That specificity is what a new study1 from the University of Portsmouth set out to document. The question wasn’t simply whether great apes mirror each other’s facial expressions during play. That much was already known. The question was whether they do it exactly — matching the specific variant their partner used, the way a human spontaneously mirrors a Duchenne smile.

The answer, from a sample of 96 apes across two species and eight social groups, appears to be yes.

Diane Austry, lead author and now based at Durham University, along with a team including Marina Davila-Ross and Guillaume Dezecache, studied 39 Pongo pygmaeus at the Sepilok Orangutan Rehabilitation Centre in Malaysia and 57 Pan troglodytes at the Chimfunshi Wildlife Orphanage in Zambia. The animals were video-recorded during spontaneous social play, and their laugh faces — technically, open-mouth faces, or OMFs — were coded frame by frame at 25 frames per second. Each open-mouth expression was classified as either showing the upper teeth or not. Then the researchers looked at whether the observing animal matched the specific variant its partner had just produced, within three seconds of that production.

That three-second window matters. It spans both the rapid automatic response seen in less than a second, which is measured in facial mimicry research more broadly, and the slower delayed response. The average latency in this study was just over a second for both species: around 1.1 seconds mean, with more than half of all responses landing under one second.

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Two clusters of Pan troglodytes — chimpanzees who had shared the same territory, groomed each other, hunted together, and fathered offspring with the same females — approached one another near the center of their home range. They had done this countless times before. Fission-fusion sociality is the default mode for chimpanzees; groups split and reform constantly across the day. What should have happened was a reunion. Instead, the Western chimpanzees ran. The Central chimpanzees chased them. Then for six weeks, the two groups avoided each other entirely.

That had never been observed before in 20 years of continuous monitoring at Ngogo.

What followed over the next nine years is documented in a paper published this week in Science1 by Aaron Sandel, John Mitani, Kevin Langergraber, David Watts, and colleagues: the largest-ever recorded chimpanzee community fracturing permanently into two rival groups, followed by sustained lethal violence in which the smaller group killed at least seven adult males and 17 infants from the larger one. The team drew on 30 years of demographic records, 24 years of social network data, and a decade of GPS tracking. It is, by any measure, an extraordinary longitudinal dataset.

The Ngogo chimpanzees had been a single community since continuous research began in 1995. By the time the dataset opens, they numbered well over 100 individuals and would eventually peak near 200 — far larger than typical chimpanzee communities. Social network analyses using the Leiden algorithm revealed two loosely defined clusters, Western and Central, throughout this period, but cluster membership was fluid. About 29% of individuals switched clusters from one year to the next. Forty-four percent of infants born between 2004 and 2014 were conceived by parents from different clusters. The whole group shared a single territory and a single reproductive pool. They were, by every meaningful measure, one community.

Then the network shifted.

Three independent statistical methods all flagged 2015 as the sharpest structural transition in the 24-year record. Modularity spiked. The two clusters stopped bleeding into each other. A change-point analysis for longitudinal network data identified the transition as statistically unambiguous. What had been a fluid, overlapping social structure crystallized into two distinct blocs. By 2017, the Western and Central chimpanzees occupied largely separate ranges. By 2018, there were no affiliative relationships between members of the two groups, and reproduction between them had ceased entirely. The last cross-group conception had occurred in March 2015 — almost exactly when the behavioral break first appeared.

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Masripithecus moghraensis was recovered from Wadi Moghra, a fossil site in northern Egypt, during fieldwork in 2023 and 2024 by the Sallam Lab team from Mansoura University. The animal lived roughly 17 to 18 million years ago, in the Early Miocene. What the description in Science1 makes clear is that this is the first unambiguous fossil ape from North Africa. That gap in the record had gone mostly unremarked, because nobody had a good way to explain it. Now the explanation looks obvious in retrospect: nobody was looking in the right place.

What the teeth say

The jaw preserves enough to be diagnostic. The canines and premolars are notably large. The molars have rounded, heavily textured chewing surfaces. The whole structure is robust. Working from this anatomy, the research team interprets Masripithecus as a dietary generalist: primarily frugivorous, but built to crack harder foods when fruit was scarce.

