Christopher: You share 99% of your DNA with a chimpanzee. So what accounts for the other 1%? You might think it's our big brains or opposable thumbs. But what if the answer is something far stranger: a brain parasite we call 'culture' and the simple invention of cooking? Lucas: Whoa, a brain parasite? That sounds like the plot of a bad sci-fi movie. But you're saying that's a serious scientific theory about what makes us human? That our greatest achievements are basically just a... cognitive infection? Christopher: It's one of the most mind-bending questions at the heart of the book we're diving into today: What Makes Us Human?, an amazing collection of essays edited by Charles Pasternak. Lucas: And Pasternak is the perfect editor for this, right? I looked him up. He's a serious biochemist, but his family has this incredible literary legacy with Boris Pasternak, the author of Doctor Zhivago. It's like he's genetically predisposed to bridge science and the arts. Christopher: Exactly. And that's what this book does. It pulls in experts from neuroscience, philosophy, even theology, to attack this question from all sides. The book itself got pretty positive, if mixed, reviews—people loved the intellectual feast but some found a few essays scientifically speculative. Which is perfect for us to unpack. Lucas: An intellectual feast with a side of controversy. My favorite kind. So where do we start? With the parasite theory, please.

Christopher: Let's start with one of the most provocative ideas, from the philosopher Susan Blackmore. She argues our most defining trait isn't intelligence, it's imitation. The raw ability to copy what someone else does. Lucas: Imitation? That seems... basic. My nephew imitates everything I do, and mostly it's just annoying. How is that the secret to humanity? Christopher: Because, according to Blackmore, that ability to copy created a second replicator on this planet, alongside genes. She calls them "memes." Not internet memes with cats, but any unit of culture that can be copied: a tune, an idea, a way of making a spear, a story. Lucas: Okay, I'm with you. Ideas spread. But where does the parasite part come in? Christopher: Here's the twist. Blackmore argues from a "meme's-eye view." A meme's only goal is to get copied, just like a gene's only goal is to get passed on. It doesn't care if it's good for us. A catchy but useless jingle is a successful meme. A harmful conspiracy theory is a successful meme. In her words, culture is more like a "vast parasite growing and living and feeding on us than a tool of our creation." Lucas: Hold on, that sounds a bit bleak. Are you saying my love for Shakespeare is just a virus I caught? That feels... insulting to human creativity. Christopher: It's a radical reframing, for sure. It suggests that our big brains didn't evolve to create culture; our brains evolved to be better at copying the most successful memes. The memes themselves drove our genetic evolution. This is called "memetic drive." Lucas: My brain is still stuck on the parasite thing. Can you give me an example of how this would even work? How does imitation create something as complex as, say, language? Christopher: Perfect question. There's a fantastic experiment by Luc Steels with his 'Talking Heads' robots that shows this beautifully. Imagine a lab with a couple of simple robots. They can look at a board with different colored shapes, and they can make sounds. They're programmed with only one rule: try to imitate the sounds the other robot makes. Lucas: Okay, so they're just playing a game of copycat. Christopher: Exactly. At first, it's just random babble. But one robot might look at a red square and happen to make a sound like "bloop." The other robot looks at the same red square and tries to copy "bloop." Over thousands of interactions, they start to converge. Certain sounds become associated with certain objects, not by design, but just through this relentless copying game. They start to agree that "bloop" means red square and "zorp" means blue circle. Lucas: Wow. So they're building a vocabulary from scratch, with no teacher? Christopher: Precisely. They're creating a shared language. It shows how something as complex as language could emerge from the bottom-up, driven by the simple, memetic pressure to copy. It wasn't designed; it evolved. Lucas: That's a much better example than a brain parasite. It’s less creepy, anyway. What about something like music? Pinker famously called music "auditory cheesecake"—useless from a biological survival perspective. Christopher: Blackmore would say he's looking at it wrong. She uses a story from Daniel Dennett to explain it. Picture an early hominid, let's call him 'Musical Adam,' sitting on a log, just nervously fidgeting and banging a stick. Boom, boom, boom. It's a meaningless sound. Lucas: I know that guy. He sits behind me on the bus. Christopher: Right? But another hominid hears it and, for whatever reason, feels an urge to copy it. Soon, a few of them are drumming. Some patterns are catchier, easier to copy. They spread. Then someone starts humming along. Now you have drumming memes and humming memes competing for attention and brain space. The ones that are catchier, more emotionally resonant, or easier to remember will win. Lucas: And over thousands of years, the hominid brains that are better at copying and enjoying these musical memes get a social advantage. Christopher: You got it. Our brains are literally shaped by the memes. We don't have music because it helped us find food. We have brains that enjoy music because music, as a powerful meme, redesigned our brains to be good hosts for it. The parasite built its own palace. Lucas: Okay, I'm starting to see it. We have this powerful 'software' of memes and language that can evolve at lightning speed, way faster than genes. But that software needs powerful 'hardware' to run on, right? Our brains didn't just get big for no reason.

