Koshima macaques in 2026 are still doing what their ancestors started doing in September 1953 on the 32-hectare island off the southern coast of Kyushu: they are washing sweet potatoes in seawater before eating them. The behavior — first observed by a Kyoto University fieldworker named Mito watching a 1.5-year-old juvenile female named Imo carry a sand-covered sweet potato to a freshwater stream and rinse it clean — represents the single most consequential observation in the history of animal-culture research. The cumulative work that followed at the Koshima Field Station (now operated as part of the Wildlife Research Center at Kyoto University) produced the 1965 paper by Masao Kawai in the journal Primates (volume 6, pages 1-30) titled “Newly acquired pre-cultural behavior of the natural troop of Japanese monkeys on Koshima Islet” — the paper that founded the contemporary field of cultural primatology and that established the methodological framework within which the subsequent six decades of animal-culture research has been conducted. The most recent significant extension of the framework appears in the 2017 paper by Schofield, Watanabe, Tanaka, Suzumura, Suzuki, and Hill in Primates titled “Cumulative culture in nonhumans: overlooked findings from Japanese monkeys?” — extending the Koshima ethnography into the contemporary cumulative-culture debate that the comparative-cognition research community has been litigating across the past two decades.
The story of Koshima macaques in 2026 is the story of the longest continuously operated nonhuman primate research site in the world — 77 years of monitoring across multiple generations of identified individuals, with the cumulative observational record including 627 individually-identified monkeys across the period from 1948 through 2016 and continuing extensions through the 2020s. The contemporary research apparatus operating at Koshima includes the Wildlife Research Center of Kyoto University, the broader Kyoto University primatology research network that traces its institutional lineage back to Kinji Imanishi and the founding of Japanese primatology in 1948, and the international research consortium that has progressively integrated the Koshima dataset into the broader contemporary comparative-cognition framework characterizing cultural transmission across non-human species. The cumulative output of this research network has, across the past seven decades, progressively positioned the Koshima sweet potato washing tradition as the foundational empirical case in the contemporary animal-culture research literature — the case from which the methodological, theoretical, and operational frameworks of cultural primatology were developed.
Koshima Macaques in 2026: The Current State
The Japanese macaque (Macaca fuscata) is the northernmost-occurring non-human primate species in the world, distributed across the four main Japanese islands of Honshu, Shikoku, Kyushu, and the southern offshore islands including Yakushima (where the smaller subspecies Macaca fuscata yakui occurs) and Koshima itself. The species is colloquially known as the “snow monkey” in English-language popular accounts, reflecting the species’ famous hot-spring bathing behavior at the Jigokudani Yaen-Koen site in Nagano Prefecture. The Koshima population belongs to the Macaca fuscata fuscata subspecies and occupies the small islet that has been the species’ primary research site since 1948 — operating through the broader patterns of brain-body co-evolution that shape cognitive capacity across vertebrate lineages.
Koshima Islet is approximately 32 hectares in area, located approximately 200 meters from the mainland of Miyazaki Prefecture in southern Kyushu, with a maximum elevation of approximately 113 meters above sea level. The island and its resident Japanese macaque population were designated a National Natural Monument of Japan, providing the legal protection framework that has supported the multi-decade continuous research program. The contemporary Koshima population numbers approximately 100 individuals distributed across two troops that descended from the original population observed in 1948. The population peaked at approximately 450 individuals in 1999 before declining to its current size through a combination of natural demographic processes and the reduction in provisioning that the research team implemented to restore more natural ecological conditions on the small island.
The Wildlife Research Center, Kyoto University Koshima Field Station — established in 1968 on the mainland opposite Koshima Islet — provides the operational base for continuing research on the population. The field station hosts visiting researchers from the broader international primatology community, supports the multi-disciplinary research program characterizing the macaques’ behavior, ecology, genetics, demography, and cognitive infrastructure, and maintains the longitudinal individual-recognition database that supports the ongoing characterization of the population’s social structure and cultural transmission dynamics. The cumulative research output across the 77 years of continuous observation makes the Koshima study one of the longest-running longitudinal cognitive-research datasets compiled for any non-human animal population.
