Most readers who know the Barbary macaque at all know it as the “ape” of Gibraltar, a population that humans introduced, and perhaps as a species of the Atlas Mountains, where something like 8,000 survive in the forests of Morocco and Algeria, up to 2,300 metres. The mental picture of Middle Pleistocene Germany is a different animal list: aurochs, horse, giant deer, a cold steppe with a few trees. Monkeys do not belong in it. Thijs van Kolfschoten, of the Faculty of Archaeology at Leiden University, who led the study, puts the distance plainly in the accompanying release: Schöningen lies about 1,800 kilometres north of where the species lives today.

The tooth matters beyond the map, because it was found in a layer that also holds evidence of people. Hominins were working flint and burning wood on the same shore, and the authors, who include Jordi Serangeli of the University of Tübingen’s Senckenberg Centre for Human Evolution and Palaeoenvironment, who directs the Schöningen excavations, and Ivo Verheijen of the Lower Saxony State Office for Cultural Heritage, name increased human predation as one possible reason the species later vanished from Europe. They give it as one candidate alongside vegetation change, and they do not claim to be able to separate the two.

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The belief this work disturbs is a comfortable one, and it is held by most readers who have thought about chimpanzees at all: that the animal in front of the tray is a calculator, weighing fruit against retaliation, and that whatever restraint it shows is the residue of fear. The published literature has leaned that way for years. Chimpanzees do not appear to respect ownership in any formal sense; in one 2020 experiment by Patricia Kanngiesser and colleagues, the participant allowed to monopolize a set of food rewards did so in 95% of trials. In an earlier tray-and-rope experiment by Keith Jensen, Josep Call and Michael Tomasello, theft occurred in 74% of trials, and the victims took revenge by collapsing the tray so that neither animal got the food. If chimpanzees steal whenever theft is cheap, then a chimpanzee that doesn’t steal must be afraid of something.

A study published this September in Evolution and Human Behavior,1 led by Oded Ritov, a doctoral student in psychology at the University of California, Berkeley, adds a wrinkle that fear alone has trouble explaining. Twenty-six chimpanzees (fourteen females and twelve males, aged 16 to 39) were paired with a friend and with a non-friend, and the same animals were tested in both conditions. Thieves pulled the tray in 61% of trials with friends and 70% of trials with non-friends. Nine percentage points is a modest gap, and the authors report it as significant (χ²(1) = 7.57, p = 0.006) across 138 trials, in a design where each victim sat through one session of three trials with a friend and one with a neutral peer.

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A young ape alone on a branch with a hard fruit and a stick looks like the plainest possible case of an animal teaching itself. Most of us would file it that way, and so would a good share of the research on animal culture. That research has long sorted learning into two bins: social learning, picked up by watching others, and individual learning (sometimes called asocial), worked out by trial and error. The Suaq records suggest that the ape on the branch is usually still under the influence of something it saw. A single bout of watching can keep its hands busier than usual for more than two hours after it has looked away.

The study was published in Science1 on 24 September 2026. It was led by Revathe Thillaikumar, a Marie Skłodowska-Curie postdoctoral fellow at the Max Planck Institute of Animal Behavior in Konstanz, Germany (the paper credits her as T. Revathe). The senior author is Caroline Schuppli, who leads the institute’s Development and Evolution of Cognition Research Group. The learning data come from more than 1,700 hours of direct observation of 21 immature Sumatran orangutans (Pongo abelii), aged between about six months and eight and three-quarter years when they were watched. Two learning behaviors were counted. Peering is the field term for sustained, attentive, close-range watching of another orangutan, either the mother or another animal nearby, and the team treats it as the visible trace of social learning. Exploration, their marker for individual learning, is the handling and failed eating described above. Over the 12 years the team recorded 2,113 bouts of peering to set against the 4,649 of exploration.

