Introduction

Within social philosophy, consolation is seen as a fundamental human achievement [1]. Consolation, in this view, soothes anxiety and our existential vulnerability, and draws on a shared sense of humanity, empathy, trust and perspective-taking. Scholarship on consolation dates back to the Greco-Roman world, and unlike mere empathic perspective-taking that does not necessitate action, consolation requires action in response to the recognition of the plight of the other [2].

While the extensive philosophical literature on consolation is extensive, few observational or ethological studies are available on human consolation in naturalistic settings. This paucity likely reflects the difficulty of carrying out unobtrusive and systematic observation of human behavior in natural conflict [3]. Here we introduce surveillance camera footage as a new method to systematically measure post-aggression consolation in adult humans. Specifically, we analyzed the immediate aftermath of nonfatal robberies to look for adult human consolation. Surveillance camera footage offers a unique and ethically sound way of studying adult behavior in high-danger contexts [4].

In nonhuman primates, consolation was first observed in chimpanzees (Pan troglodytes). Consolation was termed as such because it visibly reduced distress in victims of aggression [5, 6] and subsequent research has confirmed this function [6, 7]. Behaviorally, consolation in nonhuman primates is commonly defined as interactions in which an uninvolved bystander initiates friendly contact with a recent recipient of aggression [8]. Consolation so defined is a highly replicable finding in chimpanzee populations [7, 9, 10], and has since been further documented in bonobos (Pan paniscus) [11, 12], mountain gorillas (Gorilla beringei beringei) [13], Western lowland gorillas (Gorilla gorilla gorilla) [14], and Tonkean macaques (Macaca tonkeana) [15]. In monkeys, bystanders have also been observed to offer friendly contact when solicited to do so by victims (e.g., Cebus apella) [16, 17]. As later research showed, the differentiation between (a) consolation initiated by the bystander (“consolation proper”), and (b) friendly bystander contact solicited by recipients of aggression, is important to understand the functional significance as well as the cognitive and emotional implications of the behavior [18]. Indicative of convergent evolution, consolation, as defined for nonhuman primates, has now also been observed in non-primate species such as canids, corvids, rodents and elephants [19].

Research on post-aggression consolation in humans has mainly focused on children from various cultures [20–22]. For example, Japanese children as young as 4 years of age offered consolation to victims of peer aggression. The frequency of this consolation increased rapidly between 4 and 5 years of age, most likely a reflection of developing socio-cognitive skills such as the ability to attribute mental states to others (“Theory of Mind”), and to understand that another’s point of view about an issue may contrast with one’s own [23, 24]. In this context, consolation in human adults can be seen as an empathy-related behavior that involves sharing another’s distress via emotional contagion, combined with sympathizing and perspective-taking [25–27].

Almost three decades ago, in 1989, de Waal called for more naturalistic studies on human adults so as to overcome the view that the human-nonhuman primate comparisons simply show that “other primates are mentally like human children” [28]. Here we compare post-aggression consolation in human adults with post-aggression consolation that prior research has identified in adult chimpanzees. Through this comparison with our evolutionary closest kin, we shed light on the mental processes involved in post-aggression consolation across human and non-human primates [29]. Such comparison is in agreement with the principle of evolutionary parsimony advocated by de Waal, suggesting that if closely related species behave similarly, then the underlying mental processes are presumably similar too [29].

A growing body of research across chimpanzee populations in varied social conditions shows how bystander affiliation may serve vital peacemaking and peacekeeping functions. For example, chimpanzee bystander affiliation can appease aggressors—especially if the bystander has a close relationship with the aggressor [8]—which can protect bystanders against redirected aggression [30]. Chimpanzees also offer consolation to victims of aggression, often by hugging and kissing the victim. It can be assumed that these different types of bystander affiliation and the functions that they serve rely on different social and individual motivations [31].

Post-aggression consolation in chimpanzees is promoted by social closeness [9, 32, 33]. Although several earlier studies did not find evidence associating age and sex with the likelihood of providing consolation [6, 34, 35], a recent study that draws on data from an exceptionally large sample of spontaneous consolation in chimpanzees, offers compelling evidence that female individuals are more likely to provide post-aggression consolation than males [9]. Given that social closeness is known to facilitate empathy in both humans and other animals and that females are generally more empathic than males, these findings are consistent with an empathy explanation [36].

