Humans are extraordinary prosocial beings. No other Great Ape species invests a comparable amount of time and resources into building, maintaining, and repairing social relationships. The degree to which small-scale communities and large-scale societies embrace the human capacity for prosociality and capitalise on human-unique forms of cooperation is variable. The cross-cultural constant, however, is that each individual child undergoes a critical period of prosocial development in the first four years of life. During this period children’s emotions undergo a culture-specific transformation through children’s interactions with adults, siblings, and same-age peers. Studying how emotions shape young children’s social interactions, how they allow children to maintain and repair social relationships, is the developmental psychologist’s study of the psychological origins of human prosociality. This thesis is about studying examples of such so-called prosocial emotions. The main question of the current thesis is: How do emotions regulate children’s social inter- actions and relationships in early ontogeny? Addressing this question requires the assessment of both the internal mechanisms (attention and physiological arousal) as well as the expression (in behaviour or body language) of emotions in young children’s social interactions. At first, I provide a theoretical basis for studying the regulatory function of prosocial emotions in the first four years of children’s development. I suggest that children’s developing prosociality progresses through two distinct phases, one which shapes their attention and physiological arousal to others’ needs in the first two years of life, and subsequently a second phase during which children’s prosocial behaviour emerges and is increasingly regulated by emotions. In contrast to previous work, such a study of emotions as underlying early prosocial development requires broadening the suite of methods through which emotions are objectively measurable and interpretable. The first research aim was to study the development of children’s attention and arousal in response to others’ needs. We found that prosocial attention is a stable phenomenon from toddlerhood through school-age. In both a western and non-western culture, children anticipated how others are best helped. In a clinical comparison study, we found that this anticipatory response was blunted in children with an autism spectrum diagnosis. Young children’s prosocial orientation was not limited to helping contexts but encompassed other domains. Toddlers understood others’ desires and anticipated how those were best met. We further found that two-year toddlers were attentive to same-age peers’ needs and helped a same-age peer in sim- ilar ways and to a similar degree as has been previously reported in studies with child-adult interactions. We further found that toddlers’ attention to others’ needs was not contingent on explicit requests for help. Rather toddlers helped an adult even if helping was anonymous suggesting that toddlers did not help to interact with a competent adult partner. Finally, in a comparative study, we found chimpanzees’ underlying motivation to provide help to be different from that previously documented in young children. Chimpanzees were fastest to complete an action if this resulted in a conspecific’s need being fulfilled but, in contrast to young children, chimpanzees were motivated to carry out the behaviour themselves (which was not the case in non-helping control scenarios). Together, this indicates that a young chil- dren’s prosocial orientation develops during and persists beyond the first two years of life, thus laying the foundation for children’s prosocial behaviour. The second research aim was to study how children’s attention to others’ needs relates to their actual prosocial behaviour. In a first, comparative, study we found that young children regulated their prosocial behaviour more than chimpanzees. Both 3-year-old children and chimpanzees helped others, but children were more strongly motivated to help paternalistically by correcting dysfunctional requests for help that did not align with the requester’s actual need. The implication of these findings is that chimpanzees’ helping is more motivated by concerns to ’get credit’ and comply with others’ request for help whereas children’s helping is based on a, sometimes even paternalistic, concern to see others being helped. In a separate series of studies we developed experimental paradigms that allowed us to mea- sure the underlying emotions through changes in both internal arousal as well as overt body expressions. We found that changes in children’s physiological arousal were predictive of their subsequent helping behaviour. We further studied the function of guilt and gratitude in regulating two- and three-year-olds’ prosocial behaviour. Children’s intrinsic motivation to help an adult changed when they had accidentally caused the adult harm (guilt) or when the adult had previously helped them (gratitude). Specifically, guilt- and gratitude-provoking situations motivated young children to actively provide help. In contrast, and replicating previous work, under conditions without invoked guilt or gratitude, children’s motivation was to see that individual being helped (irrespective of whether they themselves or another adult provided the help). In a separate study we investigated children’s positive emotions, expressed in elevated upper-body posture, resulting from their successful helping behaviour. Children at the age of