A Sumatran orangutan infant is exploring a Neesia fruit by biting it, holding it, and placing it securely in the space between the trunk and branch of a tree, and then kicking it in an (unsuccessful) attempt to break open the fruit. Credit: Zul Zulmaidi, SUAQ Project

The reason to count stares and fumbles for that long is food. An adult Sumatran orangutan eats around 250 different items, picked from thousands of possibilities in the forest. Many of them need processing and a few need tools, and a youngster has about eight years at its mother’s side to learn them. The team measured how ready an animal was by the number of distinct foods it ate without its mother’s help by independence, which they call diet breadth. Nobody had measured how watching and exploring add up to that number in a wild animal, partly because years can separate a learning event from any change in an orangutan’s diet.

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Almost anyone reading that account sees grief in it, and behind the grief a mother who knows exactly what has happened. The reading has support among researchers. A team at Gombe National Park in Tanzania, led by Elizabeth V. Lonsdorf, then of Franklin and Marshall College in Lancaster, Pennsylvania, reported in 2020 that mothers there carried infant corpses at high rates even though their behavior suggested they recognized the deaths, and Lonsdorf proposed that the behavior might resemble human grief. The assumption most readers bring to Jire’s story goes a step further, to the idea that a mother who carries a body for two months must understand that her infant is gone for good. A new study in Biology Letters1 by Reece Hammond, a doctoral candidate, and Thomas A. Püschel, the Wendy James Associate Professor in Evolutionary Anthropology, both at the University of Oxford’s School of Anthropology and Museum Ethnography, finds that nothing in how long chimpanzee and bonobo mothers carry their dead requires that understanding, though nothing in it rules the understanding out either.

Chimpanzees and bonobos, the two living species in the genus Pan, are the closest living relatives of humans, and most researchers place the last ancestor all three shared somewhere between 6 and 8 million years ago. Primatologists study how Pan behaves around its dead because doing so helps separate the human responses to death we probably inherited from those that arose only in our own lineage. One part of a fully developed human concept of death is the knowledge that death cannot be reversed. If the length of an ape mother’s vigil can be explained without that knowledge, then the knowledge may be a later arrival, something that took shape among hominins after our line split from theirs (a possibility the Oxford authors put forward carefully, and which their data can support only indirectly).

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Teaching of that kind, where an adult changes what she does so that someone else can learn, is widely assumed to be a human specialty, and chimpanzees, in the familiar picture, learn tool use by watching and fumbling with nobody showing them anything. Christophe Boesch reported apparent teaching among nut-cracking mothers in Côte d’Ivoire’s Taï National Park in 1991, but such cases have stayed rare, and a study published on September 16, 2026, in Frontiers in Psychology1 adds two, with a tally that changes what chimpanzee teaching mostly looks like.

Soukki and Saïsaï are western chimpanzees (Pan troglodytes verus), a Critically Endangered subspecies, and they belong to a population of at least 53 adults in the Dindefelo Community Nature Reserve, more than 140 square kilometers of grassland and dry woodland in Senegal’s Kedougou region, along the border with Guinea. Nobody has ever fed or habituated them, so no one follows them with a notebook as Jane Goodall did at Gombe, in Tanzania; camera traps from Bushnell, Browning, and Wimius record a one-minute clip whenever something moves. Between 2017 and 2025, a team led by Andreu Sánchez-Megías, a doctoral candidate at the University of Barcelona who works with the Jane Goodall Institute Spain in Senegal, gathered 14 hours and 58 minutes of video at 14 spots where the chimpanzees fish for algae, dip for army ants, or fish for termites with sticks, and 30 minutes at 11 spots where they carry baobab fruit.

The question is whether giving away a tool costs the giver anything. In 1992 the biologists Tim Caro and Marc Hauser proposed that an animal teaches when it acts in a learner’s presence, pays a cost or at least gains nothing by it, and the learner learns, and in 2016 Stephanie Musgrave and colleagues used that test to argue in Scientific Reports that tool transfers among termite-fishing chimpanzees at Goualougo, in the Republic of the Congo, qualify.