Masripithecus reconstruction video. Credit: Professor Hesham Sallam

That dietary profile is not unusual for an ape. What is unusual is the geography and the timing. The Early Miocene was a period of climatic flux. Northern Africa and Arabia were becoming more seasonal. For an ape to have persisted this far north, flexibility would have been a genuine advantage. The anatomy of Masripithecus looks like exactly that kind of solution.

Masripithecus sculpting video, sculpting by Mohammed Hebeish. Credit: Professor Hesham Sallam

The genus name combines Masr, the Arabic word for Egypt, with the Greek píthēkos, meaning ape. The species name honors Wadi Moghra itself. Transparent and practical.

A missing piece hiding in plain sight

Early Miocene ape fossils have historically clustered in East Africa. Sites in Kenya, Uganda, and Tanzania have been the primary source of hominoid material for decades, and the field’s picture of where early ape evolution took place has been shaped accordingly. North African sites of comparable age had turned up cercopithecoid monkeys, but no apes. The prevailing interpretation was that apes simply hadn’t gotten there yet.

Masripithecus complicates that story considerably.

The team placed the new species in phylogenetic context using a Bayesian tip-dating analysis that combined morphological data from living and extinct apes, molecular data from living species, and the geological ages of fossils. The result positions Masripithecus closer to crown Hominoidea than any of the coeval East African fossil apes. Crown Hominoidea is the group containing all living apes and their last common ancestor: gibbons, orangutans, gorillas, chimpanzees, and humans.

That finding has direct implications for where crown Hominoidea originated. Erik Seiffert, a paleontologist at the University of Southern California and co-author of the study, put it plainly: “For my entire career, I considered it probable that the common ancestor of all living apes lived in or around East Africa. But this new discovery, and our new and novel analyses of hominoid phylogeny and biogeography, now strongly challenge that idea.” He has also noted that the strength of the biogeographic scenario does not actually depend on Masripithecus alone, but that the new fossil is very much consistent with it.

The biogeographic analyses point toward northeastern Afro-Arabia as the most probable ancestral homeland. During the Early Miocene, the African and Arabian plates were in their final phase of collision with Asia. Fluctuating sea levels periodically opened land connections across what is now the eastern Mediterranean and Middle East. This region functioned as a corridor. Animals could move through it when conditions allowed.

Masripithecus, positioned where it is phylogenetically, represents a link between the African fossil record and the Eurasian one. Hominoid fossils appear in Europe and Asia from the Middle Miocene onward, and the question of where those animals came from has generated sustained debate. The Egyptian ape does not resolve that debate entirely, but it fills a gap that had been invisible. The corridor was not empty. It had apes in it.

The problem with only looking where the fossils are

The deeper issue this raises is methodological. Paleontology works with what it has, and for decades what it had was concentrated in East Africa. That is partly because East Africa is genuinely rich in fossil hominoids, and partly because sustained fieldwork there has built the infrastructure, expertise, and permit histories that attract more fieldwork. North Africa, by contrast, was less systematically explored for Miocene hominoids. Absence was treated as data when it was likely a sampling artifact.

Sallam’s team spent five years looking for this material. The payoff is not just a new species. It is a reorientation of the question itself. If the common ancestor of living apes lived in northeastern Afro-Arabia, and if that region has been chronically underexplored, then the actual shape of early hominoid diversification may look substantially different from what the current fossil record suggests.

There is more to find. The Wadi Moghra jaw is a reminder that a blank space on a distribution map is not the same thing as an empty landscape.

What followed was not a clean scientific resolution. It was a war.

The term “ape culture wars” was coined by primatologist William McGrew in 2003, but the conflict it names has older roots. In its early form, the question was binary: do non-human great apes have culture or not? Field researchers — biologists and primatologists who spent their careers watching chimpanzees in Gombe, Taï, Mahale, and Bossou — tended to say yes. Psychologists running experiments with captive apes in laboratories tended to be more skeptical, or at least more demanding in what they’d accept as evidence. Two research communities, two methodological traditions, and a fundamental disagreement about what counted as proof.

That version of the war is largely over. The evidence for cross-population behavioral differences in Pan troglodytes — differences that can’t be explained by genetics or ecology alone — has accumulated to the point where most researchers across both camps now accept that great apes have cultures of some kind. The same has been documented in Pongospecies, in bonobos, and to a lesser extent in gorillas. Indirect evidence for social learning, the mechanism typically taken as culture’s precondition, is also documented in capuchins, macaques, cetaceans, birds, and apparently even bumblebees.