We analyzed the video-recorded behavior of 249 individuals who were present in the aftermath of 22 commercial robberies, immediately after the offenders had left the scene. We investigated whether and how providing and receiving consolation were affected by social closeness and gender. Specifically, as documented in chimpanzees and predicted by the empathy explanation, we hypothesized that consolation is promoted by social closeness and that females are more likely than males to provide consolation.

According to theory, and supported by empirical findings in ethology and in the social sciences, we hypothesized that consolation might be further facilitated by additional factors. First, based on the homophily principle that similarity breeds connection [37], we conjectured that consolation is more likely between individuals that are similar in terms of ethnicity and age; two of the factors that create the strongest divides in our personal environments [37]. This hypothesis is supported by findings demonstrating that empathic response is amplified by similarity and that individuals are more likely to help distressed others that are similar to themselves in terms of age and ethnicity [38–40].

Second, a comprehensive literature in social psychology has studied the conditions under which human bystanders respond to the needs of victims in emergency situations. A recurring finding is the 'bystander effect', the phenomenon that individual bystanders are less likely to intervene with increasing numbers of other bystanders present [41, 42]. The bystander effect is typically ascribed to a psychological process by which the presence of other bystanders diffuses the responsibility for helping. To test for the bystander effect, we measured the total numbers of individuals present in the aftermath of the robbery.

Because individuals who have better opportunities to respond to distressed victims are reportedly more likely to respond [42], and because physical proximity between individuals has been demonstrated to facilitate consolation among human children [23], we measured the physical distance between all pairs of individuals at the start of the robbery aftermath. We hypothesized that consolation is more likely to occur when individuals are in closer proximity to each other.

A third theoretical framework from which we draw is the aversive-arousal reduction hypothesis [43]. It proposes that the empathic arousal evoked by witnessing the distress of another person is an unpleasant feeling, which can be alleviated by victim helping. As human bystander research suggests that people are more likely to help distressed victims in high-danger compared to low-danger situations [42], we also measured the degree of threat that potential recipients of consolation had been exposed to during the robbery. We hypothesized that a higher level of threat exposure would make an individual more likely to receive consolation from others. In addition, but more tentatively, we hypothesized that arousal itself, independent of its origin, is reduced by providing consolation. To examine this possibility, we also included the degree of threat that potential providers of consolation had been exposed to during the robbery. This allowed us to test whether the individuals most severely affected by threat during the robbery would be more likely to console others than individuals less affected.

Finally, sociological theory and cross-cultural empirical studies on gender suggest that social norms depict females to be more vulnerable, and hence more eligible for helping behavior than males [44]—particularly in dangerous situations [45]. It has also been demonstrated that it is more socially acceptable to touch women than men [46]. To investigate the validity of these findings–which point towards females as more likely recipients of consolation than males—we included the gender of potential consolation recipients as a variable of interest.

Based on the premise that bystanders are in a state of lower emotional involvement than victims, all prior empirical studies on post-aggression consolation have assumed that victims and bystanders are discrete categories. This implies that only bystanders and not victims of violence can provide consolation, and that only victims and not bystanders can receive it. However, distinctions between victims and bystanders in robberies can be fluid, and emotional involvement need not necessarily differentiate strongly between those who have been exposed to aggression firsthand (victims) and those who have been exposed by proxy (bystanders). For this reason, we did not label the individuals as either victims or bystanders, but instead measured for each individual the extent to which they had been subjected to threat during the preceding robbery. The observed level of threat directed towards the individual was thus included as a variable. To reiterate, this was not used to create a dichotomy between victims and bystanders.

In addition, we did not make any assumptions on who could console whom. We considered all dyads in both directions as potential consolation opportunities. This approach made it possible to analyze multiple instances of consolation between multiple individuals involved in the same incident. Simultaneously, this allowed the observation of unexpected behavioral patterns. For example, it allowed us to include in the analysis potential cases in which an individual who experienced a brutal attack could console an individual who only witnessed the event. Further details of the analytical approach are provided in the ‘Materials and methods’ section.