The Dindefelo cameras caught 33 tool transfers, 19 during ant dipping, 10 during algae fishing, and four at termite mounds. Most of the chimps who started with the tool (initial possessors, in the paper; holders, here) were adults, and the largest group of recipients, 14, were infants. Of the 27 pairs that could be identified, 16 were relatives, eight of them mother to offspring. Soukki’s handover, which the paper classes as a proactive transfer, was the only one of the 33 that the holder started. In the other 32 the recipient moved first: 14 were recoveries, in which the recipient picked up a tool the holder had just set down and walked away from; three were fragments that fell from a tool still in use; 13 were tolerated takes, in which the recipient took the tool from the holder’s hands and the holder let go; and two were steals the holder failed to stop.

Ant dipping tool transfer. Credit: Jane Goodall Institute Spain in Senegal

Sánchez-Megías, who scored all the videos, compared each animal’s behavior in the 30 seconds before a transfer with the 30 seconds after, leaving out recoveries, since a chimp who has already walked away from a stick gives nothing up. Holders afterward spent less time using tools and made fewer insertions, while recipients spent more time with tools, made more insertions, and, in the stricter versions of the analysis, ate more mouthfuls per second. Of the 23 holders who stayed on camera long enough to follow, 13 quit using tools. The holders’ eating rate did not drop significantly, which the authors put down to small samples, and the strictest models rest on just four transfers.

The stick Soukki left was probably worth more than it looks, because the hard part of ant dipping at Dindefelo seems to be finding ants at all. The cameras at four ant sites logged 166 successful dipping events and 525 in which no ants were there, and a 2024 paper by Sánchez-Megías and colleagues in Communications Biology found that the chimpanzees remember the hidden underground nests of Dorylus army ants and return to check them across several years. TS1 is one they visit often. The ants bite, too; Soukki brushed them off her right leg on her way over to Saïsaï.

Baobab fruit transfer and pounding. Credit: Jane Goodall Institute Spain in Senegal

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A hub, in the vocabulary of connectome research, is not a metaphor stretched to fit the data. It means a region carrying a disproportionate share of a network’s total connections, the equivalent of a major interchange on a map of highways rather than a quiet residential street. Finding one in a chimpanzee or a macaque brain at all required Liu’s team to solve a harder problem than the scanning itself: brains of such different sizes and folding patterns do not line up point for point, so the group built what they call a shared homologous connectivity space, using white-matter tracts known to be conserved across all three species as a common coordinate system. Onto that shared space they mapped the human self-processing network, a set of regions defined years earlier by a meta-analysis of self-referential brain-imaging studies (one of the paper’s co-authors, Georg Northoff, published an influential meta-analysis of exactly that kind back in 2006,2 cataloguing which cortical regions activate when people think about themselves). Translating that human map onto a chimpanzee brain and then a macaque brain was closer to translating a poem between languages that share only some of their grammar than to overlaying two photographs.

Self, as a scientific object, splits fairly cleanly into layers that philosophers noticed well before anyone had a scanner to test them. There is a layer concerned with the state of one’s own body: hunger, pain, the thud of a pulse. There is a layer concerned with where that body ends and the world begins, the sense that lets a hand recognize itself as a hand even in the dark. And there is a layer concerned with something more abstract: a self that persists across time, has a name, and can answer, in the first person, when asked what it wants for dinner. Neuroscientists label these, respectively, interoceptive processing, exteroceptive processing, and mental self-processing, and until this study nobody had a good answer for whether the three layers evolved together, as one package, or separately, on different schedules, in different species.

The answer, once Liu’s group had enough data to give one, was neither of the tidy options: local tissue, the raw biological material of the self-processing network, stayed almost unchanged across the twenty-five to thirty million years separating the ancestors of macaques from the ancestors of every living ape, while the wiring connecting that tissue into a working system was substantially rebuilt, and rebuilt unevenly, with different layers of the self changing on different schedules.

