Abstract: Facial features appear to be a prominent kinship cue for ascribing relatedness among human individuals. Although there is evidence that adults can detect kinship in unrelated and unfamiliar individual’s faces, it remains to be seen whether people already possess the ability when they are young. To further understand the development of this skill, we explored children’s ability to detect parent-offspring resemblance in unrelated and unfamiliar faces. To this end, we tested approximately 140 children, aged 5–11, in two photo-matching tasks. We used a procedure that asked them to match one neonate’s face to one of three adults’ faces (Task 1), or to match one adult’s face to one of three neonate’s faces (Task 2). Our findings reveal asymmetrical performance, depending on the tasks assigned (performance of Task 2 is stronger than for Task 1), and on the sex of individuals who made up the parent-offspring pair (male parents are better matched with neonates than female parents, and boys are better matched than girls). The picture that emerges from our study is, on one hand, that the ability to detect kinship is already present at the age of five but continues to improve as one gets older, and on the other, that perception of parent-offspring facial resemblance varies according to the appraisers’ characteristics.

Abstract: Great ape gestural communication is known to be intentional, elaborate and flexible; yet there is controversy over the best interpretation of the system and how gestures are acquired, perhaps because most studies have been made in restricted, captive settings. Here, we report the first systematic analysis of gesture in a population of wild chimpanzees. Over 266 days of observation, we recorded 4,397 cases of intentional gesture use in the Sonso community, Budongo, Uganda. We describe 66 distinct gesture types: this estimate appears close to asymptote, and the Sonso repertoire includes most gestures described informally at other sites. Differences in repertoire were noted between individuals and age classes, but in both cases, the measured repertoire size was predicted by the time subjects were observed gesturing. No idiosyncratic usages were found, i.e. no gesture type was used only by one individual. No support was found for the idea that gestures are acquired by ‘ontogenetic ritualization’ from originally effective actions; moreover, in detailed analyses of two gestures, action elements composing the gestures did not closely match those of the presumed original actions. Rather, chimpanzee gestures are species-typical; indeed, many are ‘family-typical’, because gesture types recorded in gorillas, orangutans and chimpanzee overlap extensively, with 24 gestures recorded in all three genera. Nevertheless, chimpanzee gestures are used flexibly across a range of contexts and show clear adjustment to audience (e.g. silent gestures for attentive targets, contact gestures for inattentive ones). Such highly intentional use of a species-typical repertoire raises intriguing questions for the evolution of advanced communication.

Abstract: In apes, four criteria are set to explore referential and intentional communication: (1) successive visual orienting between a partner and distant targets, (2) the presence of apparent attention-getting behaviours, (3) the requirement of an audience to exhibit the behaviours, and (4) the influence of the direction of attention of an observer on the behaviours. The present study aimed at identifying these criteria in behaviours used by dogs in communicative episodes with their owner when their toy is out of reach, i.e. gaze at a hidden target or at the owner, gaze alternation between a hidden target and the owner, vocalisations and contacts. In this study, an additional variable was analysed: the position of the dog in relation to the location of the target. Dogs witnessed the hiding of a favourite toy, in a place where they could not get access to. We analysed how dogs engaged in communicative deictic behaviours in the presence of their owner; four heights of the target were tested. To control for the motivational effects of the toy on the dogs’ behaviour and for the referential nature of the behaviours, observations were staged where only the toy or only the owner was present, for one of the four heights. The results show that gazing at the container and gaze alternation were used as functionally referential and intentional communicative behaviours. Behavioural patterns of dog position, the new variable, fulfilled the operational criteria for functionally referential behaviour and a subset of operational criteria for intentional communication: the dogs used their own position as a local enhancement signal. Finally, our results suggest that the dogs gazed at their owner at optimal locations in the experimental area, with respect to the target height and their owner’s (or their own) line of gaze.

Abstract: While viewing faces, human adults often demonstrate a natural gaze bias towards the left visual field, that is, the right side of the viewee’s face is often inspected first and for longer periods. Using a preferential looking paradigm, we demonstrate that this bias is neither uniquely human nor limited to primates, and provide evidence to help elucidate its biological function within a broader social cognitive framework. We observed that 6-month-old infants showed a wider tendency for left gaze preference towards objects and faces of different species and orientation, while in adults the bias appears only towards upright human faces. Rhesus monkeys showed a left gaze bias towards upright human and monkey faces, but not towards inverted faces. Domestic dogs, however, only demonstrated a left gaze bias towards human faces, but not towards monkey or dog faces, nor to inanimate object images. Our findings suggest that face- and species-sensitive gaze asymmetry is more widespread in the animal kingdom than previously recognised, is not constrained by attentional or scanning bias, and could be shaped by experience to develop adaptive behavioural significance.

Abstract: The study set out to examine whether the cerebral hemispheres differ in their ability to regulate cortisol secretion during emotion-related situations. One hundred twenty-three adult subjects were shown either an emotionally aversive or a neutral film in the left or right hemisphere by means of a technique for lateralizing visual input that allows prolonged viewing while permitting free ocular scanning. The film-related changes of cortisol secretion were determined by salivary cortisol radioimmunoassay. Right hemispheric viewing of the emotionally aversive film resulted in a significantly higher increase of cortisol secretion than left hemispheric viewing of the same film. No such differences were observed with respect to the neutral film. Comparing the effects of the two films separately for each hemisphere revealed that only the right hemisphere was able to respond neuroendocrinologically in a different manner to the emotional and the neutral film. Therefore, it is concluded that cortical regulation of cortisol secretion in emotion-related situations is under primary control of the right hemisphere. The potential implications of asymmetric control of cortisol secretion with respect to the pathogenesis of psychosomatic and immunological disorders are discussed.