Comparative rates of violence in chimpanzees and humans (original) (raw)
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Primates, 2023
aggression is a familiar component of the behavioural repertoire of many forest-dwelling chimpanzee (Pan troglodytes) communities. However, until now, the absence of intercommunity attacks -including killings -in communities that live in open, mosaic environments has supported hypotheses of reduced resource competition in drier habitats, and informed referential models of early hominin social dynamics in a similar habitat. In June 2020, we observed the first instance of intercommunity lethal aggression, a male-committed infanticide, by the Issa chimpanzee community, which live in a savannah-mosaic habitat in the Issa Valley, western Tanzania. The carcass was recovered by researchers after it was abandoned by the attackers. Here, we give a detailed account of the events leading up to and including the infanticide, and contextualise our observations with what has been described for other chimpanzee communities. Notably, in contrast to the majority of reported intercommunity infanticides, the infant male victim was castrated (and not cannibalised), making this the youngest reported castration. This observation of intercommunity aggression disproves its hypothesised absence in savannah-dwelling chimpanzees, which by extension, has implications for early hominin evolution. We suggest that the near absence of observations of intercommunity aggression in savannah chimpanzee communities is most likely due to the lack of long-term study communities, and in some cases geographic isolation. We hypothesise that food-rich areas within a habitat with otherwise widely distributed food sources may select for intense intercommunity aggression despite the low population density characteristic of savannah communities. Anecdotes such as this add to the comparative database available on intercommunity killings in chimpanzee society, improving our ability to draw inferences about their evolutionary significance.
American Journal of Primatology, 2008
Intercommunity aggression in chimpanzees and primitive warfare in humans possess striking similarities, such as the common occurrence of large male coalitions, systematic control of territory boundaries, and lethal attacks on isolated individuals from neighboring groups. However, an important apparent contrast is the absence of recurrent peaceful interactions between neighboring groups of chimpanzees. We observed a remarkable range of behavior in intergroup encounters among three habituated communities of chimpanzees in Taï National Park, Côte d'Ivoire. Lethal attacks are documented in these study groups for the first time, as well as year-long exchanges of parous adult females and peaceful intergroup visits of mothers with infants. Demographic factors, including group size and number of adult males, are shown to affect the nature of intergroup interactions in ways not considered previously. A reconsideration of the difference in intergroup interactions between eastern and western chimpanzees is proposed including a more important consideration of the female's perspective. The inclusion of the new complexities in intergroup interactions in chimpanzees allows new parallels to be drawn with the evolution of primitive warfare in humans. Am.
International Journal of Primatology, 2017
Lethal coalitionary aggression is of significant interest to primatologists and anthropologists given its pervasiveness in human, but not nonhuman, animal societies. Chimpanzees (Pan troglodytes) provide the largest sample of recorded lethal coalitionary aggression in nonhuman primates, and most long-term chimpanzee study sites have recorded coalitionary killing of conspecifics. We report an inferred lethal attack by resident males on a former alpha male chimpanzee (P. t. verus) at Fongoli in Senegal. We describe the male's presence in the Int J Primatol
American Journal of Primatology, 2013
Chimpanzees (Pan troglodytes) are capable of extreme violence. They engage in inter-group, sometimes lethal, aggression that provides the winners with an opportunity to enlarge their territory, increase their food supply and, potentially, attract more mates. Lethal violence between adult males also occurs within groups but this is rare; to date, only four cases (three observed and one inferred) have been recorded despite decades of observation. In consequence, the reasons for within-group lethal violence in chimpanzees remain unclear. Such aggression may be rare due to the importance of coalitions between males during inter-group encounters; cooperation between males is also thought to be key in the defense or advancement of social rank within the group. Previous accounts of within-group lethal violence concern victims who were low-ranking males; here we provide the first account of the killing of an incumbent alpha male by a coalition of adult males from the same community. We found no clear evidence that the alpha male’s position was under threat during the months before the lethal attack: the male dominance hierarchy was highly stable, with low rates of male-male aggression, and there were no significant changes in social interactions (i.e. grooming and aggression) between the alpha male and the other adult males. Two of the four attackers were former alpha males and were the individuals with whom the victim appeared, in the period preceding his death, to be most strongly affiliated: his most frequent grooming partners and those with whom he spent most time in proximity. The lethal attack triggered a period of instability in the male hierarchy and was likely an opportunistic attempt to seize alpha status by the third-ranking male.