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Adriano Lameira’s new paper in Biology Letters1 argues that this predicament, and not the demands of social life, is what set the ceiling on how many different sounds a primate species can make.

That claim runs directly at a result that has been load-bearing for two decades. In 2005, Karen McComb and Stuart Semple published a phylogenetically controlled analysis in the same journal showing that evolutionary increases in vocal repertoire size among nonhuman primates tracked increases in both group size and time spent grooming. It fit neatly inside the social brain hypothesis, Robin Dunbar’s proposal that the cognitive load of tracking many relationships is what drove primate brain expansion. More relationships, more brain, more to say. Language, on this account, is what happens when a lineage gets social enough.

Lameira rebuilt the dataset. He surveyed the literature for new repertoire descriptions published since 2005, ending up with 86 studies covering 77 species, taking the maximum reported repertoire estimate where multiple studies described the same species. Body mass and habitat classification came from Estrada and Marshall’s 2024 review of ground use across the primate order, which sorts species as arboreal (less than 10% of time on the ground), mixed (10 to 50%), or terrestrial (more than 50%). Brain masses came from six published sources, with gaps filled by allometric regression on log body mass; a leave-one-out validation on species with known brain masses returned a cross-validated R² of 0.936. Group sizes were compiled from field accounts and databases, using midpoints of reported ranges and typical party size for fission-fusion species. He then ran phylogenetic generalized least squares models over a consensus tree from 10kTrees, with log repertoire size as the response.

Brain size predicted nothing (t = -0.51, p = 0.61). Group size predicted nothing either, and the coefficient leaned negative (t = -1.74, p = 0.086). What came out significant was the interaction between body size and habitat use (p = 0.027), and it was driven entirely by the arboreal species. Among primates living in the canopy, the slope was 0.352: a 10% increase in body mass corresponds to a 3.5% larger repertoire, and a doubling of body mass to a 27.6% increase. Across a group spanning three orders of magnitude in mass, that is an enormous amount of variation accounted for by weight alone. In mixed-habitat and terrestrial species the relationship was not detectable at all.

The residuals tell a second story. After accounting for brain, body, and group size, species in mixed habitats carried repertoires roughly 17% above expectation, arboreal species about 8% above, and terrestrial species about 6% below. (The paper’s abstract gives slightly different figures for the arboreal and terrestrial categories, +6% and -3%, though the rank order is the same in both places.) The ordering that emerges is mixed, then arboreal, then terrestrial. The species that move between two structurally different worlds talk the most.

One caution before the interpretation: brain and body mass are tightly correlated across primates, as they are across mammals generally, so the finding is not quite that brains are irrelevant. It is that when body mass and brain mass compete to explain repertoire size, body mass wins, and by a reasonable margin (ΔAIC ≈ 5 in favor of the model retaining body size).

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The assumption goes like this: primates, and especially anthropoids (the group containing monkeys, apes, and humans), got smart because their frontal lobes got big. The frontal lobe handles planning, judgment, social reasoning, the stuff popular science writing likes to call “higher cognition.” It’s an intuitive story. It’s also, according to this new analysis, wrong, or at least badly incomplete.

Brains don’t fossilize. That’s the basic problem anyone working on the evolution of primate cognition runs into immediately. Soft tissue rots. What survives is bone, specifically the braincase, and researchers have long used the interior shape of that braincase to infer what the brain inside once looked like. The trouble is that inference from shape alone is subjective. You can look at a fossil skull, notice what seems like a bulging frontal region, and read a story into it that the data don’t actually support.

Kay’s team, working largely from a collection housed at the Duke Lemur Center Museum of Natural History, tried to get around that subjectivity by measuring rather than eyeballing. They micro-CT scanned a wide range of primate skulls, living and extinct, and built digital endocasts, then measured the volumes and surface areas of specific neocortical regions across the primate family tree. The goal was to see which parts of the brain actually grew disproportionately, and where, and when.

