Charged 2026

Author: Joyce Ma

  • War of the Apes: Chimpanzee Civil War and the Evolution of Conflict

    Conflict and civil war have been an ever-constant presence in humanity, but they are not uniquely human phenomena. For the first time, researchers have described in detail the way that a chimpanzee group fissioned—or split—into two groups. Notably, the members of one group then began to violently attack the other group, killing chimpanzees that had been their groupmates only a few years ago.

    Some background: conflict and warfare in animals

    Human warfare is driven by a variety of factors, including our ability to readily develop cultural groups that then form strong ingroup attachments and outgroup hostility (Efferson et al., 2008). In other words, we readily form groups and show favoritism towards people who we consider to be also in the same group, while we are much less favorable towards people who we view as not in the group. Cultural differences can then become a driver of conflict.

    However, culture—language, social norms, ethnicity, religion, ideology, etc.—are distinctively human concepts. Nonhuman animals that also live in social groups, such as lions and wolves, can also have lethal, humanlike “wars” over issues like territory (Mosser & Packer, 2009; Cubaynes et al., 2014). Such animals notably do not have cultural markers in the same way humans do, and their conflicts are definitively driven by other factors, which can provide some insight into how group conflicts have evolved.

    But what about conflict that emerges from within a group? Somehow, ingroup morphs into outgroup. This happens in humans, but social animals can also experience permanent divisions in their groups, where the original group splinters into two distinct groups. Those divisions often occur mainly because of environmental reasons, such as competition over food, and the two groups formed after the split typically do not attack and kill each other (Sandel et al., 2026).

    One notable exception to this is a group of chimpanzees at Gombe, Tanzania, which permanently split into two groups in the 1970s. Males from one group, over the course of four years, killed all six males and one female in the other group. This is exceedingly rare—estimated to only occur roughly once every 500 years—and exactly how and why it happened is unclear: researchers at the time provided food to the chimpanzees, and certain details of the split are unclear due to their limited observations of the primates (Langergraber et al., 2014; Sandel et al., 2026).

    Chimp civil war

    Chimpanzees (Pan troglodytes), along with bonobos (Pan paniscus), are the closest animal relatives we humans have. Chimpanzees live in social groups, with males staying in the same social group for their entire lives, occasionally venturing out to attack other groups and expand their own territory (Mitani et al., 2010). Male chimpanzees mainly attack and kill male chimpanzees in other groups, but lethal violence can also erupt between chimpanzees in the same group, as seen with the Gombe group (Wilson et al., 2014). As such, studying their social behaviors may lend insight into our own.

    In their study published in 2026, Aaron Sandel and colleagues analyzed data from a group of over 200 chimpanzees, known as the Ngogo chimpanzees, in Kibale National Park, Uganda. Starting from 1998, the researchers tracked the movements of the Ngogo chimpanzees by recording the interactions the of the adult male chimpanzees of the group. Initially, from 1998 until 2014, the Ngogo chimpanzees were one cohesive group, with chimpanzees living, patrolling, feeding, and mating together. Subgroups of the main group existed, with a Western cluster and a Central cluster, but on average every year, almost a third of the chimpanzees would switch between the clusters, and almost half the infants conceived were by chimpanzees from different clusters.

    But this began to change in 2015, which would be the first sign of the fission of the Ngogo group. The group suddenly began to polarize. Chimpanzees in the Western cluster interacted more with each other and less with chimpanzees in the Central cluster, and vice versa. The clusters also increasingly stayed in only their region of the territory and began actively avoiding each other. After this year, infants were also only conceived by males and females in the same group.

    In 2016, the two clusters began to patrol their own territories, guarding against the other group, and in 2017, the two groups had increasingly hostile and violent encounters. In 2018, Ngogo chimpanzees permanently split into two groups, the Western group and the Central group.

    After this fission, despite consisting of less individuals, the Western group would regularly perform territorial patrols into the Central group’s territory, killing at least six adult males. In 2021, the Western group also started attacking infants, killing at least 14.

    It’s worth mentioning again that only a few years ago, these chimpanzees were all members of one cohesive group. This is emphasized in this one example highlighted by the researchers. In 2015, a group of Ngogo males, including three future Western males and one future Central male, patrolled together and showed friendly social interactions, such as embracing each other for reassurance. In 2019, a group of Western males, including the same three males, attacked and killed the Central male that they patrolled with less than 4 years prior.

    Why did this happen?