Lethal aggression in Pan is better explained by adaptive strategies than human impacts
Nature 513: 414-419, 2014
Observations of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) provide valuable comparative data for understanding the significance of conspecific killing. Two kinds of hypothesis have been proposed. Lethal violence is sometimes concluded to be the result of adaptive strategies, such that killers ultimately gain fitness benefits by increasing their access to resources such as food or mates 1-5 . Alternatively, it could be a non-adaptive result of human impacts, such as habitat change or food provisioning 6-9 . To discriminate between these hypotheses we compiled information from 18 chimpanzee communities and 4 bonobo communities studied over five decades. Our data include 152 killings (n 5 58 observed, 41 inferred, and 53 suspected killings) by chimpanzees in 15 communities and one suspected killing by bonobos. We found that males were the most frequent attackers (92% of participants) and victims (73%); most killings (66%) involved intercommunity attacks; and attackers greatly outnumbered their victims (median 8:1 ratio). Variation in killing rates was unrelated to measures of human impacts. Our results are compatible with previously proposed adaptive explanations for killing by chimpanzees, whereas the human impact hypothesis is not supported.
Are great apes aggressive? A cross‑species comparison
2006
csousa@fcsh.uml.pt Abstract This paper aims to characterise the aggressive behaviour of great apes: the orang‑utan, the gorilla, the chimpanzee and the bonobo. We start by discussing the lack of consensual definitions for terms such as violence, aggression and ago ‑ nistic behaviour. Secondly, we describe the evidence of aggression in each species. Finally we describe several referential models developed to explain the way of life and aggressive behaviour of the first hominins through insights provided from the behaviour of non‑human primates.
Primate aggression and evolution: an overview of sociobiological and anthropological perspectives
The Bulletin of the American Academy of Psychiatry and the Law, 1983
Attempts to explain the nature and causes of human aggression are handicapped primarily because aggression is anything but a unitary concept. Aggression has no single etiology, no matter which mammalian species we consider or what kind of causation (developmental or evolutionary) we stress. Nevertheless, forensic psychiatrists are asked to evaluate instances of human aggression in ways that would send shivers up the spines of researchers who have been wrestling with the issue for over fifty years. This is not to say forensic psychiatry should be abolished nor to suggest behavioral scientists have not made progress in discovering causes of species aggression in genera}l and human violence in particular. 2 But especially when predictive models are considered it does mean we are far from achieving highly reliable results.: l Particularly when one person is asked to assess the motivational state of another who has committed a serious aggressive act it becomes more evident just how much more data we need. Strangely, if a forensic psychiatrist were asked to testify in a case in which, let us say, one monkey attacked another, the testimony would be based on more complete information than a case involving a human. This is because a plethora of context-specific data on nonhuman primates are available. These data illuminate a wide range of social, ecological, and endocrinological circumstances under which animals will be expected to act aggressively. Data on humans are much more complex, and sometimes they are absent altogether. For obvious ethical reasons scientists do not purposefully nor directly experiment on humans (biochemically, surgically, or hormonally) to determine how and when aggression can be induced. Moreover, among humans culture and biology are so tightly wedded that the task of identifying and isolating the. most salient aggression-eliciting factors is formidable, if, indeed, there is such a thing. If this is not discouraging enough, consider that the data available on human aggression, especially motivation, often lead in diverse directions without any indications about which direction may be most fruitful to explore. 4 Perhaps I have painted an overly pessimistic picture. Just as forensic psychiatrists analyze and present conclusions about the mental states of accused aggressors, so also do researchers make use of a wide range of principles and assumptions in putting forth their hypotheses on primate
This paper aims to characterise the aggressive behaviour of great apes: the orang‑utan, the gorilla, the chimpanzee and the bonobo. We start by discussing the lack of consensual definitions for terms such as violence, aggression and ago‑ nistic behaviour. Secondly, we describe the evidence of aggression in each species. Finally we describe several referential models developed to explain the way of life and aggressive behaviour of the first hominins through insights provided from the behaviour of non‑human primates.