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That case sat buried in a 2006 paper for nearly two decades before a team led by Cyril Grueter at the University of Oxford pulled it into a much bigger picture. Grueter and his collaborators went looking for every documented instance they could find of primates forming friendly bonds with other species, combing scientific literature, media reports, and a survey sent to primatologists around the world. What came back was 427 cases spanning 88 primate species and 127 partner species, published this year in the journal Primates.1

The pattern that emerges from all that data is stranger than it sounds at first. Stump-tailed macaques in Thailand groom domestic dogs at a temple. Tufted gray langurs in Sri Lanka stroke giant squirrels. Snub-nosed monkeys in China play with pigs. Ring-tailed lemurs in Madagascar groom bamboo lemurs that aren’t even their own species of lemur. None of this is required for survival. Nobody’s getting fed, warmed, or protected from predators by doing it. It just happens, over and over, across unrelated lineages and continents, as if something in primate social wiring keeps reaching past the boundary of species without being told to stop.

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That observation, made by Jake Brooker and colleagues at Durham University, became the seed of a study just published in Proceedings of the Royal Society B.1 The question underneath it is simple enough to state and surprisingly hard to test: does touching each other before a fight over food actually stop the fight from happening?

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That’s roughly the shape of the pattern a team led by Odd Jacobson at the Max Planck Institute of Animal Behavior documented across fifteen years and about 30,000 hours of observation1 of 31 wild Pongo pygmaeus wurmbii mother-offspring pairs. It’s a strange thing to find in this particular species, because orangutans are supposed to be the antisocial great ape. Adult females spend most of their lives alone with a single dependent offspring, born once every 7.6 years on average, the longest interbirth interval of any land mammal. They don’t groom each other. They don’t build alliances. When neighboring mothers do cross paths, the encounters are brief, infrequent, and by most measures costly rather than beneficial to the mothers themselves.

So why would an animal built around solitude go out of its way to undo it, over and over, for years?

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That first idea, the “brain lag” hypothesis, had a rough two decades. In 1999,1 Robert Deaner and Charles Nunn ran the definitive test using a dataset of paired primate species, comparing how the ratio between brain and body mass changed against how long ago each pair had diverged from a common ancestor. Their logic was tidy. If body size changes first and brain size trails behind, then recently diverged species pairs should show brains that are too small for their bodies, while anciently diverged pairs should have had enough evolutionary time to correct the imbalance. Plot the residuals against divergence date and you should see a rising line.

They found nothing. No correlation for males, none for females, none when controlling for circadian patterns. The conclusion seemed airtight: brain and body size evolve together, in lockstep, under the same pressures. The idea of a lag quietly left the literature.

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The textbook story goes like this: human childbirth is uniquely difficult because evolution made two conflicting demands on our pelvis. Walking upright required a more compact, bowl-shaped pelvis. Growing a large brain required fitting a large-headed baby through it. The result is the obstetrical dilemma, a term introduced by Sherwood Washburn in 1960 and since reproduced in virtually every introductory physical anthropology course. Human babies are born neurologically helpless, the argument runs, because they have to exit before their skulls get too large to pass. Other primates, by contrast, face little or no obstruction at birth. Their birth canals are spacious relative to neonatal head size. The comparison makes Homo sapiens look like a species that evolution painted into a corner.

A new study in Nature Ecology & Evolution1 runs those numbers again, with better methods and a far wider sample, and finds that the story doesn’t hold.

The team, led by Nicole Torres-Tamayo and Lia Betti at UCL, analyzed pelvic morphology and neonatal head dimensions across 29 primate species using three-dimensional geometric morphometrics. The critical methodological move was abandoning the human-calibrated measurements that have shaped comparative anatomy since Adolph Schultz published his influential diagram of cephalopelvic proportions in 1949. Schultz’s approach measured the pelvic inlet the same way across all species, anchoring the anterior-posterior diameter between the top of the pubic symphysis and the sacral promontory. That works reasonably well for Homo sapiens, where bipedal adaptations have pulled the constraining sacral margin toward the inlet rim. In other primates, the sacrum sits higher relative to the pubis, meaning the actual narrowest point of the canal is lower down. Using the human landmark systematically overestimates available space in non-human species. The birth canal of a chimpanzee looks more capacious than it is. The same goes for monkeys.