What Imo Actually Did in 1953
The behavioral innovation that initiated the Koshima macaques cultural tradition occurred in September 1953, approximately one year and ten months after the Kyoto University research team had begun provisioning the macaques on the Koshima beach with unwashed sweet potatoes. The provisioning had been implemented as a methodological intervention to bring the wild macaque troop down from the mountain and cliff-face habitat where direct observation was operationally difficult, and onto the beach where the researchers could maintain continuous visual monitoring of individual identified animals. The sweet potatoes were dumped directly on the sand, with the macaques expected to consume them along with whatever adherent sand and grit the surface of the tubers carried.
Prior to September 1953, the macaques had handled the sand-covered potatoes in several different ways. Some individuals used their hands to brush sand from the surface of the potatoes before eating. Others used their body hair to scrape the sand off. Others simply consumed the potatoes with the sand attached, accepting the grit as a tolerable consequence of the food being available at all. None of these baseline behaviors involved water — the macaques had not, across the year of provisioning that preceded Imo’s innovation, been observed to use water for any food-processing purpose.
In September 1953, the Kyoto University fieldworker Mito observed the 1.5-year-old juvenile female Imo carrying a sand-covered sweet potato away from the provisioning site, walking to a small freshwater stream that ran across the beach, and rinsing the potato in the running water before eating it. The behavior was, in operational terms, an act of novel behavioral innovation — the kind of individual-level cognitive flexibility documented across the small group of vertebrate species demonstrating sophisticated problem-solving capacity and supported by the cortical neural infrastructure characterized across primate lineages. Imo subsequently extended the behavior across the following months, eventually transferring the washing site from the freshwater stream to the seawater of the nearby ocean — a modification that produced an additional behavioral component: the seawater added a salty flavor to the cleaned potato, which the macaques apparently preferred. The modification from fresh-water rinsing to seawater dipping represents what the contemporary cumulative-culture research literature has characterized as a measurable transformation across generations — the original innovation (rinse in fresh water) progressively elaborated through cumulative cultural modification into a more complex multi-stage behavior (carry to sea, rinse, dip for salty flavor, re-dip during eating).
The 1965 Kawai Paper and the Birth of Cultural Primatology
The formal scientific characterization of the Koshima sweet potato washing behavior appears in the 1965 paper by Masao Kawai in the journal Primates (volume 6, pages 1-30) titled “Newly acquired pre-cultural behavior of the natural troop of Japanese monkeys on Koshima Islet.” The paper documented the behavior’s first appearance in 1953, its progressive spread through the troop across the subsequent decade, and the specific social-transmission channels through which the behavior moved from Imo to her family members, playmates, and the broader troop. The paper has been cited more than 689 times across the comparative-cognition research literature and remains the foundational reference for the concept of behavioral tradition in a non-human primate.
The structural significance of the Kawai 1965 paper for the contemporary animal-culture research framework operates across multiple dimensions. The paper provided the first empirically documented case of an identified individual innovating a novel behavior that subsequently spread through a wild non-human primate population via observable social-transmission channels — extending the conceptual framework that Kinji Imanishi and the early Kyoto University primatology school had been developing into the explicit empirical domain. The paper established the methodological framework for studying cultural transmission in wild populations — the combination of long-term provisioning, continuous individual identification, longitudinal behavioral monitoring, and detailed tracking of behavioral innovation and spread that has since been applied to multiple subsequent cultural-primatology studies including the chimpanzee tool-use tradition research at multiple field sites across Africa and the cetacean signature-whistle and coda-repertoire research at the Dominica Sperm Whale Project and other ocean-based research programs, and to the broader vocal-learning research framework characterized across multiple non-mammalian vertebrate lineages.
Kawai’s term “pre-cultural behavior” reflected the cautious empirical framing the early Japanese primatology school applied to the question of whether non-human primates could be said to possess “culture” in the same sense as humans. The “pre-cultural” framing left open the question of whether the observed behavioral inheritance involved the cognitive substrates that human cultural transmission requires. The subsequent six decades of comparative-cognition research have progressively narrowed the gap between human and non-human cultural transmission — with the contemporary research literature now treating the term “culture” as broadly applicable to socially-transmitted behavioral inheritance across multiple non-human species, while continuing to recognize specific cognitive and structural differences between human cultural transmission and the cultural systems documented in non-human species.