The question “do apes have culture” has been replaced by a thornier set of questions: what kind of culture, transmitted through which mechanisms, producing which kinds of products? This is where the current war is being fought, and in a 2026 paper in Evolutionary Human Sciences,1 primatologists Ammie Kalan and Claudio Tennie attempt something unusual — a diagnosis from both sides simultaneously. Kalan works primarily with wild apes; Tennie primarily with captive ones. Their paper is part historiography, part peace treaty, and part metacritique of a field they argue has allowed genuine scientific divisions to calcify into something more tribal.

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But biology is rarely that tidy. New research from a team at the University of Geneva suggests that this neural real estate is less of a private club and more of an ancestral inheritance. When we hear the hoot of a chimpanzee, our temporal voice areas react with a selective intensity that was previously thought to be reserved only for Homo sapiens.

This isn’t just a general reaction to noise. The researchers1 used fMRI to watch the brains of 23 participants as they listened to a variety of primate calls: humans, rhesus macaques, bonobos, and chimpanzees. Even after the team mathematically stripped away the basic acoustic differences like pitch and loudness, a specific subregion in the anterior superior temporal gyrus remained stubbornly active for chimpanzee vocalizations.

It appears that our “human” voice areas are actually tuned to a broader frequency range that includes the sounds of our closest evolutionary neighbors. Interestingly, this neural kinship did not extend to bonobos. Despite being just as closely related to us as chimpanzees, bonobo calls failed to trigger the same specialized response in the human TVA.

The Acoustic Gap

The reason for this distinction likely lies in the anatomy of the throat. Bonobos have a shorter larynx, which gives their vocalizations a much higher fundamental frequency than those of humans or chimpanzees. Chimpanzee voices, by contrast, sit much closer to our own acoustic “sweet spot”.

The researchers hypothesized that the human auditory cortex evolved a tonotopic map tailored to the specific frequencies of human speech. Because chimpanzee calls fall within or near that range, our brains process them using the same specialized machinery we use for our parents, friends, and strangers on the street. Bonobos, through a process of evolutionary neoteny—the retention of juvenile traits into adulthood—seem to have drifted away from that shared acoustic space. Their calls are simply too high-pitched for our voice-processing hardware to recognize them as “voice-like”.

This finding challenges the idea of human “uniqueness” in brain organization. If our voice-sensitive areas are also chimpanzee-sensitive, it suggests that these regions didn’t appear out of nowhere to support human language. Instead, they likely represent an ancient system for social monitoring that we share with the other great apes. We didn’t build a new room for the human voice; we just redecorated an existing one.

Evolutionary Echoes

This leaves us with a compelling question about the nature of our own perception. When we hear a chimpanzee, are we hearing an “animal,” or is our brain instinctively categorizing that sound as a kind of distorted, familiar “other”?

The data showed that while the human voice still generates the most widespread activity across the temporal cortex, the anterior subregions of the TVA are remarkably sensitive to these cross-species similarities. It is as if the back of the brain handles the complex nuances of human identity and emotion, while the front remains vigilant for the basic, structural signatures of a primate throat.

We often think of our brains as being uniquely adapted to the modern world, but studies like this remind us that we carry deep, prehistoric echoes in our anatomy. Our “human” brain is still, in many ways, a primate brain, reaching out across six million years of separation to recognize the sound of a cousin.

A team led by Christopher M. Smith and Jeffrey T. Laitman recently analyzed1 the inner ears of 14 primate species, including the agile gibbon and the upright Homo sapiens. They used 3D imaging to map the delicate landmarks of the bony labyrinth, the hard shell that houses our sensory organs. Their goal was to see if the balance half of the ear is actually a single unit or if it is made of independent parts.

The team found that the vestibular system is not a monolith. It is modular.

A Third Room in the Labyrinth

In the traditional view, the semicircular canals and the otolithic organs are grouped together as one peripheral vestibular system. The canals are the gyroscopes that detect rotation, while the otolithic organs, the utricle and saccule, detect linear movement and the constant pull of gravity. We have often assumed that these parts evolve in lockstep. If an animal develops larger canals to handle acrobatic movement, we assumed the rest of the vestibular system grew with them.