The head measurement problem is equally significant. Schultz measured neonatal skulls in sinciput presentation, which means the forehead-to-occiput length forms one axis of the ellipse. Most primates don’t enter the birth canal that way. Geladas, baboons, squirrel monkeys, and macaques typically deliver face-first, with the neck extended, which presents a smaller cranial profile to the inlet. Homo sapiens delivers in occiput-anterior presentation, which similarly minimizes the dimensions that actually matter. When Torres-Tamayo and colleagues replaced sinciput measurements with species-appropriate face and occiput presentations, cephalopelvic mismatch decreased substantially across the board. But the correction fell disproportionately on species where the sinciput measurement was most unrealistic, making the old diagram’s claim of human exceptionalism look even more like an artifact of flawed calibration.

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A study published this month in Proceedings of the Royal Society B1 tries to answer exactly that question, and the answer is stranger than expected.

Eugene Melamud and colleagues at Calico Life Sciences, CleMetric, and the University of Wisconsin-Madison compiled lifespan records for 39 captive primate species from the Primate Aging Database, a decades-long accumulation of demographic data from zoos, research centers, and conservation sites across the United States and Europe. The dataset covers more than 12,000 individual animals, from lesser bushbabies to western lowland gorillas, with enough deaths recorded across most species to fit meaningful mortality models.

The framework they used goes back to 1825. Benjamin Gompertz, working from English mortality tables, noticed that the probability of dying doesn’t increase linearly with age — it accelerates exponentially. Starting around the time of sexual maturity, your risk of dying roughly doubles every several years. Gompertz captured this with a two-parameter model. One parameter, called the baseline hazard, describes how likely you are to die right at the onset of adulthood. The other, the aging rate, describes how quickly that probability climbs as you get older.

These two parameters are mathematically distinct and, it turns out, evolutionarily distinct as well.

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That is not a coincidence or a superficial resemblance. According to a new study in Communications Biology,1 the rhythmic structure underlying laughter has been present and conserved across all five lineages of extant great apes, including Homo sapiens, for at least 15 million years. The paper, led by Chiara De Gregorio, Marina Davila-Ross, and Adriano Lameira, is the first to conduct a comparative rhythm analysis of laughter across the complete set of living hominids: Pongo pygmaeus, Gorilla gorilla, Pan paniscus, Pan troglodytes, and Homo sapiens.

What they found is that every species laughs isochronously. The intervals between successive laugh bursts fall into a regular, evenly timed pattern, a 1:1 ratio between consecutive intervals. The “ha-ha-ha-ha” is not just phonologically similar across species. The beat is, at its core, the same.

An adolescent gorilla being tickled on his foot. The gorilla responds with laughter, pulls his foot away, but then presents his foot in order to be tickled some more. Credit: Dr. Marina Davila Ross

What Isochrony Reveals

Isochrony is a specific claim about timing. It means the intervals between sound onsets are metrically regular, not just roughly similar. Finding it in laughter across all five hominid lineages implies it was already present in the common ancestor from which orangutans diverged roughly 15 million years ago. The trait did not appear in chimps and then spread to humans, or emerge independently in multiple lineages. It was there from the beginning.

The team recorded 140 laughter bouts from 17 individuals across the five species, all young animals observed during playful interactions with familiar humans, in both tickling and spontaneous social play contexts. From these recordings, they extracted inter-onset intervals and computed what are called rhythmic ratios: the relative duration of one interval compared to the next. A ratio clustering around 0.5 indicates isochrony. Across all species, that’s what they found.