Primates, 2003
During 12 years of observation, we have observed three confirmed and two inferred lethal coalitionary attacks on adult male white-faced capuchins (Cebus capucinus) by members of two habituated social groups at Lomas Barbudal Biological Reserve, Costa Rica. In one case, an alpha male was badly wounded and evicted from his group, and when later found by his former groupmates he was attacked by several of them and died less than 24 h later. In two other cases, lone extra-group males were mobbed by adult and immature males of a bisexual group. One victim's abdomen was torn open and he died less than 24 h later. A second victim was quite badly bitten but may have escaped. The fourth and fifth cases resulted from intergroup encounters. One victim lost the use of both arms but may have survived, whereas the other died of unknown causes within an hour of the attack. The observed death rate from coalitionary aggression at our site is approximately the same as that reported for eastern chimpanzees. Because at least three of the five observed incidents involved large coalitions attacking lone victims, they support the general hypothesis that imbalances of power contribute to intraspecific killing in primates. However, the occurrence of lethal coalitional attacks in a species lacking fission-fusion social organization poses a challenge to the more specific version of the imbalance-of-power hypothesis proposed by Manson and Wrangham in 1991 to explain chimpanzee and human intergroup aggression.
Scientific Reports
Intraspecies violence, including lethal interactions, is a relatively common phenomenon in mammals. Contrarily, interspecies violence has mainly been investigated in the context of predation and received most research attention in carnivores. Here, we provide the first information of two lethal coalitionary attacks of chimpanzees (Pan troglodytes troglodytes) on another hominid species, western lowland gorillas (Gorilla gorilla gorilla), that occur sympatrically in the Loango National Park in Gabon. In both events, the chimpanzees significantly outnumbered the gorillas and victims were infant gorillas. We discuss these observations in light of the two most widely accepted theoretical explanations for interspecific lethal violence, predation and competition, and combinations of the two-intraguild predation and interspecific killing. Given these events meet conditions proposed to trigger coalitional killing of neighbours in chimpanzees, we also discuss them in light of chimpanzees’ in...
American Journal of Primatology, 2002
We document here an unusual case of intense aggression against an infant male from another group by chimpanzees (Pan troglodytes schweinfurthii) of the Mahale Mountains National Park, in Tanzania. Adult males of the study group collectively attacked an unknown male infant. Although an unknown female, probably the mother, tried to retrieve him, the infant was seriously injured and most likely died. During this incident, the unknown female attacked and injured two researchers. After the aggressive encounter, it was found that six of the nine adult males in the study group were wounded. Attacking the extragroup male infant may have the effect of weakening the future power of the neighboring group, leading to better access to resources and enhanced safety in the future for the study group. Am.
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Genetic differentiation and the evolution of cooperation in chimpanzees and humans
Proceedings of the Royal Society B: Biological Sciences, 2011
It has been proposed that human cooperation is unique among animals for its scale and complexity, its altruistic nature and its occurrence among large groups of individuals that are not closely related or are even strangers. One potential solution to this puzzle is that the unique aspects of human cooperation evolved as a result of high levels of lethal competition (i.e. warfare) between genetically differentiated groups. Although between-group migration would seem to make this scenario unlikely, the plausibility of the between-group competition model has recently been supported by analyses using estimates of genetic differentiation derived from contemporary human groups hypothesized to be representative of those that existed during the time period when human cooperation evolved. Here, we examine levels of between-group genetic differentiation in a large sample of contemporary human groups selected to overcome some of the problems with earlier estimates, and compare them with those of chimpanzees. We find that our estimates of between-group genetic differentiation in contemporary humans are lower than those used in previous tests, and not higher than those of chimpanzees. Because levels of between-group competition in contemporary humans and chimpanzees are also similar, these findings suggest that the identification of other factors that differ between chimpanzees and humans may be needed to provide a compelling explanation of why humans, but not chimpanzees, display the unique features of human cooperation.
