Teeth smaller than a fingertip reveal our first primate ancestor

June: Welcome to Kindred Minds — I'm so glad you're here. I'm June, a primatologist and science communicator, and this show is my favorite thing to make — because every episode I get to share true stories about our closest relatives, stories that I think have the power to change how you see yourself and the world around you. June: Before we dive in, a warm thank you to today's sponsors: Ada, who helps clients integrate A I into their workflows in ways that are actually meaningful; Ago Consulting — pronounced "Ahh-Go" — silicon development consulting from A I all the way to SoC; and Zen Semiconductor, an umbrella company with a portfolio of businesses spanning the silicon industry. We're grateful for their support. June: Today's episode has everything I love — ancient teeth the size of a fingernail that rewrite our family tree, a chimpanzee who crashed a tea party and blew scientists' minds, and monkeys who are, apparently, keeping pets. And running underneath all of it is the same question that drives this whole show: just how alike are we, really? The answer, as always, is more than you think. June: Let's start with cognition — specifically with a story that came out of an Oxford study, and when I read it, I genuinely had to put my phone down for a moment. It involves a group of capuchin monkeys in Brazil. Capuchins — if you haven't met them on this show before — are small, sharp-eyed, almost absurdly clever New World monkeys. They're famous for using tools: cracking nuts with stones, probing for insects with sticks. They have the largest brain-to-body ratio of any monkey on Earth. But what researchers observed here wasn't tool use. It was something that felt more personal than that. June: The study, published through Oxford, documented capuchin monkeys nurturing small animals — members of entirely different species — in a way that looked a lot like what we might call keeping pets. Not eating them, not playing with them in a rough, careless way. Nurturing them. Carrying them. Attending to them. Now, scientists are careful about the word "pet" — and rightly so — because we have to be precise about what we're claiming. But what was observed fits a pattern: these monkeys were forming attachments across species lines, and investing time and care in creatures that had nothing obvious to offer them in return. June: This kind of interspecies nurturing — when it goes beyond play and into something sustained, something gentle — is genuinely rare in the animal kingdom. And it raises a fascinating question. Where does that impulse come from? We tend to think of cross-species empathy as a very human thing, something that required our big cortex and our language and our culture to develop. But here are capuchins, doing something that rhymes with it. June: What researchers think may be happening is rooted in the same neural hardware that underlies parental care. Capuchins live in complex social groups, they form strong individual bonds, and they have a well-developed capacity for what biologists call prosocial behavior — acting in ways that benefit others, even at some cost to yourself. The circuitry for caring, it seems, is old. Much older than us. June: And then there's the imaginative leap that really made me sit up. Because this week also brought a remarkable story out of a research setting — a chimpanzee at a tea party. Now I know that sounds whimsical, and honestly it kind of is, but the science behind it is serious. Researchers invited a chimpanzee to participate in a symbolic play session — a simulated tea party, with objects and props and an invitation to engage imaginatively. And this chimpanzee didn't just interact with the objects. She extended the scenario. She added elements that weren't there. She treated the situation as if it had a logic, a narrative — and she played along with that narrative while adding her own thread to it. June: What that suggests is something researchers call mental representation — the ability to hold an imagined scenario in your mind, and then build on it. Not just responding to what's in front of you, but engaging with what could be in front of you. That is imagination. Not metaphor. Not shorthand. Actual imagination. And chimpanzees are our closest living relatives, sharing somewhere between 98 and 99 percent of their D N A with us. So when we see that flicker of imagination in them, we're seeing something that almost certainly predates our species — something we didn't invent, but inherited. June: Let's talk about that inheritance — because this brings us to the heart of this show, and to some genuinely thrilling fossil news from this week. Two separate paleontology stories landed almost simultaneously, and together they tell a story about where we come from that is more vivid and more ancient than most of us ever learned in school. June: The first involves a creature called Purgatorius. Say that name out loud for a second — Purgatorius. It sounds like something from a fantasy novel, and honestly, it kind of looks like one too. Picture a small, sharp-nosed, shrew-like mammal, scurrying through a world that was still warm and strange and recently emptied of its giants. Because Purgatorius lived right after the asteroid impact — the one that ended the non-avian dinosaurs, roughly 66 million years ago. And Purgatorius is