The expression of empathy in human's closest relatives, bonobos and chimpanzees: current and future directions.

Empathy is a complex, multi-dimensional capacity that facilitates the sharing and understanding of others' emotions. As our closest living relatives, bonobos (Pan paniscus) and chimpanzees (P. troglodytes) provide an opportunity to explore the origins of hominin social cognition, including empathy. Despite certain assumptions that bonobos and chimpanzees may differ empathically, these species appear to overlap considerably in certain socio-emotional responses related to empathy. However, few studies have systematically tested for species variation in Pan empathic or socio-emotional tendencies. To address this, we synthesise the growing literature on Pan empathy to inform our understanding of the selection pressures that may underlie the evolution of hominin empathy, and its expression in our last common ancestor. As bonobos and chimpanzees show overlaps in their expression of complex socio-emotional phenomena such as empathy, we propose that group comparisons may be as or more meaningful than species comparisons when it comes to understanding the evolutionary pressures for such behaviour. Furthermore, key differences, such as how humans and Pan communicate, appear to distinguish how we experience empathy compared to our closest living relatives.

Females undergo selection too.

Extending Campbell's (1999) staying alive theory (SAT) beyond aggression, we reviewed evidence that females are more self-protective than males. Many commentators provided additional supporting data. Sex differences in life-history adaptations, in the optimal relation between survival and reproduction, and in the mechanisms underlying trade-offs involved with self-protection remain important topics with numerous opportunities for improved understanding.

Self-protection as an adaptive female strategy.

Many male traits are well explained by sexual selection theory as adaptations to mating competition and mate choice, whereas no unifying theory explains traits expressed more in females. Anne Campbell's "staying alive" theory proposed that human females produce stronger self-protective reactions than males to aggressive threats because self-protection tends to have higher fitness value for females than males. We examined whether Campbell's theory has more general applicability by considering whether human females respond with greater self-protectiveness than males to other threats beyond aggression. We searched the literature for physiological, behavioral, and emotional responses to major physical and social threats, and found consistent support for females' responding with greater self-protectiveness than males. Females mount stronger immune responses to many pathogens; experience a lower threshold to detect, and lesser tolerance of, pain; awaken more frequently at night; express greater concern about physically dangerous stimuli; exert more effort to avoid social conflicts; exhibit a personality style more focused on life's dangers; react to threats with greater fear, disgust, and sadness; and develop more threat-based clinical conditions than males. Our findings suggest that in relation to threat, human females have relatively heightened protective reactions compared to males. The pervasiveness of this result across multiple domains suggests that general mechanisms might exist underlying females' unique adaptations. An understanding of such processes would enhance knowledge of female health and well-being.

The Study That Made Rats Jump for Joy, and Then Killed Them: The Gap between Knowledge and Practice Widens When Scientists Fail to Engage with the Ethical Implications of Their Own Work.

Much contemporary behavioral science stops short of considering the ethical implications of its own findings. This generates a contradiction between methods and discoveries, and hinders translation between updated scientific evidence for animal sentience and corresponding political and legal changes. A recent and particularly illustrative example in rodents is described here.

Jealous Behavior in Chimpanzees Elicited by Social Intruders.

Despite increasing interest in animal emotions, jealousy has rarely been directly addressed in comparative research, except for studies of human-pet interactions. Jealous behavior emerges when a valuable social bond is threatened by a third-party, prompting aggression or intervention attempts to direct the partner's attention away from the rival. Emotional reactions that protect relationships are expected in species in which social relationships are important for fitness, including primates. Previous primate studies have alluded to this ultimate function, but never explicitly tested predictions corresponding to a proximate jealousy mechanism. We demonstrate jealous behavior in a long-established colony of chimpanzees (N = 17) during a socially disruptive period due to group introductions, which provided an ideal experimental opportunity to test predictions of a jealousy hypothesis. Specifically, we found that negative reactions (agonism and intervention attempts) towards social closeness between two groupmates were generally more common when the aggressor/intervener had a valuable relationship to one (as compared with both or neither) of the dyad's members, indicating that the other partner represented a potential social rival. In line with this suggestion, we found that negative reactions most often targeted dyads containing newly introduced individuals, especially when the social conditions for jealousy were met, and in particular during the socially unstable introduction period. Results underscore the potential adaptive role of jealousy in protecting fitness-enhancing relationships from social interlopers, by extension indicating that this emotion likely evolved in diverse animal societies.

Do chimpanzees (Pan troglodytes) console a bereaved mother?

Comparative thanatology encompasses the study of death-related responses in non-human animals and aspires to elucidate the evolutionary origins of human behavior in the context of death. Many reports have revealed that humans are not the only species affected by the death of group members. Non-human primates in particular show behaviors such as congregating around the deceased, carrying the corpse for prolonged periods of time (predominantly mothers carrying dead infants), and inspecting the corpse for signs of life. Here, we extend the focus on death-related responses in non-human animals by exploring whether chimpanzees are inclined to console the bereaved: the individual(s) most closely associated with the deceased. We report a case in which a chimpanzee (Pan troglodytes) mother experienced the loss of her fully developed infant (presumed stillborn). Using observational data to compare the group members' behavior before and after the death, we found that a substantial number of group members selectively increased their affiliative expressions toward the bereaved mother. Moreover, on the day of the death, we observed heightened expressions of species-typical reassurance behaviors toward the bereaved mother. After ruling out several alternative explanations, we propose that many of the chimpanzees consoled the bereaved mother by means of affiliative and selective empathetic expressions.