two years showed a similarly elevated body posture after completing a goal for themselves and after completing an adult’s goal whereas no such elevation was observed when children’s actions did not benefit anyone. Together these findings suggest that emotions invoked in their interactions with others in turn influence children’s motivation to interact, thus serving a regulatory function to repair (guilt) and maintain (gratitude) children’s social relationships. This successful navigation of the social world may contribute to children’s own emotional well-being. In sum, the current thesis explored the developmental origins of prosociality focusing on prosocial emotions that allow already young children to build and maintain functional relationships with adults and peers. The first four years of life give rise to prosocial emotions that critically shape children’s social interactions toward cooperative ends. Together, the re- search presented here adds to our knowledge of the deep ontogenetic roots of human-unique prosociality.:1 Executive summary 1 2 Introduction and background 3 2.1 Children’s prosocial attention and interactions.................... 6 2.2 The regulatory social function of children’s emotions . . . . . . . . . . . . . . . . 8 2.2.1 Children’s emotional response to seeing others needing help . . . . . . . 8 2.2.2 Children’s emotional response to seeing others being helped . . . . . . . 9 3 Theoretical framework and research programs 11 3.1 Revealing the foundation of human prosociality (Theoretical paper 1) . . . . . 11 3.1.1 Precursors and mechanisms........................... 12 3.1.2 Social groups & interaction partners...................... 13 3.1.3 The self in social relationships ......................... 13 3.1.4 The long reach of early development ..................... 14 3.2 ResearchPrograms .................................... 15 3.2.1 Prosocial attention and interactions ...................... 16 3.2.2 The regulatory social function of emotions . . . . . . . . . . . . . . . . . . 17 4 Empirical studies 21 4.1 The development of prosocial attention across two cultures (Study 1) . . . . . . 21 4.1.1 Abstract ...................................... 21 4.1.2 Introduction.................................... 21 4.1.3 Materials and methods.............................. 24 4.1.4 DataAnalysis................................... 26 4.1.5 Results....................................... 28 4.1.6 Discussion..................................... 31 4.2 Prosocial attention in children with an autism spectrum diagnosis (Study 2) . . 35 4.2.1 Abstract ...................................... 35 4.2.2 Introduction.................................... 35 4.2.3 Methods...................................... 38 4.2.4 Data analysis ................................... 40 4.2.5 Results....................................... 44 4.2.6 Discussion..................................... 46 4.3 Desire understanding in 2-year-old children: An eye-tracking study (Study 3) . 50 4.3.1 Abstract ...................................... 50 4.3.2 Introduction.................................... 50 4.3.3 Methods...................................... 53 4.3.4 Results....................................... 57 4.3.5 Discussion..................................... 61 4.4 Toddlers help anonymously (Study4)......................... 65 4.4.1 Abstract ...................................... 65 4.4.2 Introduction.................................... 65 4.4.3 Study1....................................... 66 4.4.4 Study1: Methods................................. 66 4.4.5 Study1: Results.................................. 70 4.4.6 Study1: Discussion................................ 70 4.4.7 Study2....................................... 72 4.4.8 Study2: Method ................................. 72 4.4.9 Study2: Results.................................. 74 4.4.10 General discussion ................................ 75 4.5 Toddlers help a peer (Study5) ............................. 79 4.5.1 Abstract ...................................... 79 4.5.2 Introduction.................................... 79 4.5.3 Method....................................... 81 4.5.4 Results....................................... 86 4.5.5 Discussion..................................... 89 4.6 Chimpanzees are motivated to help others - and to get credit (Study 6) . . . . . 93 4.6.1 Abstract ...................................... 93 4.6.2 Introduction.................................... 93 4.6.3 Study1....................................... 95 4.6.4 Results.......................................100 4.6.5 Study2.......................................102 4.6.6 Results.......................................103 4.6.7 General discussion ................................104 4.7 Chimpanzees comply with requests; Children fulfil others’ needs (Study 7) . . . 106 4.7.1 Abstract ......................................106 4.7.2 Introduction....................................106 4.7.3 General method..................................109 4.7.4 Study1.......................................111 4.7.5 Results.......................................115 4.7.6 Study2.......................................116 4.7.7 Results.......................................119 4.7.8 General discussion ................................119 4.8 Young children’s physiological arousal and their motivation to help (Study 8) . 