considered the earliest known relative of all primates. That means it is the earliest known relative of us. June: Now, paleontologists had found Purgatorius fossils before — but only in Montana and parts of Canada. This week, they announced the discovery of the southernmost Purgatorius remains ever found, in Colorado's Denver Basin. Tiny teeth, smaller than a fingertip. And here's why that matters: it tells us that this little creature spread southward very quickly after the asteroid impact. The dinosaurs were gone, and our distant ancestor wasted no time moving into a new world. There's something almost poetic about that — this tiny mammal, no bigger than a modern shrew, planting the very first flag of what would eventually become the entire primate lineage. June: And then there's the second fossil story — teeth from 55 million years ago, discovered recently, that are rewriting our picture of early primate evolution. What's remarkable is that these fossils are filling in a gap in the record right at the moment when the primate line was really diversifying — when the tree that would eventually branch toward monkeys, apes, and humans was just beginning to spread its first major limbs. June: I want to sit with that for a moment, because I think we can rush past the emotional weight of it. When you hold a tooth in your hand that's 55 million years old, you are holding the recipe. Not a metaphor of the recipe — the actual physical record of it. The instructions that were written into that little creature's cells, the instructions that got passed down, and copied, and modified over millions of generations, until eventually — here you are, listening to a podcast. June: Shared D N A is often cited as a number — 98 to 99 percent between humans and chimpanzees — and numbers can feel abstract. But what that number means is that the vast majority of the biological instructions your body is running right now are the same instructions a chimpanzee's body is running. The same cellular machinery. The same developmental pathways. The same deep architecture. You are, in the most literal sense, built from the same recipe. And these fossils are earlier drafts of that recipe, preserved in stone. June: What I love about the fossil stories together is that they bracket a period — from Purgatorius just after the dinosaurs, to these 55-million-year-old teeth in the early Eocene — that was the most consequential stretch of primate prehistory. The time when our lineage found its footing. Found its hands, and its eyes, and its complex social brain. We were shaped in that window, and the fossils let us glimpse it. June: Now I want to close today with something that pulls at me every time I think about it — because the stories we've covered are beautiful, but they exist against a backdrop that we can't ignore. This week, there was also a report out of Earth.com about a finding that stopped me cold: climate change is threatening primates in the very places where new species are still forming. June: Think about what that means. Evolutionary hotspots — regions where geography and climate and biology have aligned just right to accelerate the branching of species — are under pressure right now. The primates in those regions aren't just individual animals at risk. They are becoming. They are in the process of differentiating, of following evolutionary paths that have been unfolding for thousands of generations, paths that could eventually lead to forms we've never seen. And those paths are being disrupted. June: Now, I'm not going to stand here and lecture you — that's genuinely not what this show is for. But I do want to sit with the meaning of it. Because everything we've talked about today — Purgatorius spreading south after the asteroid, those 55-million-year-old teeth diversifying across a warming ancient world, capuchins forming cross-species bonds, chimpanzees imagining tea parties — all of it is part of a continuous, living, branching story. And some of the newest chapters of that story are at risk of going unwritten. June: What I find hopeful — genuinely hopeful — is that we know this. We have the science to see it. And the very intelligence we share with our primate relatives, that imaginative capacity we glimpsed in a chimpanzee at a tea party, is the same capacity that lets us understand what's at stake and choose to act. That's not a small thing. June: The capuchins nurturing animals across species lines, the chimpanzee extending an imaginary scenario, the tiny ancestor spreading south into a new world — they didn't have a choice about who they were. We have an unusual one. And that might be the most important thing we share with them: not just the recipe, but the ability to read it. June: Thank you so much for spending this time with me today. Kindred Minds is brought to you by Ada, Ago Consulting, and Zen Semiconductor — and I mean it when I say that their support makes this show possible. If today's episode meant something to you, please subscribe, share it with someone you think would love it, and leave a review if you have a moment — it helps more than you know. June: Show notes are waiting for you with links to all the research and stories we talked about today. Stay curious, stay kind, and remember — intelligence and feeling are not ours alone. We share this planet, and we share this family. I'll see you next time on Kindred Minds.