Christopher: Genetically speaking, you likely have more in common with a stranger from another continent than you do with the person you call your 'race.' That’s not a political statement. It’s a fact, written in the 3 billion letters of your DNA. Lucas: Whoa. Okay, that’s a heavy way to start. It feels like one of those things that should be obvious, but absolutely isn't. It messes with your whole worldview. Christopher: It completely does. And that mind-bending reality is the central theme of the book we're diving into today: 'A Brief History of Everyone Who Ever Lived' by Adam Rutherford. Lucas: Right, and Rutherford isn't just a writer. He's a geneticist with a PhD from UCL and a BBC science broadcaster. What I find fascinating is that he's of mixed heritage himself and has made it a mission to use genetics to dismantle pseudoscience, especially around race. Christopher: Exactly. The book was a finalist for the National Book Critics Circle Award for a reason. It uses our own DNA as a historical document to tell a new story of us. And that story begins in a very, very messy past.

Christopher: So, Lucas, what percentage of your DNA do you think is Neanderthal? Lucas: Hold on, that’s a trick question, right? I thought they were a completely different species that died out. Like, zero percent? Unless my terrible morning mood counts as a Neanderthal trait. Christopher: (Laughs) Well, for a long time, that’s what everyone thought. The story of how we found out the truth is one of the greatest scientific detective stories of our time. It centers on a Swedish geneticist named Svante Pääbo, who took on a seemingly impossible task: sequencing the entire genome of a Neanderthal from a 40,000-year-old bone. Lucas: How is that even possible? Isn't DNA incredibly fragile? I picture it turning to dust after a few hundred years, let alone forty thousand. Christopher: It is. It's a monumental challenge. The DNA is shattered into tiny fragments, and it's massively contaminated with the DNA of bacteria and fungi that have lived on the bone for millennia. Pääbo and his team had to develop entirely new, ultra-clean methods just to isolate the real Neanderthal DNA from all that noise. It took them years. Lucas: Okay, so they're in this hyper-sterile lab, piecing together this ancient genetic puzzle. What did they find? Christopher: They found the smoking gun. They compared the finished Neanderthal genome to the genomes of modern humans from different parts of the world. And the result was shocking: every person today living outside of Africa has between one and three percent Neanderthal DNA in their genome. Lucas: Every person? So you, me, pretty much everyone listening who doesn't have exclusively recent African ancestry… we all have a little bit of Neanderthal in us? Christopher: We do. The evidence points to a period, probably around 50,000 to 60,000 years ago in the Middle East, where our Homo sapiens ancestors met Neanderthals. And as the book humorously puts it, humans are both "horny and mobile." They didn't just fight or compete; they interbred. And those encounters left a permanent echo in our DNA. Lucas: That's incredible. So it wasn't a clean replacement of one species by another. It was a merger, of sorts. Does that Neanderthal DNA do anything? Does it affect our health or appearance? Christopher: It does, in subtle ways. Some of those genes are linked to our immune system, helping our ancestors fight off new pathogens as they moved into Europe and Asia. Others are linked to things like hair and skin characteristics. But it's not all good news; some Neanderthal variants are associated with a slightly increased risk for things like type 2 diabetes or Crohn's disease. Evolution is a trade-off. Lucas: Wow. Okay, so we have these ancient echoes from Neanderthals. But were there other… ghosts in the machine? Other ancient relatives we met along the way? Christopher: I love that you called them ghosts. Because that’s exactly what they are. In 2010, the same lab that sequenced the Neanderthal genome got a tiny fragment of a finger bone from a cave in Siberia called Denisova. It was from a young girl who lived around 41,000 years ago. They didn't even know what species it was. Lucas: Just from a fingertip? What could they possibly learn from that? Christopher: Everything. They sequenced its DNA, and it was neither modern human nor Neanderthal. It was a completely new, third type of human. They named them the Denisovans. We know almost nothing about what they looked like from the fossil record—all we have is that fingertip, a few teeth, and a jawbone. They are a species known almost entirely through their genome. Lucas: A ghost population. That gives me chills. Did we… you know… also get friendly with the Denisovans? Christopher: We absolutely did. And this is where it gets even more complex. People in East Asia have a tiny amount of Denisovan DNA. But populations in Melanesia—people from places like Papua New Guinea and Australia—have up to 6% Denisovan DNA. This means there wasn't just one interbreeding event, but multiple, with different groups, all across Asia. Our family tree isn't a tree at all; it's a tangled, web-like river delta.