How the Tradition Spread Through the Troop
The transmission pattern that Kawai’s 1965 paper documented operated through two distinct social channels. The first transmission channel was kinship-based — Imo’s mother Eba adopted the sweet potato washing behavior shortly after Imo began performing it, and Imo’s siblings adopted it through their observation of both Imo and Eba. The kinship-based transmission produced the reverse-direction social learning that the early Koshima research treated as one of the most distinctive features of the cultural-transmission process: typical mammalian social learning operates from mother to offspring (vertical transmission downward), but the Koshima case documented offspring-to-mother learning (vertical transmission upward) — extending the cultural-transmission framework into what the contemporary research literature characterizes as non-vertical social learning channels.
The second transmission channel was playmate-based — juveniles approximately the same age as Imo (those born approximately 1950-1952) adopted the behavior through their direct social interactions with Imo during the play groups that juvenile Japanese macaques form. The playmate-based transmission spread the behavior through the juvenile cohort relatively rapidly during the years immediately following the 1953 innovation, operating through the broader mirror-neuron and observation-based learning infrastructure that has been characterized across vertebrate lineages. As these juveniles matured into adult females, they continued to perform the behavior and transmitted it to their own offspring through standard vertical transmission — producing the multi-generational persistence of the tradition across the subsequent decades of Koshima history.
The demographic pattern of adoption revealed several specific features that have informed the subsequent comparative-cognition framework. Adult males showed the lowest rates of adoption — many adult males who were already mature at the time of Imo’s innovation never adopted the behavior, even after observing other troop members performing it across multi-year periods. Adult females showed intermediate adoption rates, with most eventually learning the behavior but at slower rates than juveniles. Juveniles and infants showed the highest adoption rates, with the behavior becoming essentially universal among individuals born after the early-1960s spread period. The age-graded adoption pattern parallels the age-dependent learning sensitivity documented across multiple socially complex vertebrate species and provides one of the empirically clearest cases of cohort-specific cultural acquisition in a non-human primate population, paralleling the matrilineal acoustic-identity systems documented across cetacean species.
The modification process that the behavior underwent across the subsequent generations operated as a candidate case of cumulative culture. The original behavior (rinse in fresh water) was progressively modified through the addition of new behavioral components — carrying potatoes from the provisioning site to the water source over increasing distances, transferring from the freshwater stream to the saltwater sea, “seasoning” the potato by dipping it repeatedly in seawater between bites to maintain the salty flavor, and washing pebbles and other small objects in addition to food items. The cumulative modifications represented progressive elaboration of the original innovation across multi-generational timescales, producing behavioral complexity that no single innovator had introduced in a single step.
Wheat Sluicing: The Second Invention
Three years after the sweet potato washing innovation, Imo invented a second cultural behavior — the wheat sluicing technique that the Kyoto University researchers documented in 1956. The provisioning at Koshima had been expanded to include unhusked wheat grains scattered on the beach sand alongside the sweet potatoes. The macaques had been handling the wheat by picking up individual grains from the sand-and-grain mixture, with the grain-by-grain extraction being operationally tedious and producing substantial loss as macaques mixed sand with the wheat during the picking process.
Imo’s wheat sluicing innovation operated through a fundamentally different physical principle than the sweet potato washing. The macaque scoops up a handful of mixed wheat and sand, walks to the water’s edge, and throws the mixture into the water. The wheat grains float on the surface (because wheat is less dense than water), while the sand sinks (because sand is denser). The macaque then skims the floating wheat from the water surface and consumes it without the sand contamination that the original ground-level picking method produced. The technique requires the macaque to understand — at least operationally — the buoyancy difference between wheat and sand, the spatial transformation that throwing the mixture into water produces, and the harvesting technique required to recover the separated wheat from the water surface.
The wheat sluicing technique is operationally more complex than the sweet potato washing technique. It involves multiple distinct behavioral components (scoop, transport, throw, wait for separation, harvest from surface) rather than the single dipping action that potato washing required. It depends on a physical principle (density difference producing buoyancy separation) that is more abstract than the simple rinsing principle that potato washing applied — operating through the elaborated sensory umwelt and physical-cognition infrastructure that primate species apply to their environment. The wheat sluicing also subsequently spread through the troop along similar transmission channels to the potato washing — kinship lines and playmate networks — but at a slower rate and with lower ultimate adoption frequency than the potato washing achieved. The 2017 Schofield et al. paper characterized the wheat sluicing as one of the candidate cases for cumulative culture in a non-human primate, arguing that the complexity of the behavior (and its progressive elaboration over time, including the use of nearby pools and rocks for the separation step in later generations) meets the criteria the contemporary cumulative-culture research literature has applied to candidate non-human cases.