    The researchers proposed a few reasons why this fission happened.

    First, the original Ngogo group consisted of almost 200 individuals, and many males. With this large group, maintaining relationships with all the other chimpanzees in the group is impossible, and the large number of males in the group (30) meant that there was increased competition between the male chimpanzees.

    Additionally, a new alpha male rose to power in the group in 2015, at the same time the group began to polarize. Although both the previous alpha male and the new alpha male were part of the Central group, this change could have increased the instability and tension of the group.

    Lastly, the split may have been caused in part by deaths of certain chimpanzees who acted as important nodes in the network of relationships in the group. The deaths of those chimps may have weakened relationships across the group and facilitated the fission. For example, in 2014, just before the beginning of the polarization, five adult males and one adult female died. In 2017, as the group was already beginning to divide, 25 chimpanzees in the group died in an epidemic, including an adult male that was one of the last individuals that connected the two groups. The deaths of these individuals could have weakened the relationships between the two clusters, effectively helping cleave the original Ngogo group into the Central and Western group.

    What does this mean?

    According to the researchers, this violence is notable because it shows us how aggression and group identity forms in chimpanzees and how group conflicts develop in the absence of cultural factors.

    Typically, as male chimpanzees stay in the same group their entire lives, they behave aggressively towards strangers. However, as the attacks described were towards chimpanzees they already knew, it shows that group identity in chimpanzees can be flexible and is controlled by other factors, beyond just familiarity.

    This study also describes how relationship dynamics can play a major role in group conflicts. Although not to the scale of human wars, this “civil war” between the Ngogo chimpanzees shows how a major group conflict can stem from the dissolution of relationships between individuals. If the right (or rather wrong) relationships are broken, the unity of a group may also soon be in jeopardy, even without cultural factors like ethnicity and religion.

    The fission of the Ngogo chimpanzees can feel like an omen of our future as humans, forever violent and marked by splintering factions. But it’s worth remembering that we humans are capable of violence but also of empathy. Even comparatively violent, conflict-prone chimpanzees show empathetic actions. Chimpanzee bystanders of a fight will go to comfort the losing chimp afterwards, and chimps can also show reconciliatory behaviors after a fight, such as holding hands, embracing, or kissing (De Waal, 2012; De Waal, 2000).

    As James Brooks notes in his 2026 perspective article on the study, we can also turn to look at our other, equally close great ape relative, the bonobo. Once thought to be a subspecies of chimpanzees, bonobos are much more peaceful: even though bonobos live in social groups, the groups do not violently interact. Bonobos not only form cooperative relationships within their own groups but also with individuals from other groups (Samuni & Surbeck, 2023). Lastly, even though bonobo groups can permanently split, it doesn’t result in the violence seen in the Ngogo fission. A group of bonobos in Wamba, Democratic Republic of the Congo permanently split almost 50 years ago, but continue to peacefully coexist (Brooks, 2026; Kuroda, 2023).

    Overall, this study shows that conflict emerges even in the absence of cultural markers—instead, a key factor of group conflict might lie in the way social relationships form, are maintained, and break down. As such, this can also be reversed, as those basic social processes might also be a way to approach conflict resolution. By better understanding the way in which a group splits into warring factions, we can also make headway into understanding how to prevent and resolve such instances from occurring in ourselves.

    Indeed, as the researchers state in the closing of their paper, “it may be in the small, daily acts of reconciliation and reunion between individuals that we find opportunities for peace.”

    Writing by Joyce Ma

    Picture by © Giles Laurent, gileslaurent.com, License CC BY-SA, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=134376811

     

    References

    Brooks, J. (2026). Civil war among wild chimpanzees. Science, 392(6794), 146–147. https://doi.org/10.1126/science.aeg6719

    Cubaynes, S., MacNulty, D. R., Stahler, D. R., Quimby, K. A., Smith, D. W., & Coulson, T. (2014). Density‐dependent intraspecific aggression regulates survival in northern Yellowstone wolves (Canis lupus). Journal of Animal Ecology, 83(6), 1344–1356. https://doi.org/10.1111/1365-2656.12238

    De Waal, F. B. M. (2000). Primates–A natural heritage of conflict resolution. Science, 289(5479), 586–590. https://doi.org/10.1126/science.289.5479.586

    De Waal, F. B. M. (2012). The antiquity of empathy. Science, 336(6083), 874–876. https://doi.org/10.1126/science.1220999