Primates, 2009
Primate socioecological studies have attempted to derive general frameworks using the average behavioural traits of species or genera to place them into categories. However, with the accumulation of primate studies, it is timely to place more emphasis on understanding within-species variation in social structure. In this review we have four objectives. First, we examine within-species variation in the potential determinants of social structure, including diet, demography, predation and infanticide, and document considerable variation. Second, we present case studies of within-species variation in social structure to illustrate the potential magnitude of this variation. For example, there are cases within a single interbreeding population where multi-male, uni-male, fission–fusion and monogamous groups are found. Third, by examining widespread primate lineages that occur in a variety of habitats, we note that there are differences in the magnitude of variation in social structures across different lineages and as a result we consider phylogenetic constraints on phenotypic variation in social structure. Finally, we reflect on the implications of extensive variation in social structure. We suggest that primate social structure will represent a combination of adaptation to present-day environment and phylogenetic inertia. To advance our understanding of the relative contribution of phylogeny versus ecology we propose two approaches. One approach is to compare groups in the same interbreeding population that inhabit different ecological conditions. Any differences that are found can be attributed to ecological differences, since phylogeny should not play a role within a single population. The second approach is to study distantly related species that have similar social structures to illustrate how similar ecological pressures might be operating to select for parallel social structures.
Domestication Alone Does Not Lead to Inequality
Current Anthropology, 2010
We present empirical measures of wealth inequality and its intergenerational transmission among four horticulturalist populations. Wealth is construed broadly as embodied somatic and neural capital, including body size, fertility and cultural knowledge, material capital such as land and household wealth, and relational capital in the form of coalitional support and field labor. Wealth inequality is moderate for most forms of wealth, and intergenerational wealth transmission is low for material resources and moderate for embodied and ...
Politics and the Life Sciences, 2007
Johan MG van der DennenPh.D. ... Keith F. Otterbein, How War Began (College Station: Texas A&M Press, 2004), xv + 292 pages. ISBN:1-58544-330-1. ... Douglas P. Fry, The Human Potential for Peace: An anthropological challenge to assumptions about war and violence (New ...
Infanticide in chimpanzees: Taphonomic case studies from Gombe
American journal of physical anthropology, 2017
We present a study of skeletal damage to four chimpanzee (Pan troglodytes) infanticide victims from Gombe National Park, Tanzania. Skeletal analysis may provide insight into the adaptive significance of infanticide by examining whether nutritional benefits sufficiently explain infanticidal behavior. The nutritional hypothesis would be supported if bone survivorship rates and skeletal damage patterns are comparable to those of monkey prey. If not, other explanations, such as the resource competition hypothesis, should be considered. Taphonomic assessment of two chimpanzee infants included description of breakage and surface modification, data on MNE, %MNE, and bone survivorship. Two additional infants were assessed qualitatively. The data were compared to published information on monkey prey. We also undertook a review of published infanticide cases. The cases were intercommunity infanticides (one male and three female infants) committed by males. Attackers partially consumed two of ...
The emergence of human warfare: Current perspectives
American Journal of Physical Anthropology
The origins of warfare have long been of interest for researchers across disciplines. Did our earliest ancestors engage in forms of organized violence that are appropriately viewed as approximations, forms of, or analogs for more recent forms of warfare? Assessed in this article are contrasting views that see warfare as being either a product of more recent human societies or a phenomenon with a much deeper chronology. The article provides an overview of current debates, theories, and methodological approaches, citing literature and data from archaeological, ethnographic, genetic, primatological, and paleoanthropological studies. Synthetic anthropological treatments are needed, especially in efforts to inform debates among nonacademic audiences, because the discipline's approaches are ideally suited to study the origins of warfare. Emphasized is the need to consider possible forms of violence and intergroup aggression within Pleistocene contexts, despite the methodological challenges associated with fragmentary, equivocal, or scarce data. Finally, the review concludes with an argument about the implications of the currently available data. We propose that socially cooperative violence, or "emergent warfare," became possible with the onset of symbolic thought and complex cognition. Viewing emergent warfare as a byproduct of the human capacity for symbolic thought explains how the same capacities for communication and sociality allowed for elaborate peacemaking, conflict resolution, and avoidance. Cultural institutions around war and peace are both made possible by these changes. Accordingly, we suggest that studies on warfare's origins should be tied to research on the advent of cooperation, sociality, and communication.