Kinji Imanishi and the Founding of Japanese Primatology
The institutional and intellectual context within which the Koshima discovery occurred was established by Kinji Imanishi (1902-1992), the Kyoto University ecologist who founded the contemporary field of Japanese primatology in the late 1940s and early 1950s. Imanishi’s research program at Kyoto University combined the long-running ecological and evolutionary research tradition of Japanese natural history with a deliberately developed methodological framework that emphasized long-term behavioral monitoring, provisioning to habituate subjects for closer observation, and individual identification of every animal in the study population. The methodological triad has subsequently been applied to multiple primate and non-primate field-research programs across the past seven decades and has become the operational standard for longitudinal vertebrate behavioral research.
Imanishi’s theoretical contribution to the cultural-primatology framework operated through his early conceptual writings on “the evolution of human nature” (Imanishi 1952, published in Japanese in the volume Ningen). Imanishi proposed — well before the Koshima sweet potato washing discovery — that non-human primates might possess culture analogous in operationally relevant ways to human culture, with cultural transmission, behavioral inheritance, and population-level behavioral diversity as candidate empirical phenomena that could be investigated through systematic long-term observation. The theoretical framework challenged the prior conceptual divide between human cognition and the alternative learning and memory architectures documented across non-human species. The Koshima discovery in 1953 provided the first empirical confirmation of Imanishi’s theoretical framework, with the subsequent decades of Koshima research progressively validating the framework’s predictions about behavioral inheritance and cultural transmission in a wild primate population.
The Kyoto University primatology school that developed under Imanishi’s leadership included multiple subsequent researchers who became influential in the broader field. Junichiro Itani extended Imanishi’s framework to chimpanzee research in Tanzania and contributed to the comparative-cognition framework that subsequently characterized cultural transmission in great apes. Masao Kawai authored the foundational 1965 Koshima paper. Syunzo Kawamura documented additional Japanese macaque behavioral traditions at multiple research sites. Toshisada Nishida founded the Mahale Mountains chimpanzee research site that produced subsequent landmark cultural-primatology findings. Tetsuro Matsuzawa has continued the Kyoto University primatology tradition into the contemporary era through research on cognition in chimpanzees and on the continuing Koshima dataset. The institutional lineage represents one of the most coherent and continuous research traditions in the contemporary comparative-cognition research community, with the Koshima site serving as the historical anchor for the broader Kyoto University primatology school’s intellectual identity.
Cumulative Culture: The 2017 Schofield Reanalysis
The most consequential recent extension of the Koshima macaques research framework appears in the 2017 paper by Daniel P. Schofield and collaborators titled “Cumulative culture in nonhumans: overlooked findings from Japanese monkeys?” published in Primates (DOI 10.1007/s10329-017-0642-7). The paper revisited the multi-decade Koshima ethnography to evaluate whether the documented food-washing behaviors meet the contemporary criteria for cumulative culture — the increasing complexity or efficiency of cultural behaviors additively transmitted over successive generations that has been characterized as a hallmark of human cultural evolution.
The paper’s central argument was that the Koshima behaviors show progressive elaboration across the multi-decade transmission record that is consistent with cumulative cultural inheritance. The original 1953 sweet potato washing innovation (rinse in fresh water) progressively elaborated through cumulative cultural modification into more complex multi-stage behaviors including the seawater dipping for salt flavor, the carrying-distance extensions, the seasoning behavior of intermittent re-dipping during eating, and the application of the technique to additional food types beyond the original sweet potatoes. The 1956 wheat sluicing innovation similarly elaborated through cumulative cultural modification into more complex variants using rock pools, anticipatory positioning at the water’s edge, and other elaborations that the multi-decade observational record documented.
The structural significance of the Schofield et al. 2017 reanalysis is that it directly challenged the prior consensus in the comparative-cognition research community — which had held that only humans show cumulative culture in the sense of progressive complexity additively transmitted across generations. The reanalysis argued that the Koshima record, when examined across its 60+ year multi-generational span, shows the kind of progressive elaboration that meets the contemporary cumulative-culture criteria. The argument has not been universally accepted in the contemporary research community — multiple subsequent papers have continued to question whether the Koshima behaviors meet the strict definitional criteria the cumulative-culture framework applies, and the debate remains active in the contemporary cultural-evolution research literature. But the Schofield et al. 2017 paper successfully reopened the question and has informed the subsequent comparative-cognition framework on the question of where in the animal kingdom cumulative cultural transmission can be empirically documented.