Smith and his colleagues found that this integration is a myth. Their statistical analysis of species like Pan troglodytesand Gorilla gorilla showed that the canals and the otoliths are semi-independent modules. They follow different evolutionary trajectories and respond to different selective pressures. The researchers propose a tripartite model instead: a cochlear system for hearing, a canalicular system for rotation, and an otolithic system for gravity.

This shift in perspective is more than an academic reclassification. It reveals that our balance system has a hidden flexibility. The different parts of the ear are evolvable on their own. This modularity allows a species to fine-tune its sense of gravity without necessarily changing how it senses a head turn.

The Independent Evolution of Gravity

The evidence for this decoupling is clearest when looking at our own lineage. Across the great apes, the otolithic system has undergone a large-scale increase in relative size. In the past, researchers noticed that catarrhine primates had enlarged vestibules, but they often dismissed this as a byproduct of semicircular canal enlargement.

This study suggests the opposite. The expansion of the vestibule in hominoids is an independent evolutionary event. It may be linked to the complex ways apes move through three-dimensional space, where sensing the orientation of the body relative to gravity is just as critical as sensing the speed of a swing.

There is also a deep history here that reaches back to the water. The otolithic organs in mammals still carry a shadow of their original function in fish as vibration detectors. Modern mammals can actually hear certain bone-conducted or airborne sounds through their otoliths. By treating these organs as a distinct system, we begin to see the ear not just as a balance sensor, but as an ancient, multi-purpose tool for navigating a physical world.

This tripartite model changes how we read fossils. When we find the petrous bone of an ancient primate, we can no longer look at one part of the vestibular system and assume it tells the whole story of how that animal moved. The canals might tell us about its agility, but the otoliths tell a separate story about its relationship with gravity. We are looking at two different evolutionary clocks ticking inside the same small bone.

A new comparative analysis published in Evolution Letters1 challenges that framing at its root. Working across 100 primate species including Homo sapiens, researchers from the University of Lincoln found that how frequently a species engages in everyday, non-lethal aggression tells you remarkably little about whether it kills conspecifics. Mild aggression and lethal violence appear to have followed different evolutionary trajectories. They are not the same trait in different intensities. They are, in a meaningful phylogenetic sense, different things.

The team, led by Bonaventura Majolo and Samantha Wakes, assembled data on five distinct types of aggression: between-group mild aggression, within-group mild aggression, between-group adulticide, within-group adulticide, and infanticide. The data covered wild, non-provisioned, group-living primates only — captive populations excluded — and drew on published literature spanning 1950 to mid-2022, supplemented by unpublished data gathered through a survey of primatologists. Thirty-nine researchers contributed data on 28 species. The final dataset represents 43 genera across 11 primate families.

The analytical framework was Bayesian phylogenetic modeling, which allowed the team to test the strength of evolutionary correlations between each pair of aggression types while controlling for shared ancestry and five socio-ecological variables: sexual dimorphism, within-group sex ratio, group size, dietary folivory, and degree of territoriality.

What phylogeny explains, and what it doesn’t

The first notable result is structural. Phylogenetic relatedness explains more variance in lethal aggression than in mild aggression. Infanticide shows the strongest phylogenetic signal among the five types; within-group mild aggression shows the weakest. This means the distribution of lethal behaviors across primate lineages maps more predictably onto evolutionary history than the distribution of everyday squabbling does. Species that kill tend to come from lineages where killing has occurred before. Species that bicker don’t show the same taxonomic clustering.

When the team looked at correlations between aggression types, a clear pattern emerged. The three lethal types — between-group adulticide, within-group adulticide, and infanticide — were positively and moderately correlated with one another. Species where adults kill members of rival groups are also more likely to kill members of their own group, and more likely to engage in infanticide. The correlation between within- and between-group adulticide was particularly robust, with around 97–98% of the posterior distribution pointing in the same direction across both the null and full models.

Mild aggression told a different story. Neither type of mild aggression showed a meaningful evolutionary relationship with any of the lethal forms. The credible intervals for those pairwise correlations straddled zero. In the full model controlling for socio-ecological variables, the relationship between between-group mild aggression and infanticide, for instance, dropped to near nothing. The team ran five different versions of the dataset — varying how mild aggression was calculated — and obtained consistent results throughout.