Long-term repeatability in social behaviours suggests stable social phenotypes in wild chimpanzees
Animals living in social groups navigate challenges when competing and cooperating with other group members. Changes in demographics, dominance hierarchies or ecological factors, such as food availability or disease prevalence, are expected to influence decision-making processes regarding social interactions. Therefore, it could be expected individuals show flexibility in social behaviour over time to maximise the fitness benefits of social living. To date, research across species has shown that stable inter-individual differences in social behaviour exist, but mostly over relatively short data collection time periods. Using data spanning over 20 years, we demonstrate that multiple social behaviours are repeatable over the long-term in wild chimpanzees, a long-lived species occupying a complex fission-fusion society. We controlled for temporal, ecological and demographic changes, limiting pseudo-repeatability. We conclude that chimpanzees living in natural ecological settings have r...
The American Biology Teacher
Evolutionary anthropologists commonly describe humans as a highly cooperative species, based on our evolved socio-cognitive capacities. However, students and the general public may not necessarily share this view about our species. At the same time, fostering our ability to cooperate is considered a key foundation for achieving sustainable development, and students’ understanding of the conditions that enable or hinder cooperation is therefore an important learning goal in sustainability education. In this article, we describe a small classroom activity that explored students’ and preservice biology teachers’ preconceptions about the human capacity to cooperate around shared resources in comparison to the capacity of our closest relative, the chimpanzee. Results indicate that students and teachers had limited knowledge about the evolved human capacity for cooperation around shared resources in small groups, most often viewing chimpanzees as more capable of cooperation and sustainabl...
Zoo Biology, 2016
Chimpanzees in laboratory colonies experience more wounds on week days than on weekends, which has been attributed to the increased number of people present during the week; thus the presence of more people was interpreted as stressful. If this were also true for primates in zoos, where high human presence is a regular feature, this would clearly be of concern. Here we examine wounding rates in two primate species (chimpanzees Pan troglodytes and ring-tailed lemurs Lemur catta) at three different zoos, to determine whether they correlate with mean number of visitors to the zoo. Wounding data were obtained from zoo electronic record keeping system (ZIMS™). The pattern of wounds did not correlate with mean gate numbers for those days for either species in any group. We conclude that there is no evidence that high visitor numbers result in increased woundings in these two species when housed in zoos.
Politics and the Life Sciences
We tracked the relative integration and differentiation among life history traits over the period spanning AD 1800–1999 in the Britannic and Gallic biocultural groups. We found that Britannic populations tended toward greater strategic differentiation, while Gallic populations tended toward greater strategic integration. The dynamics of between-group competition between these two erstwhile rival biocultural groups were hypothesized as driving these processes. We constructed a latent factor that specifically sought to measure between-group competition and residualized it for the logarithmic effects of time. We found a significantly asymmetrical impact of between-group competition, where the between-group competition factor appeared to be driving the diachronic integration in Gallic populations but had no significantly corresponding influence on the parallel process of diachronic differentiation in Britannic populations. This suggests that the latter process was attributable to some a...
Language as a coordination tool evolves slowly
Royal Society Open Science, 2016
Social living ultimately depends on coordination between group members, and communication is necessary to make this possible. We suggest that this might have been the key selection pressure acting on the evolution of language in humans and use a behavioural coordination model to explore the impact of communication efficiency on social group coordination. We show that when language production is expensive but there is an individual benefit to the efficiency with which individuals coordinate their behaviour, the evolution of efficient communication is selected for. Contrary to some views of language evolution, the speed of evolution is necessarily slow because there is no advantage in some individuals evolving communication abilities that much exceed those of the community at large. However, once a threshold competence has been achieved, evolution of higher order language skills may indeed be precipitate.
Misrepresentations of Evolutionary Psychology in Sex and Gender Textbooks
Evolutionary Psychology, 2014
Evolutionary psychology has provoked controversy, especially when applied to human sex differences. We hypothesize that this is partly due to misunderstandings of evolutionary psychology that are perpetuated by undergraduate sex and gender textbooks. As an initial test of this hypothesis, we develop a catalog of eight types of errors and document their occurrence in 15 widely used sex and gender textbooks. Consistent with our hypothesis, of the 12 textbooks that discussed evolutionary psychology, all contained at least one error, and the median number of errors was five. The most common types of errors were “Straw Man,” “Biological Determinism,” and “Species Selection.” We conclude by suggesting improvements to undergraduate sex and gender textbooks.