    Efferson, C., Lalive, R., & Fehr, E. (2008). The coevolution of cultural groups and ingroup favoritism. Science, 321(5897), 1844–1849. https://doi.org/10.1126/science.1155805

    Kuroda, S. (2023). From the Early Days of Bonobo Research. In Bonobos and People at Wamba: 50 Years of Research (pp. 25–37). https://doi.org/10.1007/978-981-99-4788-1_2

    Langergraber, K. E., Rowney, C., Schubert, G., Crockford, C., Hobaiter, C., Wittig, R., Wrangham, R. W., Zuberbühler, K., & Vigilant, L. (2014). How old are chimpanzee communities? Time to the most recent common ancestor of the Y-chromosome in highly patrilocal societies. Journal of Human Evolution, 69, 1–7. https://doi.org/10.1016/j.jhevol.2013.12.005

    Mitani, J. C., Watts, D. P., & Amsler, S. J. (2010). Lethal intergroup aggression leads to territorial expansion in wild chimpanzees. Current Biology, 20(12), R507–R508. https://doi.org/10.1016/j.cub.2010.04.021

    Mosser, A., & Packer, C. (2009). Group territoriality and the benefits of sociality in the African lion, Panthera leo. Animal Behaviour, 78(2), 359–370. https://doi.org/10.1016/j.anbehav.2009.04.024

    Samuni, L., & Surbeck, M. (2023). Cooperation across social borders in bonobos. Science, 382(6672), 805–809. https://doi.org/10.1126/science.adg0844

    Sandel, A. A., He, Y., Ren, J., Kei, Y. L., Lee, K. C., Clark, I. R., Reddy, R. B., Negrey, J. D., Birungi, C., Apamaku, B. A., Kanweri, D., Kalunga, D., Aliganyira, C., Ramírez-Amaya, S., Nakayima, P., Katumba, R., Kamugyisha, B., Acosta-Florez, D., Van Boekholt, B., . . . Mitani, J. C. (2026). Lethal conflict after group fission in wild chimpanzees. Science, 392(6794), 216–220. https://doi.org/10.1126/science.adz4944

    Wilson, M. L., Boesch, C., Fruth, B., Furuichi, T., Gilby, I. C., Hashimoto, C., Hobaiter, C. L., Hohmann, G., Itoh, N., Koops, K., Lloyd, J. N., Matsuzawa, T., Mitani, J. C., Mjungu, D. C., Morgan, D., Muller, M. N., Mundry, R., Nakamura, M., Pruetz, J., . . . Wrangham, R. W. (2014). Lethal aggression in Pan is better explained by adaptive strategies than human impacts. Nature, 513(7518), 414–417. https://doi.org/10.1038/nature13727

  • Bouba? Kiki? Baby Chicks Associate Sounds With Shapes

    One of the chicks above is named “Bouba.” The other is named “Kiki.” Going just off of your gut intuition, which one is which?

    If you answered that the left chick is “Bouba” and the right chick is “Kiki”, many people agree with you, including speakers of over 25 languages, belonging to 9 language families and 11 writings systems—a surprisingly high number, given that these are purely nonsense words (Ćwiek et al., 2021). For some reason, “bouba” is obviously round, while “kiki” is obviously spiky.

    Perhaps even more astonishing is that, as discovered in a recent study by Maria Loconsole and colleagues at the University of Padova, baby chickens are among the population that agrees with you.

    What is the bouba-kiki effect?

    Most words have an arbitrary relationship to their meaning. Nothing about “cat” inherently refers to the feline domestic animal, and neither does 猫 (māo), बिल्ली (billi), gato, or قطة (qiṭṭa). But certain sounds seem to inherently have meaning.

    First described in 1947 by Wolfgang Kölher through the nonsense words “Maluma” and “Takete”, the “bouba-kiki” phenomenon in linguistics refers to this effect (Loconsole et al., 2026). “Maluma” and “bouba” feel inherently round, while “takete” and “kiki” feel inherently sharp and spiky. This effect is common across cultures, languages, and age: even infants as young as 4 months possess this sound mapping, where certain sounds seem to inherently correspond to certain shapes (Ozturk et al., 2013). This effect is even found (to a lesser extent) in blind individuals, though a period of sight seems necessary for the effect to occur (Piller et al., 2023).