Lucas: Okay, so our deep history is a web, not a line. That makes sense for tens of thousands of years ago. But does that same messiness apply to more recent history, like, say, the last 10,000 years in Europe? I feel like we have a clearer picture there from history books. Christopher: That's what we thought. We had stories of Celts, Romans, Angles, Saxons, Vikings—all marching across the land. But genetics has completely upended those neat narratives. For a long time, we assumed the first modern humans to populate Europe after the Ice Age were, well, white. Lucas: Right, you picture ancient Europeans looking… European. Christopher: Prepare to have your mind blown. In 2014, scientists sequenced the DNA of an 8,000-year-old skeleton found in Luxembourg. They called him "Loschbour Man." He was a hunter-gatherer, one of the first people to resettle Europe. And his genes showed, unequivocally, that he had dark, likely black, skin and striking blue eyes. Lucas: Wait, what? Dark skin and blue eyes? That’s a combination you almost never see today. So the original Europeans weren't white? Christopher: Not as we think of it. The genes for pale skin only became common in Europe much, much later. Loschbour Man represents the first of three major waves of migration that formed modern Europeans. He was from the first wave: the indigenous hunter-gatherers. Lucas: Okay, so what were the other two waves? Christopher: The second wave happened around 7,500 years ago. Farmers from the Near East—Anatolia, modern-day Turkey—began moving into Europe, bringing agriculture with them. They brought new genes, a new diet, and a new way of life. They mixed with the local hunter-gatherers, and the genetic landscape of Europe began to change. Lucas: And the third wave? Christopher: This one is the most dramatic. Around 5,000 years ago, a new group swept in from the Russian and Ukrainian steppes. They were called the Yamnaya. They were pastoralists, they rode horses, they had wheeled carts, and they seem to have had a massive impact. In some parts of Europe, like Britain, they replaced up to 90% of the existing gene pool within a few hundred years. Lucas: Ninety percent? That’s not a migration; that's a takeover. So modern Europeans are a blend of these three ancient populations: dark-skinned hunter-gatherers, Near Eastern farmers, and steppe horse-riders? Christopher: Precisely. We are all mongrels, a mix of these three ancestral streams. And this completely dismantles the idea of any 'pure' European nationality. Take the British Isles. A massive project called the 'People of the British Isles' project analyzed the DNA of thousands of people whose four grandparents were all born in the same small area. Lucas: What did it find? Is there a 'Celtic' gene or an 'Anglo-Saxon' gene? Christopher: Not at all. It found that the so-called 'Celts' in Scotland and Wales are genetically quite different from each other. In fact, the Welsh are more different from the Scottish than either group is from the English. The idea of a single, unified Celtic people is a cultural and linguistic myth, not a genetic reality. The Anglo-Saxons didn't wipe out the native Britons; they integrated with them. And the Vikings, despite their fearsome reputation, left a surprisingly small genetic footprint outside of a few specific areas. Lucas: So all that stuff about pure-blooded Vikings or ancient Celtic bloodlines is just… romantic nonsense? Christopher: It's beautiful, powerful nonsense. But from a genetic standpoint, yes. The history written in our genes is one of constant movement, mixing, and replacement.

