Bonobo

The bonobo (Pan paniscus), also historically called the pygmy chimpanzee and less often, the dwarf or gracile chimpanzee, is an endangered and one of the two species making up the genus Pan; the other being the common chimpanzee (Pan troglodytes).

Quotes

 * All the great ape species are known tool users in both the wild and captivity, although there is great variation in ability and behavioral repertoire. Differences in tool use acquisition between chimpanzees and gorillas have been attributed to differing levels of social tolerance as a result of differences in social structure. Chimpanzees also show sex differences in acquisition and both chimpanzees and bonobos demonstrate a female bias in tool use behaviors. Studies of acquisition are limited in the wild and between species comparisons are complicated in captivity by contexts that often do not reflect natural conditions. Here we investigated tool use acquisition in a captive group of naïve bonobos by simulating naturalistic conditions. We constructed an artificial termite mound fashioned after those that occur in the wild and tested individuals within a social group context. We found sex differences in latencies to attempt and to succeed where females attempted to fish, were successful more quickly, and fished more frequently than males. We compared our results to those reported for chimpanzees and gorillas. Males across all three species did not differ in latency to attempt or to succeed. In contrast, bonobo and chimpanzee females succeeded more quickly than did female gorillas. Female bonobos and female chimpanzees did not differ in either latency to attempt or to succeed. We tested the social tolerance hypothesis by investigating the relationship between tool behaviors and number of neighbors present. We also compared these results to those reported for chimpanzees and gorillas and found that bonobos had the fewest numbers of neighbors present. The results of this study do not support the association between number of neighbors and tool behavior reported for chimpanzees. However, bonobos demonstrated a similar sex difference in tool use acquisition, supporting the hypothesis of a female bias in tool use in Pan.
 * Klaree J Boose, Frances J White, Audra Meinelt, “Sex differences in tool use acquisition in bonobos (Pan paniscus)“, Am J Primatol, 2013 Sep;75(9):917-26.


 * Human language is a fundamentally cooperative enterprise, embodying fast-paced and extended social interactions. It has been suggested that it evolved as part of a larger adaptation of humans' species-unique forms of cooperation. Although our closest living relatives, bonobos and chimpanzees, show general cooperative abilities, their communicative interactions seem to lack the cooperative nature of human conversation. Here, we revisited this claim by conducting the first systematic comparison of communicative interactions in mother-infant dyads living in two different communities of bonobos (LuiKotale, DRC; Wamba, DRC) and chimpanzees (Taï South, Côte d'Ivoire; Kanyawara, Uganda) in the wild. Focusing on the communicative function of joint-travel-initiation, we applied parameters of conversation analysis to gestural exchanges between mothers and infants. Results showed that communicative exchanges in both species resemble cooperative turn-taking sequences in human conversation. While bonobos consistently addressed the recipient via gaze before signal initiation and used so-called overlapping responses, chimpanzees engaged in more extended negotiations, involving frequent response waiting and gestural sequences. Our results thus strengthen the hypothesis that interactional intelligence paved the way to the cooperative endeavour of human language and suggest that social matrices highly impact upon communication styles.
 * Marlen Fröhlich, Paul Kuchenbuch, Gudrun Müller, Barbara Fruth, Takeshi Furuichi, Roman M Wittig, Simone Pika; “Unpeeling the layers of language: Bonobos and chimpanzees engage in cooperative turn-taking sequences.”, Sci Rep, 2016 May 23;6:25887.


 * Although chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) are closely related, females of the two species show surprisingly large differences in many behavioral aspects. While female chimpanzees tend to range alone or in small parties during non-estrous periods, female bonobos aggregate even more often than do males. Female chimpanzees do not have frequent social interactions with other females, whereas female bonobos maintain close social associations with one another. Although the ranging patterns of chimpanzee parties are generally led by males, female bonobos often take the initiative in ranging behavior. While female chimpanzees usually do not exhibit estrus during postpartum amenorrhea or pregnancy, female bonobos exhibit a prolonged pseudo-estrus during such non-conceptive periods. Studies of these two species have also shown great differences in agonistic behaviors performed by males. Male chimpanzees frequently fight with other males to compete for estrous females, but male bonobos seldom do so. While there are many records of infanticide by male chimpanzees, there is no confirmed record of such an event among bonobos. Several cases of within-group killing among adult male chimpanzees have been reported, but there is no such record for bonobos. While intergroup conflicts among chimpanzees sometimes involve killing members of the other group, intergroup conflicts among bonobos are considerably more moderate. In some cases, bonobos from two different groups may even range together for several days while engaging in various peaceful interactions. I will address two important questions that arise from these comparisons, exploring why females of such closely related species show such clear differences in behavior and whether or not the behavioral characteristics of female bonobos contribute to the peaceful nature of bonobo society.
 * Takeshi Furuichi, “Female contributions to the peaceful nature of bonobo society “, Evol Anthropol, Jul-Aug 2011;20(4):131-42.


