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Authors thank the Royal Zoological Society Scotland for the core funding they provide to the Budongo Conservation Field Station. Associating with kin provides individual benefits but requires that these relationships be detectable. In humans, facial phenotype matching might help assess paternity; however, evidence for it is mixed. In chimpanzees, concealing visual cues of paternity may be beneficial due to their promiscuous mating system and the considerable risk of infanticide by males. On the other hand, detecting kin can also aid chimpanzees in avoiding inbreeding and in forming alliances that improve kin-mediated fitness. Although previous studies assessing relatedness based on facial resemblance in chimpanzees exist, they used images of captive populations in whom selection pressures and reproductive opportunities are controlled and only assessed maternity or paternity of adult offspring. In natural populations, the chances of infanticide are highest during early infancy, suggesting that young infants would benefit most from paternity concealment, whereas adults and subadults would benefit from the detection of all types of kin, including half-siblings. In our experiment, we conducted an online study with human participants, in which they had to assess the relatedness of chimpanzees based on facial similarity. To address previous methodological constraints, we used chimpanzee images across all ages, as well as maternal and paternal half-siblings. We found that kin status was detected above chance across all relatedness categories, with easier kin detection of father-offspring pairs, females, and older chimpanzees. Together, these findings support the existence of paternity confusion in infant chimpanzees and provide a possible mechanism for incest avoidance and kin-based social alliances in older individuals. Postprint

Funding: Royal Zoological Society of Scotland provide core funding to Budongo Conservation Field Station. Finally, we thank the European Research Council for funding this project under Gestural Origins Grant No: 802719 and NCCR Evolving Language, Swiss National Science Foundation Agreement #51NF40_180888. Dialects are a cultural property of animal communication previously described in the signals of several animal species. While dialects have predominantly been described in vocal signals, chimpanzee leaf-clipping and other ‘leaf-modifying’ gestures, used across chimpanzee and bonobo communities, have been suggested as a candidate for cultural variation in gestural communication. Here we combine direct observation with archaeological techniques to compare the form and use of leaf-modifying gestures in two neighbouring communities of East African chimpanzees. We found that while both communities used multiple forms, primarily within sexual solicitation, they showed a strong preference for a single, different gesture form. The observed variation in form preference between these neighbouring communities within the same context suggests that these differences are, at least in part, socially derived. Our results highlight an unexplored source of variation and flexibility in gestural communication, opening the door for future research to explore socially derived dialects in non-vocal communication. Publisher PDF

In most languages, individual words can be ambiguous between several different meanings, but through syntax and context the intended meaning of an ambiguous word usually becomes apparent. Many great ape gestures also have ambiguous meanings, which poses the problem of how individuals can interpret the signaller’s intended meaning in specific instances. We tested the effects of sequence compositionality and situational context (including behavioural and interpersonal contexts) in wild bonobos (Pan paniscus) at Wamba, DRCongo. We found no effect on a gesture’s meaning from its presence and position in sequence. However, two aspects of situational context did affect meaning: behaviour of the signaller immediately prior to gesturing, and relative age/sex of signaller and recipient. The intended meaning of ambiguous gestures was almost completely disambiguated by means of these aspects of context. Our findings suggest that the use of contextual information to interpret ambiguous signals predates the uniquely-human lineage and is not specific to language.

Funding: This study was funded by an European Research Council Consolidator grant (ERC_CoG 2016_724608) awarded to KS (https://erc.europa.eu/funding/consolidator-grants). Joint attention, or sharing attention with another individual about an object or event, is a critical behaviour that emerges in pre-linguistic infants and predicts later language abilities. Given its importance, it is perhaps surprising that there is no consensus on how to measure joint attention in prelinguistic infants. A rigorous definition proposed by Siposova & Carpenter (2019) requires the infant and partner to gaze alternate between an object and each other (coordination of attention) and exchange communicative signals (explicit acknowledgement of jointly sharing attention). However, Hobson and Hobson (2007) proposed that the quality of gaze between individuals is, in itself, a sufficient communicative signal that demonstrates sharing of attention. They proposed that observers can reliably distinguish “sharing”, “checking”, and “orienting” looks, but the empirical basis for this claim is limited as their study focussed on two raters examining looks from 11-year-old children. Here, we analysed categorisations made by 32 naïve raters of 60 infant looks to their mothers, to examine whether they could be reliably distinguished according to Hobson and Hobson’s definitions. Raters had overall low agreement and only in 3 out of 26 cases did a significant majority of the raters agree with the judgement of the mother who had received the look. For the looks that raters did agree on at above chance levels, look duration and the overall communication rate of the mother were identified as cues that raters may have relied upon. In our experiment, naïve third party observers could not reliably determine the type of look infants gave to their mothers, which indicates that subjective judgements of types of look should not be used to identify mutual awareness of sharing attention in infants. Instead, we advocate the use of objective behaviour measurement to infer that interactants know they are ‘jointly’ attending to an object or event, and believe this will be a crucial step in understanding the ontogenetic and evolutionary origins of joint attention. Publisher PDF