Consolation was defined as affiliative physical contact, including not only ‘hugging’, but also gentle touching of the target’s head, upper body, arms or hands (see S1–S3 Tables for the codesheets that were used).

Materials and methods

Results

The binary response variable in our analysis is whether consolation is provided by one individual to another. This variable is observed for every pairwise combination of individuals in the aftermath of the same robbery. This setup allows for the observation of a variety of patterns, including a single individual providing consolation to multiple others, and a single individual being consoled by multiple others. Consolation was not observed in the aftermath of 4 (18.2%) of the 22 robberies. In the remaining 18 cases, at least one person consoled at least one other person. Of the 249 individuals that were observed in the aftermath of the 22 robberies, 38 (15.3%) provided consolation to others, and 24 (9.6%) received consolation from others.

As our interest in consolation behavior focused on who is providing consolation to whom, we analyzed the data at the dyadic level. For each robbery i we considered all possible N_i × (N_i-1) (directed) pairs of individuals present in its aftermath, where N_i is the number of individuals present in the aftermath of robbery i. The 249 individuals in 22 robberies included 3710 dyads. Using a logit model, we assessed which factors made consolation less or more likely to take place between the two members of a pair. Table 1 displays the roles of the four most significant factors.

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Table 1. Logit analysis of consolation among 3680 dyads⁴. Quadratic assignment procedure.

https://doi.org/10.1371/journal.pone.0177725.t001

Social closeness predicted consolation. When both potential provider and potential recipient were employees of the same business (and thus presumably familiar having shared common experiences), the odds of consolation were 7.4 times greater than when either one or both of the dyad, were customers. Females were more likely to provide consolation than males. The odds of consolation were 2.7 times greater when the potential provider was female. Although some males provided consolation, females were more likely to offer it. Consolation was more likely to be provided to individuals exposed to high levels of threat (i.e., exposure to physical force or weapon threat). Victimization of a prospective recipient during the preceding robbery was the most important factor predicting consolation. For victims of either force or threat with a weapon, the odds of receiving consolation increased by a factor of 36.3.

To account for an unresponsive bystander effect due to a diffusion of responsibility [41], the model included the total number of individuals present in the robbery aftermath. Contrary to the hypothesized bystander effect, the odds of being consoled increased by two percent for every additional individual present in the aftermath of the robbery. To assess whether consolation is facilitated by opportunity, a model was estimated that included the physical distance between dyad members, measured by whether the pair were more than 2 meters apart at the start of the robbery aftermath. The results, reported in S4 Table, demonstrate that physical distance has no significant effect on the likelihood of providing consolation.

Although it has been argued that bystanders tend to help others in order to reduce their own stress [57], the results presented in S5 Table demonstrate no significant relationship between exposure to weapon threat or physical force and the likeliness of providing consolation. High levels of threat entitled individuals to receive consolation but did not make them more likely to provide it. Moreover, we did not find a relationship between receiving consolation and gender (see S6 Table). Exposure to weapon threat or physical force, not gender, determined whether individuals were eligible to receive consolation. Male victims were as likely as female victims to be touched by female consolers.

Based on the homophily principle, we tested whether consolation was more likely between individuals similar in terms of age and ethnicity. Individuals were coded as similar in terms of age if their estimated ages differed by less than 10 years (dyads with missing age estimates were removed from the analysis). Individuals were coded as ethnically similar if they were estimated to belong to the same ethnic group (dyads with missing ethnicity estimates were removed from the analysis and individuals in the ‘other’ category were never coded as ethnically similar to anyone). The outcomes of these models are displayed in S7 Table, and show that similarity based on age or ethnicity was unrelated to the probability of consolation.

Finally, all potentially relevant factors measured were included simultaneously in a single model. The results are displayed in Table 2, and again confirm that consolation is significantly more likely to be provided amongst affiliated individuals (i.e., employees), to be given by females, to be received by victims of threat and force (rather than received by bystanders) and to be provided when more individuals are present. All other potential factors were non-significant.