 * Chimpanzees (Pan troglodytes) and bonobos (P. paniscus) are our closest living relatives, with the human lineage diverging from the Pan lineage only around five to seven Mya, but possibly as early as eight Mya.1-2 Chimpanzees and bonobos even share genetic similarities with humans that they do not share with each other. Given their close genetic relationship to humans, both Pan species represent crucial living models for reconstructing our last common ancestor (LCA) and identifying uniquely human features. Comparing the similarities and differences of the two Pan is thus essential for constructing balanced models of human evolution.
 * Thibaud Gruber, Zanna Clay; “A Comparison Between Bonobos and Chimpanzees: A Review and Update”, Evol Anthropol, 2016 Sep;25(5):239-252.


 * The author studied wild pygmy chimpanzees (Pan paniscus) for about eight months on two separate expeditions between 1975 and 1977, in the study area located at Wamba, Zone de Djolu, in the Republic of Zaire. Most of this paper is based on data obtained through observing the pygmy chimpanzees in their natural surroundings. However, some of them were provisioned and frequently visited the feeding area. Some portion of the data on groupings and food sharing were gathered there. Pygmy chimpanzees groupings, although similar to the common chimpanzee groupings, have larger temporary associations that are almost exclusively bisexual. At least in some greeting contexts, they exhibit patterns of behavior distinctly different from the common chimpanzee. A preliminary investigation of their social interactions revealed strong bonds between males and females, and high female sociability, in contrast to the strong male bonds and female unsociability seen among common chimpanzees.
 * Takayoshi Kano, “Social behavior of wild pygmy chimpanzees (Pan paniscus) of Wamba: A preliminary report”, Journal of Human Evolution, Volume 9, Issue 4, May 1980, Pages 243-254, IN1-IN2, 255-260


 * Applying well-established psychological paradigms to our closest relatives represents a promising approach for providing insight into similarities and differences between humans and apes. Numerous articles have been published on the dot-probe task, showing that humans have an attentional bias toward emotions, especially when threatening. For social species like primates, efficiently responding to others’ emotions has great survival value. Observational research has shown that, compared with humans and chimpanzees, bonobos excel in regulating their own and others’ emotions, thereby preventing conflicts from escalating. The present study is an initial effort to apply a psychological test to the bonobo, and demonstrates that they, like humans, have heightened attention to emotional—compared with neutral—conspecifics, but are mostly drawn toward protective and affiliative emotions.
 * Mariska E. Kret, Linda Jaasma, Thomas Bionda, and Jasper G. Wijnen; “Bonobos (Pan paniscus) show an attentional bias toward conspecifics’ emotions”, (March 14, 2016)


 * In social animals, the fast detection of group members’ emotional expressions promotes swift and adequate responses, which is crucial for the maintenance of social bonds and ultimately for group survival. The dot-probe task is a well-established paradigm in psychology, measuring emotional attention through reaction times. Humans tend to be biased toward emotional images, especially when the emotion is of a threatening nature. Bonobos have rich, social emotional lives and are known for their soft and friendly character. In the present study, we investigated (i) whether bonobos, similar to humans, have an attentional bias toward emotional scenes compared with conspecifics showing a neutral expression, and (ii) which emotional behaviors attract their attention the most. As predicted, results consistently showed that bonobos’ attention was biased toward the location of the emotional versus neutral scene. Interestingly, their attention was grabbed most by images showing conspecifics such as sexual behavior, yawning, or grooming, and not as much—as is often observed in humans—by signs of distress or aggression. The results suggest that protective and affiliative behaviors are pivotal in bonobo society and therefore attract immediate attention in this species.
 * Mariska E. Kret, Linda Jaasma, Thomas Bionda, and Jasper G. Wijnen; “Bonobos (Pan paniscus) show an attentional bias toward conspecifics’ emotions”, (March 14, 2016)