123 4.8.1 Abstract ......................................123 4.8.2 Introduction....................................123 4.8.3 Methods......................................126 4.8.4 Data analysis ...................................128 4.8.5 Results.......................................130 4.8.6 Discussion.....................................131 4.9 Children’s intrinsic motivation to reconcile after accidental harm (Study 9) . . . 135 4.9.1 Abstract ......................................135 4.9.2 Introduction....................................135 4.9.3 General method..................................137 4.9.4 Study1.......................................142 4.9.5 Study1: Results and discussion ........................145 4.9.6 Study2.......................................146 4.9.7 Study2: Results..................................148 4.9.8 General discussion ................................149 4.10 Toddlers’ intrinsic motivation to return help to their benefactor (Study 10) . . . 152 4.10.1 Abstract ......................................152 4.10.2 Introduction....................................152 4.10.3 Study1:Methods.................................155 4.10.4 Study1:Results..................................161 4.10.5 Study1:Discussion................................163 4.10.6 Study2:Methods.................................164 4.10.7 General discussion ................................167 4.10.8 Conclusion.....................................170 4.11 The fulfillment of others’ needs elevates children’s body posture (Study 11) . . . 171 4.11.1 Abstract ......................................171 4.11.2 Introduction....................................171 4.11.3 Validation study .................................173 4.11.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 4.11.5 Study 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 4.11.6 Study1:Method .................................176 4.11.7 Study1:Results..................................181 4.11.8 Study1:Discussion................................183 4.11.9 Study 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 4.11.10 Study2:Method .................................185 4.11.11 Study 2: Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 4.11.12 General discussion ................................189 5 Integrative discussion and theoretical perspectives 193 5.1 Children’s prosocial attention and interactions . . . . . . . . . . . . . . . . . . . .194 5.1.1 Summary & conclusions.............................194 5.1.2 Future directions .................................195 5.2 Prosocial arousal in children (Theoretical paper 2) . . . . . . . . . . . . . . . .200 5.2.1 Abstract ......................................200 5.2.2 Introduction....................................200 5.2.3 The phenomenon and the debate........................201 5.2.4 Measuring prosocial arousal ..........................202 5.2.5 Children’s prosocial arousal and intrinsic motivation to help . . . . . . . 204 5.2.6 Looking ahead ..................................205 5.2.7 Conclusion.....................................207 5.3 The regulatory social function of children’s emotions . . . . . . . . . . . . . . . .207 5.3.1 Summary & conclusions.............................207 5.3.2 Future directions .................................208 5.4 The development of prosocial emotions (Theoretical paper 3) . . . . . . . . . . 211 5.4.1 Abstract ......................................211 5.4.2 Introduction....................................211 5.4.3 The prosocial functions of emotions......................212 5.4.4 General discussion and future directions . . . . . . . . . . . . . . . . . . .220 6 Bibliography 227 7 Declaration of originality 255 8 Contribution statement 257

Dans le règne animal, certaines espèces présentent une organisation en groupe complexe, permettant l’établissement d’interactions sociales plus ou moins élaborées entre les individus. Les comportements prosociaux, visant à améliorer le bien-être de l’autre, apparaissent préférentiellement entre animaux qui partagent une grande affinité ; ces comportements sont probablement favorisés par l’empathie, suggérant une prise en compte émotionnelle du partenaire. Les oiseaux, et particulièrement les corvidés et les psittacidés, se révèlent être d’excellents modèles pour étudier ce lien entre relation sociale et prise en compte de l’autre: ils forment des couples monogames sur le long terme au sein desquels une forte coopération existe. L’objectif de cette thèse est d’explorer comment le lien entre individus (familial, sexuel, amical) module les comportements prosociaux et empathiques. Les réactions des sujets sont évaluées via le partage de nourriture ou bien en observant une sensibilité accrue envers un congénère. Chez les perruches calopsittes (Nymphicus hollandicus), les oiseaux réagissent plus fortement au cri de détresse d’un oiseau préféré qu’au cri d’un autre congénère familier et les individus apparentés (frères et sœurs) partagent davantage la nourriture entre eux qu’avec les autres. Les perroquetsont tendance à être prosociaux mais la prise en compte de l’autre reste à confirmer. Les choucas des tours (Corvus monedula), placés dans une situation nouvelle avec un autre oiseau, passent plus de temps à proximité de leur partenaire sexuel que d’un autre oiseau de sexe opposé. Ces différents résultats suggèrent qu’un lien d’affinité existe entre les individus et qu’il façonne leurs comportements en termes de prosocialité et d’empathie. / In the animal kingdom some species form complex social groups in which elaborated relationships between individuals occur. Prosocial behaviors, i.e. actions that benefit others, preferentially occur between closely affiliated individuals and may be driven by