The sex-specific analyses added another layer. When lethal aggression was split by the sex of the attacker, the evolutionary correlations among male lethal behaviors were strong: male between-group adulticide, male within-group adulticide, and male infanticide were tightly linked. In females, the picture was murkier. Female lethal aggression types were weakly correlated in the null model, with only between- and within-group female adulticide showing a stronger relationship when socio-ecological controls were added. Male infanticide had the highest phylogenetic signal of any category tested, with phylogeny accounting for roughly 59% of variance.

What escalation models get wrong

Animal contest theory generally predicts that mild aggression can escalate to lethal violence under the right conditions: high-value resources, closely matched opponents, or situations where the cost of continued conflict falls below the cost of backing down. This is a reasonable prediction. But it implies that the two types of aggression share an underlying logic, that mild conflict and lethal conflict sit on the same decision tree.

The Lincoln study’s findings suggest the decision tree model may be misleading, at least at the evolutionary level. Primates that engage in frequent mild aggression are not simply primates running a higher baseline risk of eventual killing. The socio-ecological conditions that would need to align for escalation to happen are, in mildly aggressive species, rarely present. Alternatively, those species may have developed conflict management behaviors — reconciliation, third-party intervention, social constraints — that function as effective circuit breakers. The result is evolutionary decoupling: lineages that argue a lot did not produce lineages that kill a lot.

This has practical implications for how socio-ecological models are built. Classical frameworks for understanding primate social structure incorporate predictions about competitive intensity but say little about when, or whether, that competition tips into lethality. The new findings suggest those transitions operate under different logic than the mild aggression preceding them.

The data on infanticide versus adulticide also bear consideration. Across the full dataset, infanticide was present in roughly 65% of species, adulticide in about 20%. The gap is large. Part of the explanation is methodological: infanticide has been studied more systematically in primates, so the literature is more likely to capture its presence. But risk asymmetry also matters. Killing an infant carries a much lower cost to the attacker than killing a conspecific adult, where both parties face genuine injury risk. Adulticide, when it occurs, tends to require numerical advantage, often attacking with multiple individuals against a single target. The team notes that planning-intensive adulticide, involving coordination, advance positioning, and target selection, may require levels of proactive aggression that are rare outside Pan and Homo sapiens. For most non-human primates, lethal attacks on adults are more likely stochastic: an isolated individual caught in the wrong encounter at the wrong time.

There is a broader implication here for how scholars interpret violence statistics, including the kind of cross-cultural historical comparisons that underpin arguments about whether modernity has made humans less violent. Treating adulticide, infanticide, and inter-group killing as a single undifferentiated measure of violence may obscure more than it reveals. The three types are correlated, but moderately, and the correlation is weaker in females than in males. Rolling them together into one “violence score” risks producing conclusions that reflect the amalgamation rather than any underlying biological reality.

The study cannot address rates, only presence or absence of lethal aggression. Whether a species kills once across decades of observation, or kills regularly, might matter enormously for understanding adaptive value and evolutionary trajectory. That data simply does not exist for most species at the scale required. The number of primate species with continuous long-term research across multiple populations is small, and adulticide is precisely the kind of rare event most likely to be missed or underreported. The figures for how many species show adulticide should be read as conservative.

What the study does establish is that the question “are humans violent?” is poorly formed if it treats violence as a single trait. Whether Homo sapiens has an evolved tendency toward mild aggression is a separate question from whether we have an evolved tendency toward lethal aggression, which is a separate question from whether we kill adults versus infants, within our social groups or outside them. Those distinctions are not just semantic. They have different phylogenetic histories, different socio-ecological triggers, and apparently different evolutionary dynamics. A species can be argumentative without being murderous. A species can be murderous without being especially argumentative. The relationship between the two is not a gradient. It is, as the data suggest, close to zero.

Further Reading

• Gómez, J.M., Verdú, M., González-Megías, A., & Méndez, M. (2016). The phylogenetic roots of human lethal violence. Nature, 538(7624), 233.

• Gómez, J.M., Verdú, M., & González-Megías, A. (2021). Killing conspecific adults in mammals. Proceedings of the Royal Society B, 288(1955), 20211080.

• Lukas, D., & Huchard, E. (2014). The evolution of infanticide by males in mammalian societies. Science, 346(6211), 841–844.

• Lukas, D., & Huchard, E. (2019). The evolution of infanticide by females in mammals. Philosophical Transactions of the Royal Society B, 374(1780), 20180075.