Evolutionary Psychology, 2014
Adult humans are characterized by low rates of intra-group physical aggression. Since children tend to be more physically aggressive, an evolutionary developmental account shows promise for explaining how physical aggression is suppressed in adults. I argue that this is achieved partly through extended dominance hierarchies, based on indirect reciprocity and linguistic transmission of reputational information, mediated by indirectly aggressive competition. Reviewing the literature on indirect and related forms of aggression provides three pieces of evidence for the claim that evolutionarily old impulses towards physical aggression are socialized into indirect aggression in humans: (i) physical aggression falls in early childhood over the same age range at which indirect aggression increases; (ii) the same individuals engage in both direct and indirect aggression; and (iii) socially dominant individuals practice indirect aggression more frequently. Consideration of the developmental ...
Why male orangutans do not kill infants
Behavioral Ecology and Sociobiology, 2009
Infanticide is widespread among mammals, is particularly common in primates, and has been shown to be an adaptive male strategy under certain conditions. Although no infanticides in wild orangutans have been reported to date, several authors have suggested that infanticide has been an important selection pressure influencing orangutan behavior and the evolution of orangutan social systems. In this paper, we critically assess this suggestion. We begin by investigating whether wild orangutans have been studied for a sufficiently long period that we might reasonably expect to have detected infanticide if it occurs. We consider whether orangutan females exhibit counterstrategies typically employed by other mammalian females. We also assess the hypothesis that orangutan females form special bonds with particular "protector males" to guard against infanticide. Lastly, we discuss socioecological reasons why orangutan males may not benefit from infanticide. We conclude that there is limited evidence for female counterstrategies and little support for the protector male hypothesis. Aspects of orangutan paternity certainty, lactational amenorrhea, and ranging behavior may explain why infanticide is not a strategy regularly employed by orangutan males on Sumatra or Borneo.
The Geography of Trust and Betrayal: Moral disputes and Late Pleistocene dispersal
Open Quaternary, 2015
Emotional complexity, moral conflict and the motivations for dispersal events From after 100,000 years ago, modern humans moved out of Africa spreading faster than had any other human species, across deserts, mountain ranges and seas, to the furthest limits of the globe. The explanations as to why they undertook such journeys, despite the risks and often failing to survive, have eluded us. One particular frustration has been that ethnographic accounts which might help us to understand the rapid dispersal of human populations in the Late Pleistocene are almost unknownmodern hunter-gatherers which might provide an analogy are tied to politically defined boundaries with no unoccupied lands into which to move. We suspect that the processes driving dispersal exist as yet unrecognised in modern hunting and gathering populations. Freuchen notably recounts a rare documented case of dispersal into a new region amongst the Netsilik of the Canadian Arctic (Freuchen 1961: 116-118). Might the motivations for this founding population setting out into a new region provide us with an insight into mechanisms of dispersal which have yet to be explored? Freuchen describes the journey of Uvigsakavsik, with two other Netsilik men and their wives and children who set out alone into the most inhospitable of unoccupied arctic tundra in the early years of the twentieth century. They journeyed south from Thule around 500km into previously unoccupied land in Melville Bay in the hope of surviving there. There was no lack of resources or ecological reason for their journey. The motivations instead lay in a moral dispute. After being accused of lying, ignored by others and with tempers running increasingly high, Uvigsakavsik could no longer bear to stay and he and his wife left his native group, gathering together his allies, two men from different groups in similar positions who were both accused of murder, intending to form a new colony far away. Remarkably Uvigsakavsik's ' outlaw' colony survived, and they even accumulated a wealth of furs. After several years of ' cooling down time' and hardship Uvigsakavsik and his wife travelled back north, bringing with them many furs and reconciling with the original group. Moral tensions would erupt once again however, as after his wife died Uvigsakavsik returned to his untrustworthy ways. He stole two wives from other hunters, as well as stealing food and making threats to Sigdlu, the husband of one of the women he had taken. Uvigsakavsik was widely felt to be an upstart. This time, despite a climate of raised tempers, he made the mistake of staying. Sigdlu, and his ally, Odark, shot and killed Uvigsakavsik when the three went out hunting narwhal together. The Netsilik to which they belonged were careful to make sure that the authorities did not find out about what Freuchen terms 'polar justice'. Complex and powerful emotions like desires for justice, resentment, altruistic punishment, motivations to take vengeance, jealousy, pride, forgiveness, a need for belonging and commitments to shared ethics drove this example of a successful founding colony in previously unoccupied lands. Were these emotions also part of the
The Nature and Function of Languages
Languages
Several studies in philosophy, linguistics and neuroscience have tried to define the nature and functions of language. Cybernetics and the mathematical theory of communication have clarified the role and functions of signals, symbols and codes involved in the transmission of information. Linguistics has defined the main characteristics of verbal communication by analyzing the main tasks and levels of language. Paleoanthropology has explored the relationship between cognitive development and the origin of language in Homo sapiens. According to Daniel Dor, language represents the most important technological invention of human beings. Seemingly, the main function of language consists of its ability to allow the sharing of the mind’s imaginative products. Following language’s invention, human beings have developed multiple languages and cultures, which, on the one hand, have favored socialization within communities and, on the other hand, have led to an increase in aggression between d...