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Table 2. Logit analysis of consolation among 3364 dyads⁴. Quadratic assignment procedure.

https://doi.org/10.1371/journal.pone.0177725.t002

Discussion

Contemporary views in primatology consider empathic perspective-taking: putting oneself emotionally and cognitively into the other’s shoes, to be an integral component of human and nonhuman primate consolation [58]. According to this view, a chimpanzee bystander who offers consolation most likely acts on empathic perspective-taking, while a monkey bystander that offers comfort after being solicited to do so by a victim does not.

In the present study we showed that among human adults, as has been found in studies with chimpanzees, social closeness increased the likelihood of post-aggression consolation. Our study thus provides additional evidence that pro-social behavior is more likely among people who are familiar [27]. It might be the case that it is easier for familiars to interpret each other’s signals of distress [59]. Consolation may also be a way of establishing relationships or strengthening existing ones [60]. Note that unlike measures of social closeness in other studies, which are usually based on observed behavior that could indicate close affiliation (e.g., grooming, food-sharing), our measure of social closeness was based on the assumption that employees know each other and share similar experiences. This assumption does not typically hold for customers, nor for employees and customers.

In line with recent evidence on consolation in chimpanzees [9], we also found that females were more likely to console than males. This supports the notion that females are more prone to empathy-driven pro-social behavior than males [61–64]. One explanation for this finding is that females may be more sensitive to the emotional signals of others [65] due to maternal functions, social upbringing [66, 67] and cultural expectations [68]. Across cultures, it is also more acceptable for females than males to communicate through touching [46]. Taken together, the above results are consistent with an empathy-based explanation of differences in consolation, and suggest homologous mental processes of empathy in humans and chimpanzees.

Interestingly, females were not more likely to receive consolation than males. This challenges previous findings suggesting differential gender roles, particularly in dangerous situations [44, 45]. It also challenges studies showing that it is more socially acceptable to touch women than men [46]. Furthermore, our findings showed that for a given pair of individuals, the likelihood of consolation increased with the number of other individuals present. This contradicts the hypothesized bystander effect and confirms recent evidence that violence may diminish the bystander effect [42] or even reverse it [4]. Unlike prior findings on consolation in bonobos [12], our findings demonstrate that the physical distance between two individuals does not affect the probability of consolation. This suggests that providing consolation depends more on motivation than on opportunity.

Subjects who had been confronted with physical force or threats with weapons were much more likely to receive consolation than subjects who had experienced lower levels of threat. This shows the importance of considering threat levels while studying consolation, potentially also in studies of non-human apes.

The finding that individuals who had been subjected to physical violence or threat of violence during the robbery were not more likely to provide consolation to others, suggests that consolation was not primarily provided as a means of reducing one’s own stress; as the aversive-arousal reduction hypothesis would predict. Rather consolation was provided as a means of reducing the stress of others, thus supporting the empathy hypothesis. Future studies need to investigate whether consolation in adults also exists in low intensity conflict, and whether it follows the same patterns found here in high intensity conflicts.

Among humans, a sense of shared humanity is believed to mediate consolation [2]. Does a shared sense of ‘chimpness’ mediate consolation in adult chimpanzees? At the perceptual level, it appears that chimpanzees share such a common chimpness. Chimpanzees demonstrate self-recognition by passing the mirror self-recognition test [69] and exhibit self-awareness by distinguishing in real time an object that is under their control from one that is not [70]. Chimpanzees discriminate chimpanzee faces from the faces of other primate species, recognize kin relations by looking at conspecific faces, and tell apart and categorize expressions that are modelled by the faces of other chimpanzees [71]. Fights arouse special attention in chimpanzees. Controlled video tests of emotional scenes show that chimpanzees pay more attention to conspecific aggressive scenes than to other social situations, including play and general excitement [72].

Comparative research across species can offer clues about how species-typical social experiences and perception may be a factor in consolation. Delineating the roots and components of consolation through comparative research reminds us that the differences in the mental lives of animals are one of degree and not of kind. This ought to have implications for the practices of behavioral sciences and for the way we attend to animals other than humans.

Supporting information

Acknowledgments

CCTV footage was made accessible by the police forces of Amsterdam and Rotterdam, The Netherlands. The video materials were coded by Tom de Vries and Floris Mosselman. The Research and Documentation Centre (WODC) of the Netherlands Ministry of Security and Justice supported the use of Observer XT software.