 * The dichotomy between the two Pan species, the bonobo (Pan paniscus) and chimpanzee (Pan troglodytes) has been strongly emphasized until very recently. Given that most studies were primarily based on adult individuals, we shifted the "continuity versus discontinuity" discussion to the infant and juvenile stage. Our aim was to test quantitatively, some conflicting statements made in literature considering species differences between immature bonobos and chimpanzees. On one hand it is suggested that infant bonobos show retardation in motor and social development when compared with chimpanzees. Additionally it is expected that the weaning process is more traumatic to chimpanzee than bonobo infants. But on the other hand the development of behaviors is expected to be very similar in both species. We observed eight mother-infant pairs of each species in several European zoos. Our preliminary research partially confirms that immature chimpanzees seem spatially more independent, spending more time at a larger distance from their mother than immature bonobos. However, the other data do not seem to support the hypothesis that bonobo infants show retardation of motor or social development. The development of solitary play, environmental exploration, social play, non-copulatory mounts and aggressive interactions do not differ between the species. Bonobo infants in general even groom other group members more than chimpanzee infants. We also found that older bonobo infants have more nipple contact than same aged chimpanzees and that the weaning process seems to end later for bonobos than for immature chimpanzee. Additionally, although immature bonobos show in general more signs of distress, our data suggest that the weaning period itself is more traumatic for chimpanzees.
 * Mieke De Lathouwers, Linda Van Elsacker, “Comparing infant and juvenile behavior in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes): a preliminary study”, Primates. 2006 Oct;47(4):287-93. doi: 10.1007/s10329-006-0179-7. Epub 2006 May 9.


 * Sexual behavior by infecundable females, and by same-sex and adult-immature dyads, occurs in wild and captive bonobos (Pan paniscus). Proposed functions of these behaviors, in social primates generally, include practice, paternity confusion, exchange, and communication as well as appeasement. We used this framework to interpret and to compare observations of sexual behavior in a captive bonobo group and a wild white-faced capuchin (Cebus capucinus) group. In both species, (a) sexual behavior was no more frequent in cycling females than in pregnant or lactating females and (b) same-sex and adult-immature dyads engaged in as much mounting or genitogenital contact as adult heterosexual dyads did. The species differed in that (a) bonobos engaged in sexual behavior 65 times as frequently as capuchins, (b) only bonobos engaged in sexual contact other than ventrodorsal mounting during focal observation, and (c) bonobo sexual contact was concentrated most heavily in socially tense situations in adult female–female dyads, whereas capuchin sexual contact was concentrated most heavily in socially tense situations in adult male–male dyads. These data and published literature indicate that (a) practice sex occurs in both species, (b) paternity confusion may be a current function of C. capucinus nonconceptive sex, (c) exchange sex remains undemonstrated in capuchins, and (d) communication sex is more important to members of the transferring sex—female bonobos and male capuchins—than to members of the philopatric sex.
 * Joseph H. Manson, Susan Perry & Amy R. Parish; “Nonconceptive Sexual Behavior in Bonobos and Capuchins”, International Journal of Primatology, volume 18, pages767–786, (Published: October 1997)


 * In the mid-1970s, Japanese primatologist Takayoshi Kano was one of the first to document the central position of females in bonobo society. This contrasts with chimpanzees, where females tend to spend a lot of time marginalised at the edge of the community. Kano also observed lots of unusual sexual behaviour. “Genito-genital rubbing”, for instance, usually began with female A approaching and staring into the face of female B. The pair would then embrace “and begin to rub each other’s genitals together (probably clitoris) rhythmically and rapidly,” he wrote in 1980 in the Journal of Human Evolution. This typically lasted for less than 20 seconds, and occasionally for over a minute. When males and females copulated, Kano recorded that in around one-third of cases, the pair would adopt the missionary position. In a few instance, he saw females mating with different males and sometimes with juveniles or infants. This is all true, but the public fascination with these behaviours has given rise to a view of bonobos that is a little extreme, says Zanna Clay of the University of Birmingham in the UK, who has spent years studying wild bonobos. “There is this perception that they have sex all the time, that they are like nymphomaniacs.” The reality is more nuanced. The frequency of copulation in bonobos is not as high as most people assume, she says. “In terms of reproduction they are not more sexually active than chimps.”
 * Henry Nicholls,, BBC, (17 March 2016)