The dynamics of social cohesion in response to simulated intergroup conflict in banded mongooses
Ecology and Evolution, 2021
Intergroup conflict is widespread in nature and is proposed to have strong impacts on the evolution of social behavior. The conflict–cohesion hypothesis predicts that exposure to intergroup conflict should lead to increased social cohesion to improve group success or resilience in future conflicts. There is evidence to support this prediction from studies of affiliative responses to outgroup threats in some animal societies. However, most of these studies have focused on behavioral changes over short time periods (minutes and hours after exposure to an outgroup), and hence very little is known about the dynamics and durability of responses to intergroup conflict over the longer term. We investigated this question by simulating intergroup encounters in wild banded mongooses (Mungos mungo) and measuring social behavior before, during, and after these encounters over a 5‐day period. We also ran control trials with non‐threatening stimuli. Banded mongooses reacted immediately to intrusi...
Ethology, 2021
Conflicts between stable social groups ("intergroup conflicts") can be damaging and exert a strong influence on within-group social behaviour. The success of groups during intergroup conflict may depend on the ability of individual group members to converge upon collective defence behaviour, such as approaching or attacking. In principle, collective defence can be achieved via a united front, in which each individual responds in the same way to an intergroup threat. We tested the impact of simulated intergroup conflicts on collective defence and individual behaviour in banded mongooses (Mungos mungo), a cooperatively breeding mammal in which intergroup conflict is particularly common and costly. We presented focal groups with scent markings, call playbacks and caged live animals from rival groups and compared their responses to these stimuli with their responses to own-group control stimuli. A greater proportion of group members approached the stimulus and acted defensively in response to rival stimuli as compared to controls, consistent with a unified collective defence response. However, counter to our expectation, groups exhibited lower behavioural homogeneity when presented with rival stimuli as compared to controls. A closer examination of the behaviours competitors used revealed that lower homogeneity was driven by a greater use, and diversity, of defensive behaviours relevant to repelling simulated rivals. Finally, group size affected responses: as group size increased, the proportion of members approaching the stimulus and behavioural homogeneity decreased. Our results lend support to the hypothesis that intergroup conflict leads to coordinated collective defence behaviour during the immediate threat of an intergroup conflict. However, collective defence need not mean that all group members execute the same behaviours.
Journal of Human Evolution, 2020
Compared with most mammals, postnatal development in great apes is protracted, presenting both an extended period of phenotypic plasticity to environmental conditions and the potential for sustained mother-offspring and/or sibling conflict over resources. Comparisons of cortisol levels during ontogeny can reveal physiological plasticity to species or population specific socioecological factors and in turn how these factors might ameliorate or exaggerate mother-offspring and sibling conflict. Here, we examine developmental patterns of cortisol levels in two wild chimpanzee populations (Budongo and Taï), with two and three communities each, and one wild bonobo population (LuiKotale), with two communities. Both species have similar juvenile life histories. Nonetheless, we predicted that key differences in socioecological factors, such as feeding competition, would lead to interspecific variation in mother-offspring and sibling conflict and thus variation in ontogenetic cortisol patterns. We measured urinary cortisol levels in 1394 samples collected from 37 bonobos and 100 chimpanzees aged up to 12 years. The significant differences in age-related variation in cortisol levels appeared population specific rather than species specific. Both bonobos and Taï chimpanzees had comparatively stable and gradually increasing cortisol levels throughout development; Budongo chimpanzees experienced declining cortisol levels before increases in later ontogeny. These age-related population differences in cortisol patterns were not explained by mother-offspring or sibling conflict specifically; instead, the comparatively stable cortisol patterns of bonobos and Taï chimpanzees likely reflect a consistency in experience of competition and the social environment compared with Budongo chimpanzees, where mothers may adopt more variable strategies related to infanticide risk and resource availability. The clear population-level differences within chimpanzees highlight potential intraspecific flexibility in developmental processes in apes, suggesting the flexibility and diversity in rearing strategies seen in humans may have a deep evolutionary history.