• Wrangham, R.W. (1999). Evolution of coalitionary killing. American Journal of Physical Anthropology, 110(S29), 1–30.

• Wrangham, R.W. (2018). Two types of aggression in human evolution. Proceedings of the National Academy of Sciences, 115(2), 245–253.

• Wilson, M.L., et al. (2014). Lethal aggression in Pan is better explained by adaptive strategies than human impacts. Nature, 513(7518), 414–417.

• Pinker, S. (2011). The Better Angels of Our Nature: The Decline of Violence in History and Its Causes. Penguin.

• Dwyer, P., & Micale, M. (2021). The Darker Angels of Our Nature: Refuting the Pinker Theory of History & Violence. Bloomsbury Publishing.

Two of those primates have now given up a little more of their story. Researchers led by Siobhán B. Cooke of Johns Hopkins University have described the first known lower jaws of Stirtonia victoriae, an ancient relative of modern howler monkeys. The specimens were recovered from La Repartidora, a fossil locality in the La Victoria Formation, by Andrés Vanegas of the Museo de Historia Natural La Tatacoa. They sat in sediments dated between 13.3 and 13.6 million years old. The study, published in PaleoAnthropology1 in 2026, uses three-dimensional geometric morphometrics to analyze both the shape of the teeth and the overall form of the mandible, and the results are clear: S. victoriae was eating a substantial quantity of leaves, making it the earliest confirmed folivore in the platyrrhine record.

That’s a specific, bounded claim. But the implications spread outward in ways that matter for understanding how primate diversity in the New World actually developed.

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It’s a compelling story. It also turns out to be significantly wrong.

A study published in Science Advances1 in March 2026 looked at aggression across 22 zoo-housed groups of Pan troglodytes and Pan paniscus — 189 individuals in total, observed across 16 European facilities spanning more than a decade of data. Led by Emile Bryon and colleagues from Utrecht University and the University of Antwerp, the team tracked both contact aggression (biting, wrestling, hitting) and non-contact aggression (charges, chases, displays). After running the numbers through Bayesian social network analyses that controlled for group size, sex ratio, and group identity, they found no meaningful difference in overall aggression rates between the two species. Not in total aggression. Not in physical contact aggression either.

Chimpanzees are not more aggressive than bonobos. That’s the headline, and it’s worth sitting with for a moment.

The bonobo-as-peacemaker image wasn’t invented out of nothing. It came largely from the work of Frans de Waal and others who documented bonobo sociality with genuine rigor, and it was reinforced by the striking contrast with chimpanzee behavior documented at sites like Gombe and Kibale. Chimpanzees engage in intergroup raids. They commit infanticide. Males form coalitions that sometimes kill other males. None of that has ever been documented in bonobos. So the idea of a fundamentally less aggressive bonobo species has had, until recently, some empirical grounding.

But recent field observations have started to complicate the picture. One study comparing wild populations found that bonobo males at Kokolopori in the Democratic Republic of Congo were actually more aggressive than chimpanzee males at Gombe, roughly three times as aggressive by some measures. Another study found the opposite, with chimpanzee males at Kalinzu showing higher rates of contact aggression than bonobos at Wamba. The conflicting results don’t mean the measurements were wrong. They mean the categories might be.

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Within a week, four other chimpanzees in his group were doing the same thing.

Eleven days later, Juma escalated. He inserted a blade of grass into his rectum and left it hanging. By the end of the month, five individuals at the Chimfunshi Wildlife Orphanage Trust in Zambia were walking around with grass protruding from various orifices. None of them showed any signs of discomfort. No red skin, no diarrhea, no scratching. Veterinary staff observed nothing that would suggest the grass was addressing any physical complaint.

This is, on its face, absurd. But the absurdity is precisely what makes it worth taking seriously.

The researchers who documented this,1 led by Edwin van Leeuwen at Utrecht University, had 136 other chimpanzees across seven other social groups at the same sanctuary to compare against. Over about 1,100 hours of observation between May 2023 and October 2024, not one of those 136 individuals was seen doing anything like it. The grass-in-ear and grass-in-rectum behaviors were confined entirely to a single group of eight animals. The team ran network-based diffusion analyses, a statistical method that tests whether the order in which individuals pick up a behavior matches the social connections between them, and found 99% support for social transmission in both cases. The probability that these behaviors spread through independent individual discovery rather than copying was, effectively, negligible.