 * “In bonobos, females show estrus and have sexual intercourse with males even during the period they can’t conceive,” he says. This is very different from the relatively limited sexuality of female chimps, but could have arisen as a result of just a few genetic changes in that founding population, says Furuichi. With many females sexually active at once, there would have been less and less competition between males, until eventually the females took control. The rest, as they say, is evolutionary history.
 * Takeshi Furuichi as qtd by Henry Nicholls,, BBC, (17 March 2016)


 * This study compares adult play behavior in the two Pan species in order to test the effects of phylogenetic closeness and the nature of social systems on play distribution. The social play (both with fertile and immature subjects) performed by adults did not differ between the two species. In contrast, in bonobos, play levels among fertile subjects were higher than in chimpanzees. Findings regarding levels of undecided conflicts (more frequent in bonobos) and formal submission displays (lacking in bonobos) confirm, in the two colonies under study, that bonobos exhibit "egalitarianism" more than chimpanzees. Some authors emphasized the importance of play-fighting for social assessment when relationships among individuals are not codified and structured according to rank-rules. Indeed, adult bonobos played more roughly than chimpanzees. Moreover, adult bonobos displayed the full play-face at a high frequency especially during rough play sessions, whereas in chimpanzees, the frequency of play signals was not affected by roughness of play. The frequency of social play among bonobo females was higher than in any other sex combinations, whereas no difference was found for chimpanzees. As a matter of fact, social play can be viewed as a balance between cooperation and competition. Among bonobo females, characterized by social competence and affiliation, social play might enhance their behavioral flexibility and increase their socially symmetrical relationships which, after all, are the basis for their egalitarian society.
 * Elisabetta Palagi, “Social play in bonobos (Pan paniscus) and chimpanzees (Pan troglodytes): Implications for natural social systems and interindividual relationships”, Am J Phys Anthropol, 2006 Mar;129(3):418-26.


 * Inferences for female bonding in humans have drawn on models derived from studies of nonhuman primates. In primates, strong affiliative relationships between unrelated females are rare. This is true for the social systems of apes and particularly for those of the closest living relatives of humans, the chimpanzee (Pan troglodytes). However, the other member of the genus Pan, the bonobo (Pan paniscus) is strikingly different in this regard as evidenced from the present comparative study that was conducted at the Wilhelma Zoo, Germany. A group of bonobos and of chimpanzees was each provided with limited access to an artificial “fishing” site (a simulated termite mound) filled with desirable food. In chimpanzees, the adult male was dominant over all females and able to monopolize the food. In bonobos, on the other hand, the adult bonobo male was low ranking, and females controlled food access. Sex between bonobo females apparently facilitated affiliative encounters between females in the context of feeding. Until now, studies of exchanges of sex-for-food focused on heterosexual interactions. This study reveals that trading of sex for food occurs regularly between bonobo females. These exchanges appear to reduce tension and facilitate female cofeeding and cooperation. They help create stable long-term relationships among females that result in coalition formation, control of food resources, and ability to elevate their dominance status relative to males well above that of their chimpanzee counterparts. The strong affiliative relationships between unrelated female bonobos provide an alternative model from which predictions for bonding among human females can be generated.
 * Amy Randall Parish, ”Sex and food control in the “uncommon chimpanzee”: How Bonobo females overcome a phylogenetic legacy of male dominance”, Ethology and Sociobiology, Volume 15, Issue 3, May 1994, Pages 157-179