Wild chimpanzees’ use of single and combined vocal and gestural signals
Behavioral Ecology and Sociobiology, 2017
We describe the individual and combined use of vocalizations and gestures in wild chimpanzees. The rate of gesturing peaked in infancy and, with the exception of the alpha male, decreased again in older age groups, while vocal signals showed the opposite pattern. Although gesture-vocal combinations were relatively rare, they were consistently found in all age groups, especially during affiliative and agonistic interactions. Within behavioural contexts rank (excluding alpharank) had no effect on the rate of male chimpanzees' use of vocal or gestural signals and only a small effect on their use of combination signals. The alpha male was an outlier, however, both as a prolific user of gestures and recipient of high levels of vocal and gesture-vocal signals. Persistence in signal use varied with signal type: chimpanzees persisted in use of gestures and gesture-vocal combinations after failure, but where their vocal signals failed they tended to add gestural signals to produce gesture-vocal combinations. Overall, chimpanzees employed signals with a sensitivity to the public/private nature of information, by adjusting their use of signal types according to social context and by taking into account potential out-ofsight audiences. We discuss these findings in relation to the various socio-ecological challenges that chimpanzees are exposed to in their natural forest habitats and the current discussion of multimodal communication in great apes. Significance statement All animal communication combines different types of signals, including vocalizations, facial expressions, and gestures. However, the study of primate communication has typically focused on the use of signal types in isolation. As a result, we know little on how primates use the full repertoire of signals available to them. Here we present a systematic study on the individual and combined use of gestures and vocalizations in wild chimpanzees. We find that gesturing peaks in infancy and decreases in older age, while vocal signals show the opposite distribution, and patterns of persistence after failure suggest that gestural and vocal signals may encode different types of information. Overall, chimpanzees employed signals with a sensitivity to the public/private nature of information, by adjusting their use of signal types according to social context and by taking into account potential out-of-sight audiences.
American Journal of Primatology, 2021
Behavior is the interface through which animals interact with their environments, and therefore has potentially cascading impacts on the health of individuals, populations, their habitats, and the humans that share them. Evolution has shaped the interaction between species and their environments. Thus, alterations to the species-typical "wild-type" behavioral repertoire (and the ability of the individual to adapt flexibly which elements of the repertoire it employs) may disrupt the relationship between the organism and its environment, creating cascading One Health effects. A good example is rehabilitant orangutans where, for example, seemingly minor differences from wild conspecifics in the time spent traveling on the ground rather than in the forest canopy can affect an individual's musculoskeletal and nutritional health, as well as social integration. It can also increase two-way transmission of infectious diseases and/or pathogens with local human populations, or potentially with neighboring wild populations if there are no geographical barriers and rehabilitants travel far enough to leave their release area. Primates are well known ecosystem engineers, reshaping plant communities and maintaining biodiversity through seed dispersal, consuming plants, and creating canopy gaps and trails. From the habitat perspective, a rehabilitant orangutan which does not behave like a wild orangutan is unlikely to fulfill these same ecosystem services. Despite the importance of the diversity of an ape's behavioral repertoire, how it compares to that of wild conspecifics and how it alters in response to habitat variation, behavior is an often under-appreciated aspect of One Health. In this review, focusing on orangutans as an example of the kinds of problems faced by all captive great apes, we examine the ways in which understanding and facilitating the expression of wildtype behavior can improve their health, their ability to thrive, and the robustness of local One Health systems.