Maternal cannibalism, whereby a mother consumes her own offspring, occurs in various animal taxa and is commonly explained by nutritional stress or environmental pressures. It is rare in nonhuman primates and is considered an aberrant behavior only observed under high-stress conditions. It was therefore surprising when, in the first reported case of cannibalism in wild bonobos, a mother consumed part of the dead infant at LuiKotale. Here we report two more cases of maternal cannibalism by wild bonobos at two different study sites, Wamba and Kokolopori. The dead infants' mothers participated in the cannibalism in both cases. At Kokolopori, although the mother did consume part of the carcass, it was held and shared by another dominant female. At Wamba, the mother was a dominant female within the community and was the primary consumer of the carcass. In both cases, cannibalism resembled other meat-eating events, with the dominant female controlling meat consumption. Infanticide was not observed in either case, but its occurrence could not be ruled out. Although rare, the occurrence of maternal cannibalism at three different study sites suggests that this may represent part of the behavioral repertoire of bonobos, rather than an aberrant behavior.

The 11th International Conference on the Evolution of Language (Evolang 11) was hosted at the Lavin-Bernick Center for University Life at Tulane University in New Orleans, LA, USA, from 21 March to 24 March 2016. The University of Southern Mississippi organised the conference, with Heidi Lyn as Chair of the local organising committee. Over 200 delegates gathered for this second American Evolang, and were treated not only to a wide range of current research in language origins and evolution, but also to local ‘NOLA’ food and culture as well. Evolang hosted a reception at Mardi Gras World—a stylised warehouse storing numerous Mardi Gras floats and costumes, where guests were serenaded with a brass band and committee members threw beads into the amused, cocktail-sipping crowd. The conference banquet was held at the colonial-era-style Audubon Tea Room with live jazz and a swing dancing lesson led by Thom Scott-Phillips. Post-conference events included a ghost tour, swamp tours, and a plantation tour. This was the 20th anniversary of the very first Evolang, held in Edinburgh in 1996, and saw the release of the first issue of the Journal of Language Evolution . With a 20-year history, it is hardly surprising that there has been a strong ‘self-reflective’ tendency at recent Evolang conferences, as witnessed, for example, in the ‘Perspectives on Evolang’ section in the proceedings of Evolang 10 (Cartmill et al. 2014), as well as in some of the contributions in the first issue of JoLE (Dediu and de Boer 2016; Hammarstrom 2016). Something that is repeatedly mentioned in these publications is the observation that ‘work on language evolution has become much more rigorous: we are discovering methods by which questions we could formerly only speculate about can now be investigated empirically’ (de Boer 2014). These ‘self-reflective’ tendencies were also exemplified …

Summary Some scientists have suggested that, among Hominidae, prolonged postmenopausal longevity evolved uniquely in humans [1], while others disagree [2]. There have, however, been few empirical studies on how physiological aging and somatic durability in humans compare to our closest relatives — chimpanzees and bonobos [3]. If prolonged lifespan is selected for in humans, physiological aging, including reproductive and somatic senescence, might be different for Pan and Homo . But it seems that the parameters of reproductive senescence, such as the age of having their final offspring and the number of years between generations, are not very different between chimpanzee and human females [4]. Here, we report evidence for five cases of long-sightedness (presbyopia) in old wild bonobos, exhibited during grooming. Our results suggest that senescence of the eye has not changed much since the divergence of Pan and Homo from their common ancestor.

Great apes give gestures deliberately and voluntarily, in order to influence particular target audiences, whose direction of attention they take into account when choosing which type of gesture to use. These facts make the study of ape gesture directly relevant to understanding the evolutionary precursors of human language; here we present an assessment of ape gesture from that perspective, focusing on the work of the "St Andrews Group" of researchers. Intended meanings of ape gestures are relatively few and simple. As with human words, ape gestures often have several distinct meanings, which are effectively disambiguated by behavioural context. Compared to the signalling of most other animals, great ape gestural repertoires are large. Because of this, and the relatively small number of intended meanings they achieve, ape gestures are redundant, with extensive overlaps in meaning. The great majority of gestures are innate, in the sense that the species' biological inheritance includes the potential to develop each gestural form and use it for a specific range of purposes. Moreover, the phylogenetic origin of many gestures is relatively old, since gestures are extensively shared between different genera in the great ape family. Acquisition of an adult repertoire is a process of first exploring the innate species potential for many gestures and then gradual restriction to a final (active) repertoire that is much smaller. No evidence of syntactic structure has yet been detected.

Medidas morfometricas foram tomadas, foi estimada abundância e feitas observacoes ecologicas para Sibon annulatus, S. argus, S. longifrenis e S. nebulatus em dois habitats neotropicais: Uma floresta pantanosa de baixada na Costa Rica e uma floresta de neblina no Panama. Quarenta e quatro e 58 serpentes adultas foram registradas na Costa Rica e no Panama, respectivamente. Diferencas morfologicas e na condicao corporal significativas foram minimas entre as especies para ambas as localidades. Sao discutidas as observacoes sobre alimentacao, reproducao, abundância, distribuicao e um registro de um novo tamanho maximo para S. annulatus.