 * In long–lived social mammals such as primates, individuals can benefit from social bonds with close kin, including their mothers. In the patrilocal chimpanzee (Pan troglodytes spp.) and bonobo (Pan paniscus), sexually mature males reside and reproduce in their natal groups and can retain post-dependency bonds with their mothers, while immatures of both sexes might also have their paternal grandmothers available. However, quantitative information on the proportion of males and immatures that co-reside with both types of these close female relatives is limited for both species. Combining genetic parentage determination and group composition data from five communities of wild chimpanzees and three communities of wild bonobos, we estimated the frequency of co-residence between (1) mature males and their mothers, and (2) immature males and females and their paternal grandmothers. We found that adult males resided twice as frequently with their mothers in bonobos than in chimpanzees, and that immature bonobos were three times more likely to possess a living paternal grandmother than were immature chimpanzees. Patterns of female and male survivorship from studbook records of captive individuals of both species suggest that mature bonobo females survive longer than their chimpanzee counterparts, possibly contributing to the differences observed in mother–son and grandmother–immature co-residency levels. Taking into account reports of bonobo mothers supporting their sons' mating efforts and females sharing food with immatures other than their own offspring, our findings suggest that life history traits may facilitate maternal and grandmaternal support more in bonobos than in chimpanzees.
 * Grit Schubert, Linda Vigilant, Christophe Boesch, Reinhard Klenke, Kevin Langergraber, Roger Mundry, Martin Surbeck, and Gottfried Hohmann, “Co–Residence between Males and Their Mothers and Grandmothers Is More Frequent in Bonobos Than Chimpanzees”, PLoS One, 2013; 8(12): e83870.


 * The gestural repertoires of bonobos and chimpanzees are well documented, but the relationship between gestural signaling and positional behavior (i.e., body postures and locomotion) has yet to be explored. Given that one theory for language evolution attributes the emergence of increased gestural communication to habitual bipedality, this relationship is important to investigate.
 * Lindsey W Smith, Roberto A Delgado; “Body language: The interplay between positional behavior and gestural signaling in the genus Pan and its implications for language evolution”, Am J Phys Anthropol, 2015 Aug;157(4):592-602.


 * As our closest living relatives, chimpanzees and bonobos have been widely used as models of the behavior of early hominids. In recent years, as information on the social behavior and ecology of bonobos has come to light, many interspecific comparisons have been made. Chimpanzees have been characterized in terms of their intercommunity warfare, meat eating, infanticide, cannibalism, male status‐striving, and dominance over females. Bonobos, meanwhile, have been portrayed as the “Make love, not war” ape, characterized by female power‐sharing, a lack of aggression between either individuals or groups, richly elaborated sexual behavior that occurs without the constraint of a narrow window of fertility, and the use of sex for communicative purposes. This paper evaluates the evidence for this dichotomy and considers the reasons that contrasting portrayals of the two great apes have developed. While there are marked differences in social behavior between these two species, I argue that they are more similar behaviorally than most accounts have suggested. I discuss several reasons that current views of bonobo and chimpanzee societies may not accord well with field data. Among these are a bias toward captive data on bonobos, the tendency to see bonobos as derived because their behavior has been described more recently than that of chimpanzees, and the possibility that interpretations of bonobo‐chimpanzee differences are reflections of human male‐female differences.
 * Craig B. Stanford, “The Social Behavior of Chimpanzees and Bonobos: Empirical Evidence and Shifting Assumptions”, Current Anthropology, Vol. 39, No. 4 (August/October 1998), pp. 399-420


 * Molecular studies indicate that humans, chimpanzees (“Pan troglodytes”), and bonobos (P. paniscus”) are very closely related in a lineage that split into hominid an “Pan” lines approximately 6-7 million years ago, possibly following divergence from the gorilla lineage about 1-2 million year earlier (Caccone and Powell 1989, Ruvolo et al. 1991). Chimpanzees and bonobos have a more recent common ancestry only some 2-25 million years ago (Caccone and Powerll 1989). Although it is now an engendered species, the chimpanzee is an extremely successful species ecologically, occurring in a wide range of habitat types across the equatorial portion of the African continent. The bonobo, by contrast is found in a much more geographically and ecologically restricted region of lowland rain forest in central Zaire. Until the 1980s, so little was known about the behavior of wild bonobos that detailed comparisons between the two “Pan” species were not possible. The number of field observation hours on bonobos is today still a small fraction of the database of chimpanzee behavior and ecology (White 1996”a”), but cross-species comparisons are nevertheless commonplace.
 * Craig B. Stanford, “The Social Behavior of Chimpanzees and Bonobos: Empirical Evidence and Shifting Assumptions”, Current Anthropology, Vol. 39, No. 4 (August/October 1998), p.399