    The most common explanation for the bouba-kiki effect is the way we say those syllables. When we say “bouba” and similar words, our mouths make a round shape; when we say “kiki” and similar words, our mouths make an angular shape. Our brains thus associate words that are “round” to pronounce with round shapes, and “angular” with angular shapes. Alternatively, the shape of the letters “b” and “o” are round, while the shape of the letters “k” and “i” are angular (Lockwood & Dingemanse, 2015).

    However, this hypothesis is challenged by the generic shape hypothesis, which states that humans form generic associations between certain sounds and meanings. This hypothesis was proposed in a study conducted by Ananya Passi and S. P. Arun in 2019, where the bouba-kiki effect was found with unpronounceable words, and an association was even found between clear tones and shape, where higher tones were associated with angular shapes. This indicates that humans potentially form general associations between sounds and shapes, regardless of the way those sounds can be pronounced. However, the reason why those associations might be formed remains unanswered, and these studies have been restricted to humans.

    Other animals have been shown to also experience some form of association between sound and another sense: for example, chimpanzees, tortoises, and dogs associate lower pitches with larger objects and higher pitches with smaller objects (Kalan et al., 2014; Korzeniowska et al., 2022; Loconsole et al., 2023). However, the bouba-kiki effect specifically has not been found to exist in other animals, even great apes, such as chimpanzees and a bonobo (Margiotoudi et al., 2019; Margiotoudi et al., 2022).

    Baby chicks?

    If the effect isn’t even found in our closest animal relatives, then where else can researchers look? In 2026, Loconsole and her colleagues decided to change tracks and look elsewhere. As surprising as their choice may seem, their pick of animals wasn’t arbitrary: chickens are precocial creatures, which means that they can be tested shortly after hatching, and chicks also share many cognitive mechanisms with human infants (Wood & Wood, 2021).

    In the first part of the study conducted by Loconsole and her colleagues, 3-day-old chicks were trained to go around a panel depicting a shape with both spiky and round edges, with food behind the panel acting as an incentive. During the experiment, the chicks were placed in front of two panels. One of the panels displayed a round shape, and the other one displayed a spiky shape, and neither of the panels concealed food. The researchers played a recording of a human voice saying either “bouba” or “kiki” to the enclosure, and they watched to see which panel the chicks would choose.

    In the second part of the experiment, 1-day-old chicks were introduced to an enclosure with a screen that once again showed a shape with both spiky and round edges, though there was no incentive. After the chicks grew accustomed to the screen, the researchers changed it up: like the first part of the experiment, the screen now showed two shapes side by side, with one jagged shape and one blobby shape. The researchers once again played either “bouba” or “kiki”, and they recorded which shape the chicks approached first, as well as which shape they spent more time exploring.

    The researchers found that the 3-day-old chicks significantly preferred the panel with the round shape when hearing “bouba”, and the panel with the angular shape when hearing “kiki”. They also found the same results with the 1-day-old chicks: when “bouba” was played, the chicks first approached the round shape significantly more and spent more time exploring the round shape. The reverse was true when “kiki” was played.

    What does this mean?

    The study shows that this bouba-kiki effect is not learned, but rather something inherent that’s present even in the earliest stages of life. One implication of this study is that this crossmodal association, or association between different senses, plays a role in how communication develops between animals. Animals such as chickens do not have language, but they still communicate through various calls and vocalizations. Although these vocalizations aren’t necessarily directly symbolic, having these innate associations may help with future development of more complex communication.

    Additionally, the findings of the study indicate that the bouba-kiki effect isn’t specific to humans or even mammals, but rather throughout all vertebrates. But how does this reconcile with past findings wherein the effect was not found in other great apes? After all, it’s rather unlikely that this association evolved separately in birds and in humans, but skipped our closest great ape relatives.

    According to Loconsole and colleagues, this difference may be explained by the difference in methodology between experiments, as well as the past experience and training of the research subjects. Kanzi, the bonobo who was tested for the bouba-kiki effect, was already trained in associating sounds and shapes and was capable of correctly matching English words to pictures, which may have played a role in his choices (Loconsole et al., 2026; Margiotoudi et al., 2022).

    So what do the findings of the study mean for the bouba-kiki effect and the development of human language? Does this mean that chickens are also capable of speech?

    No, not really. The bouba-kiki effect is only one example of the human ability of iconicity, or the capacity to form associations between form and meaning, argue Marcus Perlman and Bodo Winter in their commentary article in response to the 2026 study. In other words, the study reveals that the effect originates further back in the tree of life, but the origins of language lie elsewhere, in a broader framework. The bouba-kiki effect may reflect one way in which human language developed through associations between senses, but humans are able to form much more complex associations in language through a combination of speech, gestures, and visual signs. As such, researchers must look at other, broader areas for more clues in their hunt for the origins of language (Perlman & Winter, 2026).