So. Chimpanzees (Pan troglodytes) copied a pointless behavior from each other. That is the finding. And it raises a question that, once you sit with it, gets genuinely strange: why would an animal copy something that does nothing?

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This keeps happening. Six quartz prisms at a Lower Acheulian site in India, between 150,000 and 300,000 years old. A fragment of transparent rock crystal in an Acheulian layer in Austria. Quartz crystals in strata at Wonderwerk Cave in South Africa, dated between 276,000 and 500,000 years before the present. And more recently, calcite crystals collected by early Homo sapiens in the Kalahari around 105,000 years ago — crystals that, again, were not used as ornaments or tools.

All of them euhedral. All of them well-formed, with clear crystal faces. All of them transported from their geological source to wherever hominins were sleeping.

The question nobody has had a good answer to is why.

A team of researchers led by Juan Manuel García-Ruiz at the Donostia International Physics Center in Spain recently published an attempt to get at this question from a different angle. Since you can’t run experiments with H. erectus, they ran them with Pan troglodytes — chimpanzees, our closest living relatives, from whom we diverged roughly six to seven million years ago. Their paper, published in Frontiers in Psychology1 in early 2026, describes what happened when they gave two groups of enculturated chimps access to crystals and watched carefully. What they found is genuinely strange…

Toti analyzing the shape of the crystal. Credit: Frontiers in Psychology (2026). DOI: 10.3389/fpsyg.2026.1633599

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Primatologists have been sorting macaques into grades of social tolerance for decades, a framework developed by Bernard Thierry based on 18 behavioral traits that co-vary across species: how often individuals reconcile after fights, how steep the dominance hierarchy is, how willing adults are to share food, how much kin bias shapes social networks. Grade 1 species sit at the intolerant end. Grade 4 species are the most tolerant. It is a useful framework, though not without critics who point out that collapsing multidimensional social variation into a single axis loses important nuance.

What nobody had done, until recently, was scan enough macaque brains across enough species to ask whether these behavioral grades leave a mark on the brain itself.

A team at the University of Strasbourg has now done exactly that. Led by PhD student Sarah Silvère and senior author Sébastien Ballesta, the researchers assembled post-mortem MRI data from 42 individuals representing 12 Macaca species, spanning all four tolerance grades. Some brains came from open-access databases; others were newly scanned from animals that had died of natural or accidental causes at the Centre de Primatologie in Strasbourg, including two species, Macaca tonkeana and Macaca thibetana, that had never been imaged before. They focused on two subcortical structures: the amygdala and the hippocampus. Their results, published in eLife1 in 2026, overturn a tidy assumption about what the amygdala is for.

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This is what graduate school looks like sometimes.

The target was the Ngogo community of Pan troglodytes schweinfurthii, eastern chimpanzees who have been observed and individually identified by researchers for over three decades. Maro, a UC Berkeley graduate student working with biologist Robert Dudley, needed urine. Not because anyone finds that particularly enjoyable, but because urine is the only practical way to answer a question that has been circling primate biology for years: are wild chimpanzees actually metabolizing significant quantities of alcohol from the fermented fruit they eat?

The answer, according to a paper just published in Biology Letters,1 is yes. Decisively.

Of 20 urine samples collected from 19 individually identified chimpanzees, 17 tested positive for ethyl glucuronide (EtG) at a threshold of 300 nanograms per milliliter. Ten out of 11 samples tested at the higher threshold of 500 ng/ml also came back positive. In clinical and forensic contexts for humans, 500 ng/ml is the cutoff used to rule out incidental or accidental alcohol exposure. Exceeding it means you drank. The chimps exceeded it.

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Which raises a question that a team of researchers from Italy, Belgium, and beyond decided to take seriously: if sex is communicative, what exactly is being communicated, and how?

The study, led by Martina Francesconi and Elisabetta Palagi at the University of Pisa and published in Evolution and Human Behavior,1 didn’t approach this from the angle you might expect. They weren’t primarily interested in who was having sex with whom, or under what social circumstances. They were interested in tempo. Specifically, the rhythm of repetitive movement during sexual activity, and what happens to that rhythm when facial expressions enter the picture.