 * Chimpanzees have long been described in terms of male dominance over females, hunting and meat eating, and intercommunity warfare. According to Wrangham and Peterson (1996:191), “What most male chimpanzees strive for is being on top, the one position where they will never have to grovel. It is the difficulty of getting there that induces aggression.” Bonobos have been seen as sharply contrasting with chimpanzees, displaying female dominance over males, richly elaborated sexual behavior that often occurs in a nonconceptive context, and a general lack of aggressiveness. In de Waal’s (1997:22) description, “Bonobo society, unlike that of chimpanzees, is best characterized as female centered and egalitarian, with sex substituting for aggression. Females occupy prominent, often ruling positions in society, and the high points of bonobo intellectual life are found not in cooperative hunting or strategies to achieve dominance but in conflict resolution and sensitivity to others.” The importance of these closely related apes in the ontogeny of theories about the origins of human behavior cannot be overstated.
 * Craig B. Stanford, “The Social Behavior of Chimpanzees and Bonobos: Empirical Evidence and Shifting Assumptions”, Current Anthropology, Vol. 39, No. 4 (August/October 1998), p.399


 * While investigating the genetic structure in wild bonobos, we realized that the widely accepted scenario positing that the Pleistocene appearance of the Congo River separated the common ancestor of chimpanzees (Pan troglodytes) and bonobos (P. paniscus) into two species is not supported by recent geographical knowledge about the formation of the Congo River. We explored the origin of bonobos using a broader biogeographical perspective by examining local faunas in the central African region. The submarine Congo River sediments and paleotopography of central Africa show that the Congo River has functioned as a geographical barrier for the last 34 million years. This evidence allows us to hypothesize that when the river was first formed, the ancestor of bonobos did not inhabit the current range of the species on the left bank of the Congo River but that, during rare times when the Congo River discharge decreased during the Pleistocene, one or more founder populations of ancestral Pan paniscus crossed the river to its left bank. The proposed scenario for formation of the Congo River and the corridor hypothesis for an ancestral bonobo population is key to understanding the distribution of great apes and their evolution.
 * Hiroyuki Takemoto, Yoshi Kawamoto, Takeshi Furuichi, “How did bonobos come to range south of the congo river? Reconsideration of the divergence of Pan paniscus from other Pan populations", Evolutionary Anthropology, Volume24, Issue5, September/October 2015, p.170


 * Co-author, who heads the UO Department of Anthropology and has extensively studied bonobos in Africa, said the study provides helpful information. "It is common in the wild to see infant bonobos be a focus of enormous interest to others, especially to adolescent bonobos," White said. "It is often noticeable how bonobo mothers are willing to let others get close and interact with their infants, as compared to chimpanzees who are more restrictive."
 * Frances White as quoted in "Insight into infant handling by young bonobos.", by Jim Barlow, University of Oregon, ScienceDaily, (19 June 2018).


 * Bonobos have been observed to use socio-sexual behavior at higher frequency than chimpanzees. Little is known about the developmental influences that shape this behavior in bonobos.
 * Vanessa Woods, Brian Hare; “Bonobo but not chimpanzee infants use socio-sexual contact with peers.”, Primates, 2011 Apr;52(2):111-6.


 * Even as infants, bonobos use socio-sexual behavior, whereas the same behavior is completely absent in chimpanzee infants. Bonobos used a range of socio-sexual behavior with a range of partners, including positioning that is non-reproductive and frequently with same-sex partners. Consistent with what has been observed in adult bonobos in captivity and the wild, infant bonobos show a high frequency of socio-sexual behavior when food is present. Taken together with previous studies showing a relationship between socio-sexual behavior and feeding (Kuroda1980; Kano1980; de Waal1987; Paoli et al.2007), these findings suggest that socio-sexual behavior in bonobos serves some function during social feeding that is not closely tied to reproduction.
 * Vanessa Woods, Brian Hare; “Bonobo but not chimpanzee infants use socio-sexual contact with peers”, Primates, (Received: 18 August 2010 / Accepted: 2 November 2010), p.5


