carry Denisven genes, Denisven variants of TBX-15 and W2, which acts as an environmental hack.
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While shivering is an adaptation that helps us keep warm, those variants help humans generate heat directly from body fat, a survival trait that may have helped homo sapiens to conquer the north without waiting thousands of years for their own mutations to catch up.
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Borrowed genes, which is what we're talking about, did more than just bolster areas of weakness. In some cases, they also bestowed new strengths.
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People have subjected to measurements and have gone into MRI machines and had their brain scanned and have done, you know, all the blood tests and everything. So, we can say, "Oh, yeah, this Neanderl gene, the people that carry it, it makes this difference."
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Some things we can say unambiguously make a difference. One chunk of Neanderthal DNA carried by some people comes in a variant of the PGR gene which plays a role in pregnancy. And there is some evidence it brings benefits for carriers because it
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appears to promote fertility and reduces the chance of miscarriage. Without DNA like this that we got from Neanderthalss, perhaps our spread across the globe might have stalled. But we weren't just a rising power gobbling up secrets from lesser competitors. The
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reality is far less linear and far more interesting. Chapter 4. The Disan surprise. Human evolution wasn't a tree. As our friend Chris Stringer has described it, it's a braided stream. Imagine a river delta riddled with channels that alternately diverge, meander, and
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converge over and over and over. It won't be a necessarily a simple story because of this more complex web of populations that eventually converged if you like to make what we call homo sapiens today.
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The ancient DNA still living inside us portrays this long and winding backstory. The ultimate example to date was uncovered beginning in 2021 by Fernando Vienna. The story begins in South America and it centers on mucus.
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Not very glamorous yet something that is critical to human survival. Vienna observed that indigenous Americans carry high levels of denisan DNA in the MUC19 gene which affects the consistency of salivory mucus and it was sandwiched between two segments of Neanderthal DNA.
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How did this genetic sandwich get there and what does it tell us? The coolest example is a gene called mucin 19. This gene is one where there was a Denisven variant of this that was brought up into Neanderl populations.
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And we know this because today there's people that carry it. And the people who carry it have a central part of the gene that that is identical to Denise sequences, but around it are two sort of flanking regions that are basically
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identical to Neanderl gene regions. When homo sapiens first arrived in the Americas, likely over 20,000 years ago, they came armed with this mu19 variant.
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It sounds like a minor detail, but in a new and frozen wilderness, this was a matter of life and death, early homo sapiens were adapted to resist pathogens in equatorial Africa. But MUC19 transformed their saliva into a highly
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effective trap that caught pathogens in the Americas before they could take hold. Long before our ancestors set foot in the Americas, Neanderthalss and Denisvens were interbreeding in Eurasia.
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It was there that this Denisven code was stitched into a Neanderthal chromosome. When our ancestors met those Neanderthalss, they inherited the entire genetic sandwich in one piece. We carried that new and improved first line of defense into the Americas, surviving
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a frozen frontier thanks to someone else's saliva. This is a smoking gun. If we had mated with a denisven directly, we would only see the Denisven variant. But because that material is physically stitched inside Neanderthal DNA segments, it
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proves the code was living inside Neanderthalss long before it ever reached a homo sapien. We are the beneficiaries of biological inheritance from our ancient human relatives. And the DNA they gave us has in some cases served us well. But there is a catch.
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Some traits that enabled our survival 50,000 years ago have now in a modern world which is vastly different from the Paleolithic transformed into a curse.
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Chapter 5. The hidden cost of ancient DNA. Take the PGR gene. There is evidence that many people carry a version of this gene that came from the Neanderthalss and it may have boosted the survival of our species by imparting fertility
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benefits as we've mentioned. However, the human body is complicated and a single gene can influence seemingly unrelated processes. In this case, the version of the PGR gene containing Neanderthal DNA has also been linked to a higher occurrence of ovarian cancer.
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So, it's hard to say whether it's beneficial or detrimental. What's clear is that some inherited genetics can both save lives and also on occasion turn against the bodies it was built to protect, particularly when it comes to our immune system. So, it's hard to say
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whether it's beneficial or detrimental. What's clear is that some inherited genetics can both save lives and also on occasion turn against the bodies it was built to protect. By interbreeding with them, we got a quick fix to our immune
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systems. And that was good news 40 or 50,000 years ago. Not such good news today when some of that is linked with autoimmune diseases.
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The Neanthal versions of the IRF5 and stat 4 genes which once stood against lethal infections are now risk factors for the autoimmune disease lupus. The ancient Neanderthal versions of a group of genes called TLR represent yet another evolutionary compromise. TLR
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once helped Eurasian humans ward off parasites, but now may cause immune systems to overreact.