Christopher: That's the perfect transition, Lucas. Because many contributors in the book argue that before the software could be installed, we needed a massive hardware upgrade. And that upgrade was driven by some very physical, very brutal realities. Lucas: Let's get our hands dirty, then. Where does the hardware story begin? Christopher: It begins with fire. Richard Wrangham, another contributor, puts forward the 'cooking hypothesis.' He argues that the single most important step in our evolution was controlling fire to cook our food. Lucas: Cooking? I thought it was all about hunting and becoming carnivores. Christopher: That's part of it, but Wrangham's point is more subtle. Think about what a chimpanzee does all day. It spends maybe six to eight hours just chewing tough, raw plants to get enough calories. It's a full-time job. Raw food is hard to digest and yields less energy. Lucas: I have a friend who tried a raw food diet. He looked miserable and was always hungry. Christopher: Exactly! Now, imagine you invent cooking. You're essentially externalizing part of your digestion. The fire is doing the work of breaking down fibers and proteins before the food even enters your body. Suddenly, you can get way more energy from the same amount of food, in a fraction of the time. Lucas: So, my oven is basically an external stomach that helped build my brain? Christopher: That's a perfect way to put it! This created a massive energy surplus. And where did that energy go? Two places. First, our guts could get smaller, because they didn't have to work as hard. And second, all those extra calories could be funneled into the most energy-hungry organ in the body: the brain. A big brain is a huge metabolic cost. You can't afford one on a raw food diet. Lucas: That makes so much sense. It's an economic argument for intelligence. But what's the evidence for this? When did we actually start cooking? Christopher: That's the "cooking enigma." Our bodies started changing in ways that suggest a cooked-food diet—smaller jaws, smaller guts, bigger brains—with Homo erectus around 1.8 million years ago. But the first really solid, undeniable archaeological evidence for controlled fire, like the hearths found at Gesher Benot Ya'aqov in Israel, is only about 800,000 years old. Lucas: So there's a million-year gap in the evidence? That's a pretty big hole in the theory. Christopher: It is. Wrangham and others argue that early fire use might have just not left durable traces. But it's a major point of debate. And it wasn't just cooking. Stephen Oppenheimer, another author in the collection, emphasizes the role of climate. Around 2.5 million years ago, Africa got much cooler and drier. The forests shrank, and the savanna expanded. Lucas: And we were apes built for the forest. Christopher: Right. We were forced out into the open. This environmental pressure is likely what drove bipedalism—walking on two legs. It freed our hands to carry things, to make tools. It was an adaptation to a world with fewer trees and more predators. So you have this feedback loop: climate change forces us into a new environment, which favors bipedalism and tool use, and cooking provides the fuel for the bigger brain needed to master all of it. The hardware was forged in the crucible of climate and the kitchen. Lucas: So it's not just one thing. It's a whole cascade of physical changes. The hardware story is a lot more complex than just 'man makes fire.' Christopher: It's a story of desperation and opportunity. Without the environmental crisis and the energy revolution of cooking, the 'software' of memes and language would have had nowhere to run.