The Koshima Field Station and Continuing Research
The Koshima Field Station of the Kyoto University Wildlife Research Center continues to operate in 2026 as the primary infrastructure for ongoing research on the Koshima macaque population. The station, built in 1968 on the mainland coast opposite the islet, hosts visiting researchers from the international primatology community and maintains the longitudinal individual-recognition database that supports the continuing characterization of the population’s social, behavioral, and demographic dynamics. The contemporary research program at the station includes work on personality assessment in Japanese macaques (paralleling the personality-research framework that the Arashiyama research group at the Iwatayama Monkey Park near Kyoto has developed), sensitivity to human gaze and visual perspective (documented in the 2021 paper by Castellano-Navarro et al. in Scientific Reports with collaboration between the Kyoto University Primate Research Institute and the Max-Planck Institute for Evolutionary Anthropology), cognitive ecology of the population’s foraging and social behavior, and demographic monitoring of the continuing multi-generational population dynamics.
The contemporary research output continues to integrate the Koshima dataset with the broader comparative-cognition framework characterizing cognitive performance across multiple non-human species. Recent research has extended the framework into the explicit examination of how the Koshima macaques’ social-cognitive infrastructure parallels or differs from the cognitive performance documented in other socially complex non-human primates and in the broader vertebrate cognitive-research literature including the corvid lineage demonstrating sophisticated cognitive performance comparable to that of the great apes, the parrot lineage demonstrating ape-like cognitive performance through the kea and African gray parrot model species, and the cetacean lineage demonstrating the most sophisticated non-primate communication systems documented in non-human animals.
The cumulative continuity of the research program — 77 years of continuous monitoring at Koshima Islet, with the original 22 individually-identified macaques from 1952 now succeeded by multiple generations of descendants — represents one of the most extensive longitudinal datasets compiled for any non-human vertebrate species anywhere in the world. The dataset includes individual-level life history data on 627 monkeys across the 1948-2016 period (with continuing additions through the 2020s), multi-generational pedigree information across the entire population, behavioral records on the cultural-transmission dynamics across 70+ years of the sweet potato washing tradition, and the longitudinal demographic record characterizing the population’s response to provisioning changes, environmental variation, and inter-troop social dynamics.
Stone Handling and Other Japanese Macaque Traditions
The Koshima sweet potato washing is not the only behavioral tradition that has been documented in Japanese macaque populations. Multiple subsequent studies have characterized additional cultural behaviors across Japanese macaque troops at sites including Arashiyama (Kyoto), Jigokudani (Nagano), Shodoshima Island, Takasakiyama, and additional sites across Japan. The cumulative documentation has produced one of the most comprehensive records of non-human primate behavioral diversity compiled for any single species.
Stone handling behavior — first documented at the Arashiyama B troop in 1979 — represents one of the most extensively studied Japanese macaque traditions outside the Koshima sweet potato washing case. The behavior involves the gathering, picking up, scattering, rolling, rubbing, clacking, carrying, and cuddling of stones in a non-adaptive solitary play context. The behavior was characterized across multiple subsequent studies by Michael Huffman and Jean-Baptiste Leca, who documented the behavior’s progressive spread through the Arashiyama troop across the period from 1979 through 1984 (reaching approximately 49 percent of the 236-member troop) and its subsequent transmission to additional Japanese macaque troops at multiple research sites. The 2007 Leca, Gunst, and Huffman paper in Behaviour (volume 144, pages 251-281) documented inter- and intra-troop behavioral variability of stone handling patterns across 10 troops — establishing the empirical foundation for treating stone handling as a population-level cultural tradition rather than as a species-typical behavior.
Hot spring bathing at the Jigokudani Yaen-Koen site in Nagano Prefecture represents another well-documented Japanese macaque tradition. The behavior was first observed in 1963 and has subsequently become one of the most photographed wildlife behaviors in the world — the iconic image of Japanese macaques bathing in steaming hot pools surrounded by winter snow has appeared across countless popular and scientific accounts of the species. The behavior spread through the local troop across the subsequent decades through social-transmission channels paralleling the Koshima sweet potato washing case, and has subsequently been documented as a localized population-specific tradition that distinguishes the Jigokudani troop from other Japanese macaque populations that do not bathe in hot springs despite living in similar climatic conditions.