Long-term consistency in chimpanzee consolation behaviour reflects empathetic personalities.

In contrast to a wealth of human studies, little is known about the ontogeny and consistency of empathy-related capacities in other species. Consolation-post-conflict affiliation from uninvolved bystanders to distressed others-is a suggested marker of empathetic concern in non-human animals. Using longitudinal data comprising nearly a decade of observations on over 3000 conflict interactions in 44 chimpanzees (Pan troglodytes), we provide evidence for relatively stable individual differences in consolation behaviour. Across development, individuals consistently differ from one another in this trait, with higher consolatory tendencies predicting better social integration, a sign of social competence. Further, similar to recent results in other ape species, but in contrast to many human self-reported findings, older chimpanzees are less likely to console than are younger individuals. Overall, given the link between consolation and empathy, these findings help elucidate the development of individual socio-cognitive and -emotional abilities in one of our closest relatives.Non-human animals are known to exhibit behaviours suggestive of empathy, but the development and maintenance of these traits is unexplored. Here, Webb and colleagues quantify individual consolation tendencies over 10 years across two chimpanzee groups and show evidence of consistent 'empathetic personalities'.

Stepping forward together: Could walking facilitate interpersonal conflict resolution?

Walking has myriad benefits for the mind, most of which have traditionally been explored and explained at the individual level of analysis. Much less empirical work has examined how walking with a partner might benefit social processes. One such process is conflict resolution-a field of psychology in which movement is inherent not only in recent theory and research, but also in colloquial language (e.g., "moving on"). In this article, we unify work from various fields pointing to the idea that walking together can facilitate both the intra- and interpersonal pathways to conflict resolution. Intrapersonally, walking supports various psychological mechanisms for reconciliation, including creativity, locomotion motivation, and embodied notions of forward progress. Both alone and in combination with its effects on mood and stress, walking can encourage individual mindsets conducive to resolving conflict (e.g., divergent thinking). Interpersonally, walking can allow partners to reap the cognitive, affective, and behavioral advantages of synchronous movement, such as increased positive rapport, empathy, and prosociality. Walking partners naturally adopt cooperative (as opposed to competitive) postural stances, experience shared attention, and can benefit from discussions in novel environments. Overall, despite its prevalence in conflict resolution theory, little is known about how movement influences conflict resolution practice. Such knowledge has direct implications for a range of psychological questions and approaches within negotiation and alternative mediation techniques, clinical settings, and the study of close relationships. (PsycINFO Database Record

Moving on or digging deeper: Regulatory mode and interpersonal conflict resolution.

Conflict resolution, in its most basic sense, requires movement and change between opposing motivational states. Although scholars and practitioners have long acknowledged this point, research has yet to investigate whether individual differences in the motivation for movement from state-to-state influence conflict resolution processes. Regulatory Mode Theory (RMT) describes this fundamental motivation as locomotion. RMT simultaneously describes an orthogonal motivational emphasis on assessment, a tendency for critical evaluation and comparison. We argue that this tendency, in the absence of a stronger motivation for locomotion, can obstruct peoples' propensity to reconcile. Five studies, using diverse measures and methods, found that the predominance of an individual's locomotion over assessment facilitates interpersonal conflict resolution. The first two studies present participants with hypothetical conflict scenarios to examine how chronic (Study 1) and experimentally induced (Study 2) individual differences in locomotion predominance influence the motivation to reconcile. The next two studies investigate this relation by way of participants' own conflict experiences, both through essay recall of previous conflict events (Study 3) and verbal narratives of ongoing conflict issues (Study 4). We then explore this association in the context of real-world conflict discussions between roommates (Study 5). Lastly, we examine results across these studies meta-analytically (Study 6). Overall, locomotion and assessment can inform lay theories of individual variation in the motivation to "move on" or "dig deeper" in conflict situations. We conclude by emphasizing the importance of using RMT to go beyond instrumental approaches to conflict resolution to understand fundamental individual motivations underlying its occurrence. (PsycINFO Database Record

An inversion effect modified by expertise in capuchin monkeys.

The face inversion effect may be defined as the general impairment in recognition that occurs when faces are rotated 180°. This phenomenon seems particularly strong for faces as opposed to other objects and is often used as a marker of a specialized face-processing mechanism. Four brown capuchin monkeys (Cebus apella) were tested on their ability to discriminate several classes of facial and non-facial stimuli presented in both their upright and inverted orientations in an oddity task. Results revealed significantly better performance on upright than inverted presentations of capuchin and human face stimuli, but not on chimpanzee faces or automobiles. These data support previous studies in humans and other primates suggesting that the inversion effect occurs for stimuli for which subjects have developed an expertise.