empathy, the ability to identify and share the emotional states of others. Birds, particularly corvids and parrots, are excellent candidates for investigating the link between social relationship and other-regarding behavior. They are long-lived and form long-term monogamous pair-bonds in which a high level of cooperation is seen throughout the year. The aim of this thesis is to study how the nature of a relationship (sibling, mate or friend) can modulate prosocial behavior and its underlying emotions in parrots and a corvid species. The approach was to study food-sharing or behavioral reactions to stressful situations such as distress call playback or exposure to novel objects, in different social contexts. Cockatiels (Nymphicus hollandicus) reacted more to the distress calls of a closely affiliated partner than to those of a non-partner, and they preferably shared food with affiliated, related individuals. Different species of parrots preferentially chose a prosocial option over a selfish one, but it remains unclear whether they took the other’s perspective into account. Confronted with intimidating novel objects, jackdaws (Corvus monedula) spent more time in mutual proximity when paired with their mate than when with a familiar opposite-sex non-partner. However, they were not bolder when accompanied by their mate compared to a non-partner. These results suggest that an emotional link exists between affiliated individuals and that this special bond drives their prosocial and empathic behavioral responses. / Im Tierreich gibt es Arten mit komplexer Gruppenstruktur, in denen Individuen aufwendige soziale Beziehungen mit Artgenossen eingehen. Prosoziales Verhalten, ein Verhalten zum Wohle Anderer, tritt bevorzugt zwischen Individuen auf, die eine starke gegenseitige Bindung aufweisen. Prosozialität beruht auf Empathie-Fähigkeit, die wiederum ein gewisses Verständnis der emotionalen Lage von Artgenossen voraussetzt. Vögel, insbesondere Papageien und Krähen, sind geeignete Modelle, um Zusammenhänge zwischen sozialer Bindung und prosozialem Verhalten zu untersuchen: sie bilden Langzeit-monogame Paare, die das Jahr hindurch miteinander kooperieren. Ziel dieser Doktorarbeit ist es, herauszufinden, wie soziale Bindungen (verwandtschaftlicher, sexueller, oder freundschaftlicher Natur) prosoziales Verhalten und Empathie beeinflussen. Zu diesem Ziel wurden Studien über Futterteilen und Verhaltensreaktionen auf Stress in verschiedenen sozialen Kontexten durchgeführt. Nymphensittiche (Nymphicus hollandicus) reagierten stärker auf Warnrufe ihres Partners als auf die eines anderen Gruppenmitglieds. Ebenso teilten verwandte Sittiche häufiger Futter miteinander als mit anderen Individuen. Verschiedene Papageienarten bevorzugten in einer Entscheidungssituation prosoziale über egoistische Optionen, wobei unklar bleibt, ob sie die Perspektive ihres Partners verstanden. Dohlen (Corvus monedula), die mit einem für sie unheimlichen neuen Objekt konfrontiert wurden, verbrachten mehr Zeit in gegenseitiger Nähe, wenn sie mit Ihrem Partner als mit einem anderen Individuum getestet wurden. Sie verhielten sich aber in Gegenwart ihres Partners nicht mutiger. Die Ergebnisse legen nahe, dass Bindungen zwischen Individuen prosoziales Verhalten und empathische Reaktionen aufeinander beeinflussen.

In a world with rapidly increasing population that competes for the earth’s limited resources, cooperation is crucial. While research showed that empathizing with another individual in need enhances prosociality, it remains unclear whether correctly inferring the other’s inner, mental states on a more cognitive level (i.e., mentalizing) elicits helping behavior as well. We applied a video-based laboratory task probing empathy and a performance measure of mentalizing in adult volunteers (N = 94) and assessed to which extent they were willing to help the narrators in the videos. We replicate findings that an empathy induction leads to more prosocial decisions. Crucially, we also found that correct mentalizing increases the willingness to help. This evidence helps clarify an inconsistent picture of the relation between mentalizing and prosociality.

While the importance of social affect and cognition is indisputable throughout the adult lifespan, findings of how empathy and prosociality develop and interact across adulthood are mixed and real-life data are scarce. Research using ecological momentary assessment recently demonstrated that adults commonly experience empathy in daily life. Furthermore, experiencing empathy was linked to higher prosocial behavior and subjective well-being. However, to date, it is not clear whether there are adult age differences in daily empathy and daily prosociality and whether age moderates the relationship between empathy and prosociality across adulthood. Here we analyzed experience-sampling data collected from participants across the adult lifespan to study age effects on empathy, prosocial behavior, and well-being under real-life circumstances. Linear and quadratic age effects were found for the experience of empathy, with increased empathy across the three younger age groups (18 to 45 years) and a slight decrease in the oldest group (55 years and older). Neither prosocial behavior nor well-being showed significant age-related differences. We discuss these findings with respect to (partially discrepant) results derived from lab-based and traditional survey studies. We conclude that studies linking in-lab experiments with real-life experience-sampling may be a promising venue for future lifespan studies.