Bonobo laugh. Credit: Dr. Marina Davila Ross

Chimpanzee laugh. Credit: Dr. Marina Davila Ross

Gorilla Laugh. Credit: Dr. Marina Davila Ross

Orangutan Laugh. Credit: Dr. Marina Davila Ross

But the isochrony was not uniform across contexts. During tickling, laughter was highly regular. During social play, it deviated significantly. This is not surprising once you think about the mechanics: rough-and-tumble play involves torsion, compression, and impact on the thorax, which disrupts the respiratory cycle and with it the regular timing of vocalizations. Tickling laughter, produced without that physical interference, gave the researchers a cleaner window into the underlying rhythmic structure. It also gave them a methodological insight. If you want to study the evolution of the phonatory-respiratory system, tickling is the more stable condition.

The acceleration of laughter tempo across hominid evolution was also more clearly visible in tickling laughter than in play laughter. When the team modeled laughter tempo as a function of phylogenetic distance from Homo sapiens, the trend was statistically significant for tickling but not for play. The noise introduced by physical activity in social play effectively masked the evolutionary signal.

The Human Departure

Here is where humans become genuinely distinct, though not in the way that discontinuity narratives usually frame it.

Laughter has gotten faster across hominid evolution. It has also become more variable in its timing, with Homo sapiensshowing the highest coefficient of variation in inter-onset intervals of any species in the study. That variability is not random sloppiness. Research on human laughter perception suggests that variable timing is perceived as more socially and emotionally positive than rigid, stereotyped timing. A laugh that shifts and accelerates and varies across its duration reads differently from one that ticks along like a metronome. Humans have developed, it seems, not just faster laughter but more expressive laughter in the purely temporal sense.

More telling still is context sensitivity. Of all five species, only humans modulated laughter tempo according to context. When tickled, children in the study laughed faster than during social play. In the non-human apes, no such modulation was detected. This matters because it suggests an active, flexible vocal control that can respond to the social and emotional demands of a situation, rather than simply outputting a fixed motor pattern. The laughter you produce during tickling, where the rhythm is fast and regular, differs measurably from laughter in social play, and humans alone show that modulation.

This connects to a broader argument the study makes carefully. Human speech requires extraordinary fine-grained control over the timing and sequencing of vocalizations. That kind of control does not appear from nowhere. What laughter’s evolutionary record suggests is a long, gradual accumulation of rhythmic flexibility across the hominid lineage. Orangutans have isochronous laughter but little context sensitivity and relatively slow, consistent tempo. Moving along the phylogenetic tree toward the human branch, the rhythm becomes faster, more variable, and more responsive to context. Humans are at the far end of that trajectory, not standing apart from it.

Lameira and colleagues have been making versions of this argument for some time in relation to other orangutan vocalizations, including recursive vocal motifs and evidence of metered rhythm in Pongo song. What this study adds is comparative depth: every living hominid lineage, analyzed together for the first time, showing a coherent directional pattern across 15 million years of vocal evolution.

The study is appropriately cautious about sample sizes. Between two and four individuals per non-human species is a real limitation, and the authors acknowledge that future work with larger samples will refine species-level estimates of variability. The broader phylogenetic pattern is robust enough to survive that caveat, but species-by-species claims should be read with that constraint in mind.

What the data do not support is the older picture, still implicitly present in some accounts of language evolution, of a dramatic threshold crossing. Under that view, the crucial changes in vocal control were essentially a Homo sapiensdevelopment, qualitatively different from anything that came before. Laughter’s rhythm suggests something less abrupt: a long, incremental refinement of the same capacities that every great ape already possessed in some degree, with the human branch extending a trend rather than initiating one.

Sound does not fossilize. You cannot dig up a vocal tract from two million years ago and play it back. What you can do is listen to what all living hominids share, and trace the variations in what they do differently. The rhythm in an orangutan’s laughter during a tickling session is carrying information about a common ancestor that most people have never thought about. It is not a quaint analog of human behavior. It is a data point from 15 million years ago, still audible.

