Decoding function in primate facial expressions: re-evaluating broader contexts and terminology - Frontiers

June: Welcome to Kindred Minds. I'm June, a primatologist who has spent her career falling more in love with our primate relatives every single day — and this show is where I get to share that love with you through true stories, real science, and the kinds of moments that make you go, wait, they do that too? Before we dive in, a warm thank you to today's sponsors: Ada, who helps businesses integrate A I into their workflows in ways that actually make sense; Ago Consulting — pronounced "Ahh-Go" — silicon development experts working across everything from A I to full SoC design; and Zen Semiconductor, an umbrella company with a whole portfolio across the silicon industry. We're grateful for their support. Today on the show — we're going to talk about what primate faces are really saying, whether being smart actually helps you survive in the wild, and a bonobo named Kanzi who sat down to an imaginary tea party and absolutely blew scientists' minds. The through-line today, as always: just how alike we truly are. June: So let's start with faces. Human faces. Primate faces. And the science of what those faces are actually doing. Because here's something I think about a lot — when you smile at a stranger and they smile back, something real just happened. Information moved between two animals. And that is not a small thing. Researchers publishing in Frontiers have been doing a deep re-evaluation of how we think about and talk about facial expressions across primates — and their work is nudging the field toward something more honest and more fascinating than the old framework. For a long time, scientists were cautious — almost allergic — to the idea of describing primate facial expressions in emotional terms. You'd say "the chimpanzee produced a silent bared-teeth display" rather than "the chimpanzee smiled." And that caution came from a good place. Science needs rigor. We don't want to just project our feelings onto other animals without evidence. But what this newer research is pointing out is that the old clinical terminology might have actually obscured something real. Because when you look at the breadth of what primate faces do — across dozens of species, in social contexts, in moments of play, of fear, of greeting, of reconciliation — these expressions are not just reflexive muscle twitches. They are functional. They carry meaning. They communicate. Chimpanzees have a play face — this open-mouthed, relaxed expression — that is deeply analogous to our laughter. It shows up in the same contexts: rough-and-tumble play, chasing, tickling. And it's contagious, just like laughter is for us. Macaques use lip-smacking as a friendly, affiliative signal — a way of saying, I am not a threat, I am with you. Gorillas have a suite of subtle facial signals that experienced observers learn to read almost the way you'd read a person's mood across a dinner table. And what this research is urging us to do is think more carefully about the function of these expressions — what they do in the social world of the animal — rather than just cataloguing them as neutral behaviors. Because when you look at function, you start to see something that looks a lot like communication. Intentional, context-sensitive, socially embedded communication. Now, does that mean chimpanzees feel joy the way you feel joy? That's a genuinely hard question and I don't want to oversell it. But the evidence is growing that the machinery of emotional expression — the faces, the vocalizations, the body postures — is not something humans invented. We inherited it. We are one branch on a very old tree, and the faces we make at each other, the way a smile disarms a room, the way a furrowed brow says something without a single word — all of that has deep, deep roots. Roots that go back millions of years, shared with beings who are still here, still making faces at each other in forests and savannas right now. June: And that brings me beautifully into our second thread today — the shared biology that makes all of this possible. Because when we talk about primate facial expressions being functional and communicative, there's an obvious question underneath it: why? Why would evolution produce this kind of elaborate, nuanced, socially rich communication system across so many species? And the answer lives in the D N A. We share somewhere between 98 and 99 percent of our D N A with chimpanzees. With gorillas, it's around 98 percent. Even with more distant relatives — macaques, for example — we still share the vast majority of our genetic code. And what that means in practice is that we are running on the same basic recipe. The same genes that wire up the human social brain are variants of genes found across the primate family. The same neural circuits that let you read a friend's face — that lightning-fast, unconscious process of recognizing threat versus warmth, sadness versus delight — those circuits have analogues in chimpanzee brains, in macaque brains, in the brains of animals who have never met a human but who navigate their own complex social worlds every single day. Now, a new study published in Science brings this into sharp, almost startling focus — because it asks a question that sounds almost philosophical but turns out to be deeply empirical: does being smarter actually help you survive? And in a wild primate population — vervet monkeys — the answer appears to be yes. Researchers tested wild vervets on a series of cognitive tasks: things like figuring out how to extract food from a container, or solving a problem they hadn't encountered before. And then they tracked those same animals over time. What they found is that the individuals who performed better on those cognitive tasks had higher fitness — meaning they survived better, reproduced more successfully. This is actually really significant, because for a long time there was a debate in evolutionary biology: is big-brained, high-cognition primates intelligence actually adaptive — does it genuinely