 * [I]t is important to note that the infant bonobos showed little sexual behavior outside feeding time. Moreover, while it has been suggested that in many regards bonobos are juvenilized relative to chimpanzees; this pattern of behavior in bonobos seems to actually suggest earlier onset of sexual behavior in this species (Shea1983; Lieberman et al.2007; Wobber et al.2010b). If bonobos are the more derived species of Pan, then the selection pressure(s) that led to their evolution did not simply lead to juvenilization (e.g. bonobos develop sexual behavior before chimpanzees). Instead, it may be that selection against aggression in bonobos shaped their development so they behave like juveniles throughout life. To make this possible, behavior observed in chimpanzees is expressed earlier whereas other behavior is expressed later or not at all in bonobos. If true, what may unify all the changes is that they led to a pattern of development that promotes less severe forms of aggression in this species (Wrangham and Pilbeam 2001).
 * Vanessa Woods, Brian Hare; “Bonobo but not chimpanzee infants use socio-sexual contact with peers”, Primates, (Received: 18 August 2010 / Accepted: 2 November 2010), p.5

”Sex and strife: post-conflict sexual contacts in bonobos” (15 October 2013)
Zanna Clay and Frans B.M. de Waal, ”Sex and strife: post-conflict sexual contacts in bonobos”, Behaviour, (15 October 2013)
 * Sexual contacts are thought to play an important role in regulating social tension in bonobos (Panpaniscus), and are especially common following aggressive conflicts, either between former opponents or involving bystanders. Nevertheless, research on the factors determining post-conflict sexual contacts, their effectiveness in reducing social tension and the nature of post-conflict sexual behaviour is scarce. Here, we collected data on post-conflict affiliative contacts in bonobos occurring between former opponents (reconciliation) and offered by bystanders towards victims (consolation) to investigate the role of sexual contacts in the regulation of aggressive conflicts compared to non-sexual affiliation behaviours. We tested whether post-conflict sexual contacts:(1) alleviate stress, (2) confer reproductive benefits, (3) mediate food-related conflict and (4) re-pair valuable social bonds. Thirty-six semi-free bonobos of all ages were observed at the Lola yaBonobo Sanctuary, DR Congo, using standardized Post-Conflict/Matched Control methods. Consolation and reconciliation were both marked by significant increases in the occurrence of sexual behaviours. Reconciliation was almost exclusively characterized by sexual contacts, although consolation was also characterized by increases in non-sexual behaviours, such as embrace. Adults were more likely to engage in post-conflict sexual contacts than younger bonobos. Consistent with the stress-alleviation hypothesis, victims receiving sexual consolatory contact showed significantly lower rates of self-scratching, a marker of stress in primates, compared to receiving non-sexual contact. Post-conflict sexual contacts were not targeted towards valuable social partners and they did not confer obvious reproductive benefits; nor were they used to mediate food-related conflicts. Overall, results highlight the role of sex in regulating tension and social conflicts in bonobos.
 * p.1


 * Bonobos (Pan paniscus) are well known for possessing a particularly rich and heightened socio-sexuality (Thompson-Handler et al., 1984; de Waal,1987, 1995; Furuichi, 1989; Kano, 1989; White, 1996; Hashimoto, 1997;Hohmann & Fruth, 2000; Hohmann et al., 2009; Clay et al., 2011). Sex is freely incorporated into their daily life, with individuals habitually engaging in sexual interactions in all age and sex combinations. Bonobo females remain sexually active across their sexual cycles and, unlike most other primates, engage in face-to-face sexual interactions (e.g., Thompson-Handleret al., 1984; Kano, 1992; Paoli et al., 2006). Genito-genital contacts area hallmark of their socio-sexual behaviour, during which two individuals, most commonly females, embrace ventro-ventrally, swing their hips later-ally while keeping their vulva in contact (Kuroda, 1980; Hohmann & Fruth,2000, Figure 1) Socio-sexual contacts are thought to help regulate stress in bonobos, acting as a kind of ‘social grease’, to alleviate tension and to facilitate peaceful co-existence between group members, who generally lack close genetic ties(de Waal, 1987; Hohmann & Fruth, 2000; Fruth & Hohmann, 2006). Consistent with Hanby’s (1977) prediction about the stress relieving function of primate socio-sexual contacts, most non-conceptive sexual behaviours in bonobos occur within socially tense periods, such as feeding, anticipation of feeding, inter-group interactions and following aggressive conflicts (Mori,1983; de Waal, 1987; Manson et al., 1997; Hohmann & Fruth, 2000; Paoli et al., 2006; Hohmann et al., 2009). Like any socially foraging animal, feeding is a source of contention in bonobos and sex appears to regulate feeding competition and facilitate food sharing (i.e., Parish, 1994; Hohmann et al., 2009). For instance, individuals offering sexual contacts to food possessors are more likely to gain access to the feeding source (Kuroda, 1984; Thompson-Handler et al., 1984; deWaal, 1987; Kano, 1992). With the relation between food and tension, most studies focus have focused on socio-sexual behaviour in the feeding context(e.g., Parish, 1994; Hohmann et al., 2009), consequently leaving investigation into its role in other contexts somewhat neglected. In one study how-ever, Hohmann & Fruth (2000) showed that genital contacts in wild females increased between opponents following conflicts, a finding that warrants further investigation.
 * p.2