Christopher: And this idea of 'pure' peoples brings us to the most explosive topic in the book, and the one Rutherford handles with incredible care: the concept of race. Lucas: This is the big one. Because on one hand, you're telling me we're all mixed and interconnected. But on the other hand, I can walk outside and see clear physical differences between people from different continents. How does genetics square that circle? Christopher: It squares it by showing that our eyes are deceiving us. The physical traits we use to define race—skin color, hair texture, eye shape—are controlled by a tiny, tiny fraction of our 20,000 genes. They are superficial adaptations to local environments, mostly climate. Lucas: So they're just on the surface? Like the cover of a book doesn't tell you what's inside? Christopher: Exactly. And the data to prove this is overwhelming. In 1972, a Harvard geneticist named Richard Lewontin did a landmark study. He looked at genetic variation in populations across the world. He expected to find big, clear genetic divisions between Caucasians, Africans, Asians, and so on. Lucas: And he didn't? Christopher: He found the exact opposite. He discovered that a staggering 85% of all human genetic variation exists within any local population. For example, within the population of Kenya. Only about 6-7% of variation actually accounts for the differences between so-called races. Lucas: Hold on, let me see if I get this. You could take two random people from a village in Nigeria, and the genetic difference between them is likely to be far greater than the average difference between that village and a village in, say, Sweden? Christopher: That is precisely what the data shows. Biology fundamentally deceives our eyes. We see skin color because it's obvious, but we don't see the vast, complex genetic diversity in immune systems, metabolism, and thousands of other things that don't align with those superficial racial categories. As Rutherford puts it, as far as genetics is concerned, race does not exist. Lucas: Okay, but then what about those DNA ancestry tests? The ones that tell you you're 40% Irish, 20% Scandinavian, and 10% Nigerian. Are those just fake? Christopher: Rutherford calls them "genetic astrology," which I think is perfect. They aren't entirely fake, but they are deeply misleading. They compare your DNA to a reference database of modern people from certain areas and find statistical correlations. But they present these probabilistic matches as concrete ancestral identities. They can't tell you that your great-great-great-grandfather was a Viking. They can only tell you that a piece of your DNA is commonly found in people living in Scandinavia today. It's a subtle but hugely important difference. Lucas: So it's playing on our desire for a simple story, a neat identity, when the reality is that messy, tangled web we talked about. Christopher: Exactly. The book gives a great example with the EDAR gene. A single mutation in this gene, which arose in China about 30,000 years ago, is responsible for a suite of traits common in East Asians: thicker hair, more sweat glands, and a particular tooth shape. It's a powerful gene that creates a distinct look. But does that one gene create a separate 'race'? Of course not. It's just one tiny variation in a genome of 3 billion letters.

Lucas: Wow. So if our deep past is a tangled web, our recent history is a story of constant mixing, and race isn't biologically real... what's the big takeaway? What is the story our genes are really telling us? Christopher: The story is one of profound and beautiful interconnectedness. Our DNA is a testament to migration, mixing, and adaptation. It proves we are one, incredibly diverse, human family. The divisions we create—race, nationality—are social and political inventions, not biological realities. They are powerful, and they have real-world consequences, like racism. But they are not written into our code. Lucas: So the science itself is a unifying force. Christopher: It is. And as Rutherford points out, there's a beautiful irony here. The science of genetics, which was born in the late 19th and early 20th centuries, was immediately co-opted by eugenicists and racists to try and prove their hierarchies, to divide us. But now, a century later, that very same science has become the most powerful tool we have for proving our fundamental unity. Lucas: That's a powerful thought. It makes you look at a crowded train or a city street completely differently. You're not just seeing a collection of strangers; you're seeing thousands of individual, 4-billion-year-long stories that all, eventually, connect back to the same chapter. Everyone is a living library of human history. Christopher: Exactly. And that's a history that belongs to all of us. We'd love to hear how this changes your perspective. Drop a comment on our socials and let us know what you think. Does knowing this change how you see yourself or the world? Lucas: It's a lot to chew on. A brilliant, humbling, and ultimately hopeful story. This is Aibrary, signing off.