help you live and pass on your genes — or is it a kind of expensive luxury that evolved for other reasons? This study is one of the clearest pieces of evidence yet that cognitive ability, in the wild, under real conditions, translates into real survival advantage. And here's the kicker that connects back to our shared biology. If intelligence is genuinely adaptive in our primate relatives — if the ability to solve novel problems, to remember, to reason, gives you an edge in the real world — then we are looking at the same selective pressure that shaped us. Not a pressure that singled out humans for special treatment, but one that was operating across the primate lineage, tuning up brains, building social intelligence, rewarding flexibility and learning. We didn't arrive at intelligence from nowhere. We rode a wave that was already building for tens of millions of years. June: Okay. Now I want to tell you about Kanzi. And I want you to picture this scene: a bonobo, sitting across from a researcher, and on the table between them — nothing. No juice. No grapes. Nothing. But the researcher says, here, I'm pouring you some juice. And points to an empty cup. And Kanzi — this remarkable bonobo who has been part of decades of language research — plays along. He tracks the imaginary juice. He points to where the pretend grapes were placed. He acts as though these things are real, even though he can see perfectly well that they are not. And when actual, real food is offered alongside the pretend scenario, he picks the real food — which tells you he is not confused. He knows the difference. He is choosing to engage with the fiction. Scientists published findings on this and the word they used — carefully, after a lot of scrutiny — was imagination. The capacity to represent things that aren't there. To hold a mental model of something absent and act on it. This is the cognitive bedrock of so much of what we consider uniquely human. Pretend play. Storytelling. Planning. Empathy — because empathy requires you to imagine someone else's inner world, something you cannot directly see. And here is Kanzi, doing it. Now, Kanzi is not a typical bonobo in the sense that he grew up in an extraordinary research environment and was exposed to human language from a very young age — he communicates using lexigrams, symbols on a keyboard, and has been the subject of research for decades. So we should be careful about generalizing from him to all bonobos everywhere. But what his case does — and what cases like his do — is prove that the capacity exists. The neural architecture for imagination, for pretend, for mentally modeling absent things — it is there. It exists in a bonobo brain. And that should make us ask: if it exists there, where else does it exist? Because bonobos and chimpanzees are our closest living relatives. We share a common ancestor with them that lived only around six million years ago — which in evolutionary time is practically last Tuesday. The cognitive gifts we think of as ours — language, imagination, theory of mind — we didn't conjure them from nothing. We built on a foundation. And Kanzi, sitting at that table with his imaginary tea party, is a living, breathing reminder of what that foundation looks like. Now, I have to pair this story with something that breaks my heart a little, and I think it's important to sit with both feelings at once — the wonder and the grief. Because there's a species of great ape right now that is so rare, so endangered, that every individual life is precious beyond measure. Tapanuli orangutans. They were only formally described as a distinct species in 2017 — and at that point, scientists estimated there were fewer than 800 of them left in the entire world. Eight hundred. That's less than the population of some small towns. They live in a small patch of highland forest in northern Sumatra, in Indonesia. And recently, devastating floods hit that region. And conservationists and researchers are now deeply worried — genuinely fearful — that some of those orangutans, animals with rich cognitive lives, with social bonds, with personalities, with the same capacity for imagination and connection we're celebrating in Kanzi today — may have been swept away. We don't have final numbers yet. The situation is still being assessed. But the fragility of it is almost unbearable to contemplate. These are not abstractions. These are individuals. Known individuals. Animals that researchers have spent years coming to know. And the world would be so much poorer, so much smaller, without them. I think about Kanzi playing his tea party game, holding imaginary things in his mind, and I think about what it would mean to lose an entire species of mind like that. It's not just a conservation statistic. It's a loss of a kind of knowing, a way of being in the world, that took millions of years to build. We are on the same side of this planet. We always have been. June: So here's where I want to leave you today. Faces that communicate across millions of years of shared evolution. Brains that are smarter because being smarter genuinely helps you live. A bonobo who imagines. And a species so rare that a single flood could reshape their future. What today has been, really, is a portrait of kinship. Not a metaphor for kinship — actual, biological, molecular, neural kinship. We share the recipe. We share the architecture. We share so much more than most people ever get told. And I think when we really feel that — when we let it land — it changes something. It changes how we see the forests. It changes how we see the animals in them. It changes how we see ourselves. This has been Kindred Minds, brought to you by Ada, Ago Consulting, and Zen Semiconductor. If today's stories moved you, please subscribe wherever you listen, leave a review if you have a moment, and share the episode with someone who might need a little more wonder in their week. All the research and sources we talked about today are in the link in show notes. Stay curious, friends. And remember — you have never been as alone in the universe as you thought.