 * Following aggressive conflicts, former opponents often engage in various forms of affiliative contacts, a reparative process known as reconciliation (de Waal & van Roosmalen, 1979; de Waal & Aureli, 1996; Arnold et al.,2001). In bonobos, these contacts are more often sexual in nature (de Waal,1987, 1992; Manson et al., 1997; Hohmann & Fruth, 2000; Palagi et al.,2004), although various post-conflict behaviours are used in primates and other animals (e.g., de Waal, 1989; Fraser et al., 2008). For instance, chimpanzees reconcile primarily using embrace, kissing, ‘finger in mouth’ and touching (Fraser et al., 2008). In addition to reconciliation, uninvolved by-standers sometimes initiate affiliative contacts with one of the contestants, typically the former victim (de Waal & Roosmalen, 1979; de Waal & Aureli,1996). Bystanders can accrue various direct benefits by doing so, such as protection from redirected aggression (e.g., Fraser et al., 2009). In a select number of species, however, the offering of friendly contacts appears to be more driven by a motivation to reduce the distress of a close social partner or kin-member, based on an apparent absence of purely self-serving benefits (chimpanzees, P. troglodytes: e.g., de Waal & van Roosmalen, 1979; Koski &Sterck, 2007; Fraser & Aureli, 2008; Romero et al., 2011; bonobos: Palagiet al., 2004; Clay & de Waal, 2013a; gorillas, Gorilla gorilla: Cordoni etal., 2006; crows, C. corax: Fraser & Bugnyar, 2010: dogs, Canis familiaris: Cools et al., 2008; wolves, C. lupus: Palagi & Cordoni, 2009: African elephants, Loxodonta africana: Byrne et al., 2008). This type of affiliative act, known as ‘consolation’, has been shown to be effective in reducing the recipient distress (e.g., Fraser et al., 2008; Clay & de Waal, 2013a). With a shift towards the other, consolation is considered an important bridge between expressions of empathy in animals and humans, as it suggests that the consoler can recognize as well as respond appropriately to alleviate anothers’ distress (e.g., Preston & de Waal, 2002; Romero et al., 2010).
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 * Following aggressive conflict, bonobos use a suite of sexual and, to a lesser extent, non-sexual behaviours to reconcile with former opponents and, as bystanders, to console distressed victims. Reconciliation and consolation were marked by pronounced increases in sexual behaviours, which included genito-genital contacts, mounting, genital touch and, to a lesser extent, copulation. Reconciliation was almost exclusively characterized by sexual contacts. While sexual contacts were also the most frequently occurring consolatory behaviour, consolation included a rise in other behaviours (embrace, touch, contact peering and holding). Grooming, play, and contact sitting occurred more frequently during baseline, suggesting these behaviours are more relevant for down-tempo social affiliation. Adults were more likely to engage in post-conflict sexual behaviours than adolescents and juveniles, indicating that the sexual nature of conflict resolution strengthens with age in bonobos and that the mechanisms underlying post-conflict behaviours are likely to vary across development. In accordance with the tension regulation hypothesis, victims receiving sexual contact showed significantly lower rates of self-scratching compared to receiving non-sexual consolatory contact. While receiving any form of consolatory contact appears to be calming (as indicated by reduced self-scratching: Clay & de Waal, 2013a, b), the results further specify that sexual contacts are the most effective in doing so.
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