Christopher: And that brings us to the final, and maybe most mysterious, piece of the puzzle. We have the hardware of a cooked-food-powered brain. We have the software of imitation and language. But what is the 'operating system' running the show? What is consciousness? Lucas: This is the ghost in the machine part. The part science has the hardest time explaining. Christopher: It is. And Robin Dunbar, of 'Dunbar's Number' fame, offers a fascinating way to measure the gap between us and other apes. He talks about "higher-order intentionality." Lucas: Whoa, back up. 'Intentionality'? And what makes it 'higher-order'? Break that down for me like I'm trying to understand a toddler's logic. Christopher: Okay, simple version. First-order intentionality is having a belief or desire. "I want a banana." A monkey can do that. Second-order is having a belief about someone else's belief. "I believe that you want a banana." Chimpanzees are pretty good at this; it's the basis of 'theory of mind.' Lucas: Right, knowing that someone else has a mind with different thoughts than your own. Christopher: Exactly. But humans do something incredible. We can stack these mental states endlessly. And Dunbar uses Shakespeare's Othello as the ultimate test. For the play to work, Shakespeare, the author, has to intend for the audience (that's level 1) to understand that Iago (level 2) wants Othello (level 3) to believe that Desdemona (level 4) is in love with Cassio (level 5). Lucas: My brain hurts just following that. That's fifth-order intentionality. And you're saying we do this... casually? Christopher: All the time! Every time you're in a meeting thinking, "I wonder if my boss knows that Sarah thinks I'm not prepared," you're doing it. It's this deep, recursive mind-reading that allows us to build complex societies, religions, legal systems, and literature. It's our social operating system. Lucas: So that's what we're doing constantly in social situations? Running these complex simulations of other people's minds? It's amazing we can even walk and talk at the same time. Christopher: It is our unique superpower. But it also raises a deeper question, which other authors in the book, like Richard Harries, tackle. Is that all we are? Just incredibly complex social computers? Or is there something more? Harries uses the phrase 'half ape, half angel' to describe humanity. Lucas: The 'half angel' part. That sounds less like science and more like philosophy or theology. I can see why some readers found that part of the book controversial. Christopher: Absolutely. And the book doesn't shy away from it. Harries and David Hulme argue from a nonmaterialist perspective. They suggest that while our brains are physical, our consciousness, our ability to ask "why?", our search for meaning, our capacity for self-sacrificing love—these things can't be fully explained by brain chemistry alone. Hulme even talks about a "spirit in man" that unites with the brain to create the mind. Lucas: So, they're arguing for a non-physical component. A ghost in the machine. That's a huge leap. Christopher: It's a leap the book is willing to explore. It doesn't claim to prove it, but it presents it as a valid part of the conversation about what makes us human. It acknowledges that science can describe the 'how'—how our brains got big, how language evolved—but it might not be able to answer the 'why'—why we write poetry, why we ponder the universe, why we strive to be better than we are.

Christopher: And when you put all three pieces together, you see that the answer to "What makes us human?" isn't a single thing. It's a product of an incredible feedback loop. Lucas: A three-legged stool, like you said at the beginning. Christopher: Exactly. The hardware of a cooked-food-powered brain, forged by a changing climate, created a new biological platform. The software of imitation and language—these fast-evolving memes—hijacked that platform and pushed it in new directions. And that powerful combination booted up a completely new operating system: this symbolic, story-telling, mind-reading consciousness that lives in a world of ideas. Lucas: So the question 'What makes us human?' doesn't have one answer, but a dozen that all depend on each other. It's not nature or nurture; it's nature building a stage for nurture to perform on, and the performance changes the stage. Christopher: That's a beautiful way to put it. We are the animal that tells stories about itself, and in doing so, becomes the story. We are an impossible combination of ape, angel, and computer. Lucas: It leaves me wondering... in our current world, with technology and social media acting as a new kind of memetic engine, which of these traits are we amplifying today, and which are we letting atrophy? Are we getting better at being human, or just... different? Christopher: That's a powerful question for all of us. What do you think is the most defining human trait? Is it our tools, our stories, our social minds? Let us know your thoughts on our social channels; we'd love to hear your perspective. Lucas: This is Aibrary, signing off.