The inter-troop and inter-site behavioral diversity that the cumulative Japanese macaque research has documented provides one of the empirically clearest cases of population-level cultural variation in a non-human primate species. Different troops show different behavioral traditions — sweet potato washing at Koshima, stone handling at Arashiyama, hot spring bathing at Jigokudani — that are not explained by genetic differences, ecological constraints, or developmental factors. The behavioral diversity meets the contemporary criteria for cultural variation in a non-human species and provides one of the empirically clearest cases of population-level behavioral inheritance operating through cultural-transmission mechanisms.
The Significance: Why Koshima Changed Everything
The structural significance of the Koshima macaques research program for the contemporary comparative-cognition framework extends across multiple dimensions that the prior research literature had not anticipated. The discovery refuted the prevailing mid-twentieth-century consensus that culture was uniquely human — a consensus that had been articulated across multiple disciplines including anthropology, psychology, philosophy of mind, and the biological sciences. The empirical demonstration that a wild non-human primate population could acquire, transmit, modify, and maintain a novel behavior across multiple generations through observable social-learning channels forced reconsideration of the conceptual frameworks that the prior research community had used to characterize the human-nonhuman cognitive boundary.
The Koshima discovery also established the methodological framework that has been applied across the subsequent six decades of cultural-primatology research. The combination of long-term provisioning to enable habituation, continuous individual identification of all population members, longitudinal behavioral monitoring across multiple generations, and detailed tracking of behavioral innovation and spread has been applied to multiple subsequent cultural-primatology studies including the chimpanzee tool-use traditions documented at Mahale Mountains, Gombe, Bossou, and Taï Forest, the orangutan tool-use traditions documented at multiple Sumatran and Bornean field sites, the various capuchin tool-use traditions documented in South American populations, and the broader cultural-primatology research program that has progressively characterized behavioral inheritance across multiple non-human primate species.
The Koshima research also established the conceptual framework within which the contemporary animal-culture research literature operates. The concepts of behavioral innovation, social transmission, cultural inheritance, population-level cultural variation, and cumulative cultural elaboration were progressively developed through the Koshima research and subsequently applied to multiple other species and research contexts. The contemporary comparative-cognition framework — which characterizes cultural transmission as a phenomenon distributed across multiple non-human species including primates, cetaceans, corvids, parrots, elephants, and additional vertebrate taxa — operates within a conceptual scaffolding that the Koshima research originated and that the subsequent decades of comparative work have progressively extended.
The cumulative impact of the Koshima research on the contemporary comparative-cognition framework is therefore difficult to overstate. The 1953 observation of a 1.5-year-old juvenile female carrying a sand-covered sweet potato to a freshwater stream initiated a research program that has progressively transformed the contemporary scientific understanding of the cognitive substrates of culture, the taxonomic distribution of cultural transmission, and the operational mechanisms through which behavioral inheritance maintains population-level behavioral diversity across multi-generational timescales in non-human species.
What Koshima Macaques in 2026 Actually Demonstrate
The cumulative weight of the contemporary Koshima macaques 2026 research record — the September 1953 observation by Kyoto University fieldworker Mito of the 1.5-year-old juvenile female Imo washing a sand-covered sweet potato in a freshwater stream on the beach of Koshima Islet, the subsequent 1956 invention by Imo of the wheat sluicing technique using density-based separation in water, the multi-decade documentation of the cultural-transmission process by Kinji Imanishi, Junichiro Itani, Masao Kawai, Syunzo Kawamura, and the broader Kyoto University primatology school across the period from 1948 through the contemporary era, the 1965 Masao Kawai paper in Primates (volume 6, pages 1-30) titled “Newly acquired pre-cultural behavior of the natural troop of Japanese monkeys on Koshima Islet” establishing the foundational empirical framework for cultural primatology with more than 689 subsequent citations across the comparative-cognition research literature, the demonstrated transmission patterns operating through kinship channels (Imo’s mother Eba and siblings) and playmate channels (juveniles of similar age cohorts) with measurable age-graded adoption rates showing adult males as lowest adopters and juveniles as highest adopters, the multi-generational modification process producing the cumulative elaboration from fresh-water rinsing to seawater dipping for salt flavor to inter-bite re-dipping for sustained flavor, the 2017 Schofield, Watanabe, Tanaka, Suzumura, Suzuki, and Hill paper in Primates (DOI 10.1007/s10329-017-0642-7) revisiting the Koshima record as a candidate case for cumulative culture in a non-human species and challenging the prior consensus that cumulative culture is uniquely human, the 1968 establishment of the Koshima Field Station of what is now the Wildlife Research Center of Kyoto University on the mainland coast opposite Koshima Islet, the cumulative 627 individually-identified Japanese macaques across the period from 1948 through 2016 with continuing additions through the 2020s, the population peak of 450 individuals in 1999 and the contemporary population of approximately 100 individuals distributed across two troops on the 32-hectare islet 200 meters from the Miyazaki Prefecture mainland in southern Kyushu, the National Natural Monument designation of Koshima Islet and its resident Japanese macaque population providing the legal protection framework that has supported the continuous research program, the broader Japanese macaque cultural research record including the 1979 Arashiyama stone handling tradition documented by Michael Huffman and Jean-Baptiste Leca, the 1963 Jigokudani hot spring bathing tradition that has become one of the most photographed wildlife behaviors in the world, and the cumulative inter-troop and inter-site behavioral diversity providing one of the empirically clearest cases of population-level cultural variation in a non-human primate species — represents a research record that is, in its operational density and empirical clarity, the foundational case in the contemporary animal-culture research literature.