    So overall, the chicks might agree with your naming of their illustrated compatriots, but unfortunately, they won’t be able to say as much in words.

    Want to learn more about the bouba-kiki effect? Check out our past article on the phenomenon!

    Writing and illustration by Joyce Ma

     

    References

    Ćwiek, A., Fuchs, S., Draxler, C., Asu, E. L., Dediu, D., Hiovain, K., Kawahara, S., Koutalidis, S., Krifka, M., Lippus, P., Lupyan, G., Oh, G. E., Paul, J., Petrone, C., Ridouane, R., Reiter, S., Schümchen, N., Szalontai, Á., Ünal-Logacev, Ö., Zeller, J., Perlman, M., Winter, B. (2021). The bouba/kiki effect is robust across cultures and writing systems. Philosophical Transactions of the Royal Society B Biological Sciences, 377(1841), 20200390. https://doi.org/10.1098/rstb.2020.0390

    Kalan, A. K., Mundry, R., & Boesch, C. (2015). Wild chimpanzees modify food call structure with respect to tree size for a particular fruit species. Animal Behaviour, 101, 1–9. https://doi.org/10.1016/j.anbehav.2014.12.011

    Korzeniowska, A. T., Simner, J., Root-Gutteridge, H., & Reby, D. (2022). High-pitch sounds small for domestic dogs: Abstract crossmodal correspondences between auditory pitch and visual size. Royal Society Open Science, 9(2), 211647. https://doi.org/10.1098/rsos.211647

    Lockwood, G., & Dingemanse, M. (2015). Iconicity in the lab: A review of behavioral, developmental, and neuroimaging research into sound-symbolism. Frontiers in Psychology, 6, 1246. https://doi.org/10.3389/fpsyg.2015.01246

    Loconsole, M., Benavides-Varela, S., & Regolin, L. (2026). Matching sounds to shapes: Evidence of the bouba-kiki effect in naïve baby chicks. Science, 391(6787), 836–839. https://doi.org/10.1126/science.adq7188

    Loconsole, M., Stancher, G., & Versace, E. (2023). Crossmodal association between visual and acoustic cues in a tortoise (Testudo hermanni). Biology Letters, 19(7), 20230265. https://doi.org/10.1098/rsbl.2023.0265

    Margiotoudi, K., Allritz, M., Bohn, M., & Pulvermüller, F. (2019). Sound symbolic congruency detection in humans but not in great apes. Scientific Reports, 9(1), 12705. https://doi.org/10.1038/s41598-019-49101-4

    Margiotoudi, K., Bohn, M., Schwob, N., Taglialatela, J., Pulvermüller, F., Epping, A., Schweller, K., & Allritz, M. (2022). Bo-NO-bouba-kiki: Picture-word mapping but no spontaneous sound symbolic speech-shape mapping in a language trained bonobo. Proceedings of the Royal Society B Biological Sciences, 289(1968), 20211717. https://doi.org/10.1098/rspb.2021.1717

    Ozturk, O., Krehm, M., & Vouloumanos, A. (2012). Sound symbolism in infancy: Evidence for sound–shape cross-modal correspondences in 4-month-olds. Journal of Experimental Child Psychology, 114(2), 173–186. https://doi.org/10.1016/j.jecp.2012.05.004

    Passi, A., & Arun, S. P. (2022). The Bouba–Kiki effect is predicted by sound properties but not speech properties. Attention Perception & Psychophysics, 86(3), 976–990. https://doi.org/10.3758/s13414-022-02619-8

    Perlman, M., & Winter, B. (2026). In search of meaning. Science, 391(6787), 762–763. https://doi.org/10.1126/science.aee8641

    Piller, S., Senna, I., & Ernst, M. O. (2023). Visual experience shapes the Bouba-Kiki effect and the size-weight illusion upon sight restoration from congenital blindness. Scientific Reports, 13(1), 11435. https://doi.org/10.1038/s41598-023-38486-y

    Wood, S. M. W., & Wood, J. N. (2021). One-shot object parsing in newborn chicks. Journal of Experimental Psychology General, 150(11), 2408–2420. https://doi.org/10.1037/xge0001043