Further Reading

• Davila-Ross, M. J., Owren, M., & Zimmermann, E. Reconstructing the evolution of laughter in great apes and humans. Current Biology 19, 1106–1111 (2009). https://doi.org/10.1016/j.cub.2009.05.028

• De Gregorio, C., & Lameira, A. R. Twice times two: dual mechanism for double rhythmic meter in orangutans and the evolution of human song. iScience 29, 114273 (2026). https://doi.org/10.1016/j.isci.2026.114273

This is the adversarial context in which chimpanzees across Africa have developed what researchers call ant-dipping: the use of stick tools to harvest army ants, load them onto the stick, and pull them off with the free hand before eating. The technique varies across populations. Some communities use the pull-through method, sliding the loaded tool through a cupped hand. Others bring the stick directly to the mouth. Some use long tools; some use short

ones. Some communities in forest sites use a digging stick to widen the nest entrance before inserting the dipping tool, turning it into a two-stage tool set. A few populations, notably the Pan troglodytes of Taï Forest in Côte d’Ivoire, don’t use tools at all for certain ant species, simply grabbing brood by hand.

What’s driving all this variation? Ecology, culture, or some combination? That question is harder to answer than it sounds, because almost all the detailed work on ant-dipping has been done in forest habitats. Savanna populations have been underexamined. And chimpanzees are the only non-human ape that lives in open, hot, seasonally dry savannas at all — the kind of landscape that early hominins also occupied. If you want to understand what tool-using behavior looks like under those ecological pressures, savanna chimps are the only comparison available.

A study published in Scientific Reports1 in 2026, led by Andreu Sánchez-Megías and R. Adriana Hernandez-Aguilar at the University of Barcelona and the Jane Goodall Institute Spain, provides the first detailed account of ant-dipping in a savanna population. The site is Dindefelo, a community nature reserve in southeastern Senegal, covering about 140 square kilometers along the Guinea border. The climate is strongly seasonal, dry for roughly six months, with a mean annual temperature around 28.5°C. Evergreen vegetation — the moist, sheltered habitat army ants require — makes up less than twelve and a half percent of the landscape. Ants are scarce there. One of the lowest densities reported for the genus anywhere on the continent.

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There is a groove in the fossil record. A small, tapered notch, worn into the root surface of a tooth between two neighboring teeth. Researchers have been finding these marks in ancient human dentitions for over a century, and for most of that time the prevailing explanation has been a tidy story: our ancestors were picking their teeth. Sticks, fibers, bone fragments, whatever was at hand. One paper a couple of decades ago called it the oldest hominid habit. The grooves show up in specimens more than two million years old, in Neanderthal dentitions, in medieval European samples. The narrative held.

A new study published in the American Journal of Biological Anthropology1 hasn’t destroyed that narrative, but it has made it considerably harder to defend. What Towle, Krueger, and colleagues found, after examining 531 individuals from 27 wild primate species, is that these grooves are not unique to Homo. Wild apes and monkeys can develop them too. That’s the complication. The more striking finding, though, is the absence: not a single primate in the sample showed abfraction lesions, those deep, wedge-shaped notches at the gumline that are among the most common dental problems treated in modern clinics. Whatever is causing them, it appears to be something specifically wrong with how we live now.

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The setup is elegant in its simplicity. Each individual has an incentive to extract as much as possible. But if everyone does that at once, the resource collapses and everyone loses. Garrett Hardin’s famous 1968 formulation framed this as a structural inevitability, though researchers since Elinor Ostrom have documented in detail how humans develop norms, rules, and communication strategies to sidestep it. What no one had tested, until now, was how chimpanzees perform at this problem when grouped in more than pairs.

The answer, published in Communications Psychology1 by Kirsten Sutherland, Daniel Haun, and Alejandro Sánchez-Amaro, is surprising in two respects. First: chimpanzee quartets significantly outperformed dyads at keeping the resource open. Second: the mechanism behind that success was not what the researchers expected.

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