The data came from detailed video recordings of bonobos in zoo settings, analyzed frame by frame. The precision matters here. You can’t eyeball rhythm. What looks like a steady pace to a human observer may contain real variation that only shows up when you quantify it. Yannick Jadoul, a data scientist at VUB whose contribution to the study was the quantification of that rhythm, was careful to note that this is rigorous pattern recognition, not the kind of AI most people picture. It’s systematic measurement of complex behavior, applied to a domain where impressionistic observation has limits.

What they found: the tempo of movement during bonobo sexual activity runs high, averaging around seven movements per second. That’s fast. And it tends to stay fast, which is interesting in itself.

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He didn’t hedge. He didn’t qualify it as “proto-culture” or “culture-like behavior.” He created a new word, karachua, to describe learned, acquired behavior transmitted through groups with continuous social living. This was distinct from bunka, the Japanese word for human culture with all its trappings of language and music and art. But it was culture nonetheless.

“It is clear that we must recognize culture (karachua),” Imanishi wrote, “which we once considered as human lifestyle, in animals closely related to us, like monkeys and other mammals, at least to some extent.”

The paper sat untranslated until 2024. By then, the debate over whether primates have culture had consumed decades of scientific energy, cycled through multiple frameworks, and landed roughly where Imanishi started.

That gap matters. Not just as a historical footnote, but because it reveals how our own cultural assumptions shape what we’re willing to see in other species. The story of how scientists came to accept primate culture is also a story about disciplinary blindness, translation barriers, and the slow collapse of a boundary we desperately wanted to maintain.

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This is not a party trick. Kanzi, a lexigram-trained bonobo living at a research facility, has done something that forces a rethinking of what cognitive abilities existed in the common ancestor we share with other great apes. In a study published in Science1 in February 2026, researchers Amalia Bastos and Christopher Krupenye documented Kanzi’s ability to represent pretend objects across three separate experimental paradigms. He tracked imaginary juice. He distinguished real grapes from pretend ones. He kept straight what was there and what was only supposed to be there.

The implications ripple outward. If a bonobo can do this, the capacity for what cognitive scientists call secondary representation likely existed in the last common ancestor of humans, chimpanzees, and bonobos, an animal that lived somewhere between six and nine million years ago.

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A new study published in the American Journal of Biological Anthropology1 suggests that interpretation needs to be reconsidered. The team examined over 500 teeth from 27 species of primates, living and extinct, all from wild populations. They found grooves that look almost identical to the ones attributed to toothpicking in human fossils. Same shape. Same location. Same fine parallel scratches. But these primates were not using toothpicks.

The study also looked for a different kind of lesion. Deep, wedge-shaped notches that form near the gumline, known as abfraction lesions. These are common in modern dental clinics, often blamed on tooth grinding, aggressive brushing, or acidic drinks. Dentists see them constantly. But in the entire primate sample, the researchers found none. Not one.

So the marks we thought were cultural might be natural, and the marks we see all the time in humans might be uniquely ours.

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Now a carefully designed experiment with chimpanzees suggests that some of the ingredients for sustainable cooperation predate Homo sapiens. In a new study1 from the Max Planck Institute for Evolutionary Anthropology and collaborators, chimpanzee groups faced a classic “common-pool resource” dilemma. The results point to an unexpected lesson. Bigger groups, when socially tolerant and guided by restrained leaders, outperformed smaller ones at keeping a shared resource available.

The findings offer a window into the social roots of cooperation and hint that some of the failures seen in human societies may not stem from group size alone, but from how power and tolerance are distributed within them.

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The study, published in npj Complexity,1 followed spider monkeys for seven years and applied network science to their social lives. The result is a portrait of a primate society that behaves less like a static troop and more like a circulating newsroom, where individuals carry partial stories and recombine them through constant reshuffling of social groups.

The findings add weight to a growing idea in behavioral ecology and human evolution: that collective intelligence can emerge from simple social rules. In this case, monkeys who rarely forage with the same partners twice appear to be doing something sophisticated. They are pooling what they know about where fruit trees are and when they are likely to ripen, producing a kind of shared, evolving knowledge of the forest.

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There is no branch in its hands. No careful testing of footing. Just a clean drop through open air before another limb catches the fall. To a human parent, it looks terrifying. To the researchers watching, it turned out to be the most revealing moment of all.

A new study in iScience1 shows that chimpanzee infants, not adolescents, are the biggest risk-takers in their society. The finding flips a long-held assumption about how risky behavior develops and offers a sharp new lens on what makes humans different.

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