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Basically, allergies. Although that's usually more an annoyance than a matter of life and death, it still shows how DNA from ancient humans can impact lives in the modern world. The effects of our genetic legacy play out in countless and
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often surprising ways. Neanderthal DNA is linked to a higher risk of type 2 diabetes, heart attacks, and even depression. It's also edged into our physical features, the shade of your skin, how easily you tan or burn, and the presence of freckles or red hair.
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Now, I will say a lot of this research is really at the beginning stages. So, sometimes we're seeing associations, but that doesn't necessarily mean that they're definitely linked. And it's also worth saying that perhaps when we first picked up those variants from the
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Neanderthalss and the Discipants and others, the negatives that we experienced from them were less negative because the world of the Paleolithic was so different. Today, many of us live in a world of plenty. Type 2 diabetes as a
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result is more prevalent. However, back in the Paleolithic when food was much more scarce, you can see how potentially type two diabetes would present itself much less. So, if you do have one of these conditions or you just have
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freckles and red hair, don't immediately blame Neanderthalss and denisins. However, the research is plentiful. So, even the shape of your face tells a story. According to a 2023 study, the prominent bridge of your nose, perhaps inherited from Neanderthalss, may be a
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50,000-year-old space heater, a clever device for warming freezing air when the climate was much colder. The legacy of these ancient encounters isn't just hidden in our genes. Every day, it stares right back at us in the mirror.
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Chapter 6. The real story of human origins. By the beginning of the 21st century, the reigning paradigm was the out of Africa model. The idea that modern humans evolved abruptly and conquered the world, completely replacing any and all archaic humans they encountered. But
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over the past 15 years or so, genetics has revealed a much messier truth about our family tree. Our story and the story of the ancient humans in our evolutionary tree is one of continuous shuffling and reshuffleling of a genetic
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deck of cards that has spanned nearly a million years. So what we see from this whole fossil record and indeed the genetic record is that human evolution is a process of diversification.
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And we've got these branching patterns of species diverging from each other. But it wasn't a complete separation because these branches now and again in some places came together and exchanged DNA.
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In 2018, archaeologists found tiny bone fragments of a girl who lived 90,000 years ago whose DNA once sequenced was revealed to be half Neanderthal and half Denisan. She was nicknamed Denny and she represents a miracle find, a first
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generation hybrid. To understand why this is a bombshell, consider the odds. We have only managed to sequence the genomes of a tiny handful of archaic individuals. Statistically, you would think that there is little chance of finding a direct 50/50 hybrid in such a
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small sample. That is unless interbreeding was a common occurrence. The fact that Denny exists in our fossil record might just be a hint that people just like her were a lot more common than we thought. This suggests that when
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different groups of humans met, they didn't necessarily see each other as aliens or different species, they recognized something familiar in each other and maybe even recognized potential partners. Further proof is hidden in Denny's father. Even though he was denisan, his DNA showed he also had
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Neanderthal ancestry further back in his family tree. These groups didn't share just fleeting encounters. They shared a long and fruitful history.
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Those populations that moved eastwards also then met denisans and the denisan interbreeding was added on top of the neanderal interbreeding. Does this have any implication for our understanding of our species? Well, it really depends who you ask. There are plenty of scientists
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who think we can view our ancient human relatives like the Neanderthalss and the Denisven as separate species. But there are also some who think that all of the interbreeding we are now uncovering is evidence that we should see them as
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simply populations within Homo sapiens. that the Neanderthalss and the Denisans actually belong to our species.
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Whichever view you prefer, and both are considered valid right now, there's one inescapable conclusion. Neanderthalss and Denisans and the other ancient humans that lived on our planet over the past 300,000 years never fully lost the ability or the willingness to mingle and
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breed with each other. Maybe not all of them were open-minded enough to consider those liaison, but enough of them were to influence the DNA of people alive today. Until now, we've regarded ancient human species as bit players who
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dutifully vanished once the real protagonists arrived, as evolutionary deadends almost. We've used the word extinct to conjure images of prototypes who came up short, as a synonym for failed. But at our most basic level, our genetic code h that story does
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disintegrate. The Neanderthalss, the Denisans, those ghost species and others whose remains we have yet to reunite with, they did not disappear. Perhaps they were subsumed into a larger human project. They provided the biological armor that allowed us to conquer the
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planet. I think that for us to tell stories and understand the past, we have to think through the diversity of the way that we look at the present. But there's going to be much more to this story, right? It doesn't get simpler. It
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just gets more complicated. In return, their legacy lives on in the shape of your face, the strength of your immune system, and the very blueprint of your survival. They didn't make way for us. They made us. They became us. If you
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want to learn more about who they were, check out our deep dive on the Deniscipans. For years, they were known from nothing more than a tiny fingerbone. Now, scientists think they may have finally found their face, and the discovery could change our entire
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family tree.
Topics:Homo sapienshuman evolutionNeanderthalsDenisovansancient DNAgeneticsinterbreedingghost populationsSvante PääboOut of Africa model