The Koshima macaques of 2026 are still washing sweet potatoes in the seawater off the southern coast of Kyushu. The behavior has persisted across more than 70 years and multiple generations of monkeys descended from the original 22 individuals identified in 1952. The wheat sluicing technique continues to be performed by the contemporary population members. The cultural-transmission mechanisms that the 1965 Kawai paper characterized continue to operate across the contemporary multi-generational population. The Koshima Field Station continues to host visiting researchers from the international primatology community. The longitudinal individual-recognition database continues to be extended through ongoing monitoring of the population. The 2017 Schofield et al. cumulative culture reanalysis has, across the nine years since publication, become the canonical reference case for the cumulative-culture debate in non-human primates. And the cumulative research record that the contemporary biological literature has assembled across the 77 years of continuous Koshima research has, in 2026, established the population as the foundational empirical case in the comparative-cognition framework for cultural transmission in a non-human animal species.
The structural questions that the next several years of Koshima research will be addressing include whether the cumulative-culture reanalysis that the Schofield et al. 2017 paper articulated can be empirically validated through additional quantitative analyses of the multi-decade behavioral record, whether the contemporary population’s social-cognitive infrastructure continues to support the kind of behavioral innovation that produced the original 1953 sweet potato washing event, whether the climate-driven changes in the broader Miyazaki Prefecture environment will produce ecological pressures on the population that alter the cultural-transmission dynamics — paralleling the climate-driven habitat-shift pressures documented across other temperate-and-tropical wildlife populations facing convergent ecological stress — whether the broader comparative-cognition framework that has positioned the Japanese macaque alongside the chimpanzee, the orangutan, the capuchin, and the broader set of cultural-primate species can be extended to additional behavioral domains beyond those that the current research literature has addressed, and whether the contemporary population-level demographic and behavioral monitoring through the Koshima Field Station can be sustained across the multi-decade timescales required to characterize cultural transmission in the species’ long-lived multi-generational social structure.
The juvenile female carried the sweet potato to the stream. She washed the sand off. She ate the clean potato. Her mother watched. Her playmates watched. Her siblings watched. The behavior spread through the troop along kinship lines and playmate networks. The behavior persisted across multiple generations. The behavior elaborated through cumulative cultural modification across the multi-decade transmission record. The Kyoto University primatology school documented the entire process across more than seven decades of continuous observation. The contemporary comparative-cognition research community continues to draw on the Koshima record as the canonical reference case for cultural transmission in a non-human animal species. And the cumulative significance of the 1953 observation of a single juvenile Japanese macaque washing a single sweet potato in a single freshwater stream on a single Japanese islet has, across the subsequent 73 years of comparative-cognition research, progressively transformed the contemporary scientific understanding of what culture is, where it occurs in the animal kingdom, and what cognitive substrates support its emergence and maintenance across multi-generational timescales in non-human species — making the Koshima macaques of 2026 the empirical ground zero from which the entire contemporary animal-culture research framework has progressively developed across the past three-quarters of a century of continuous research operation at the Wildlife Research Center of Kyoto University’s Koshima Field Station on the small islet off the coast of Miyazaki Prefecture in southern Kyushu where Imo, in September 1953, first carried a sandy sweet potato to a stream and changed everything.