Chimpanzees Help Each Other upon Request

Background

The evolution of altruism has been explained mainly from ultimate perspectives. However, it remains to be investigated from a proximate point of view how and in which situations such social propensity is achieved. We investigated chimpanzees'' targeted helping in a tool transfer paradigm, and discuss the similarities and differences in altruism between humans and chimpanzees. Previously it has been suggested that chimpanzees help human experimenters by retrieving an object which the experimenter is trying to reach. In the present study, we investigated the importance of communicative interactions between chimpanzees themselves and the influence of conspecific partner''s request on chimpanzees'' targeted helping.

Methodology/Principal Findings

We presented two tool-use situations (a stick-use situation and a straw-use situation) in two adjacent booths, and supplied non-corresponding tools to paired chimpanzees in the two booths. For example, a chimpanzee in the stick-use situation was supplied with a straw, and the partner in the straw-use situation possessed a stick. Spontaneous tool transfer was observed between paired chimpanzees. The tool transfer events occurred predominantly following recipients'' request. Even without any hope of reciprocation from the partner, the chimpanzees continued to help the partner as long as the partner required help.

Conclusions/Significance

These results provide further evidence for altruistic helping in chimpanzees in the absence of direct personal gain or even immediate reciprocation. Our findings additionally highlight the importance of request as a proximate mechanism motivating prosocial behavior in chimpanzees whether between kin or non-kin individuals and the possible confounding effect of dominance on the symmetry of such interactions. Finally, in contrast to humans, our study suggests that chimpanzees rarely perform acts of voluntary altruism. Voluntary altruism in chimpanzees is not necessarily prompted by simple observation of another''s struggle to attain a goal and therefore an accurate understanding of others'' desires in the absence of communicative signals.     

The development of contingent reciprocity in children

Cooperation between nonrelatives is common in humans. Reciprocal altruism is a plausible evolutionary mechanism for cooperation within unrelated pairs, as selection may favor individuals who selectively cooperate with those who have cooperated with them in the past. Reciprocity is often observed in humans, but there is only limited evidence of reciprocal altruism in other primate species, raising questions about the origins of human reciprocity. Here, we explore how reciprocity develops in a sample of American children ranging from 3 to 7.5 years of age, and also compare children's behavior to that of chimpanzees in prior studies to gain insight into the phylogeny of human reciprocity. Children show a marked tendency to respond contingently to both prosocial and selfish acts, patterns that have not been seen among chimpanzees in prior studies. Our results show that reciprocity increases markedly with age in this population of children, and by about 5.5 years of age children consistently match the previous behavior of their partners.     

Altruism in Forest Chimpanzees: The Case of Adoption

In recent years, extended altruism towards unrelated group members has been proposed to be a unique characteristic of human societies. Support for this proposal seemingly came from experimental studies on captive chimpanzees that showed that individuals were limited in the ways they shared or cooperated with others. This dichotomy between humans and chimpanzees was proposed to indicate an important difference between the two species, and one study concluded that “chimpanzees are indifferent to the welfare of unrelated group members”. In strong contrast with these captive studies, consistent observations of potentially altruistic behaviors in different populations of wild chimpanzees have been reported in such different domains as food sharing, regular use of coalitions, cooperative hunting and border patrolling. This begs the question of what socio-ecological factors favor the evolution of altruism. Here we report 18 cases of adoption, a highly costly behavior, of orphaned youngsters by group members in Taï forest chimpanzees. Half of the adoptions were done by males and remarkably only one of these proved to be the father. Such adoptions by adults can last for years and thus imply extensive care towards the orphans. These observations reveal that, under the appropriate socio-ecologic conditions, chimpanzees do care for the welfare of other unrelated group members and that altruism is more extensive in wild populations than was suggested by captive studies.     

Helping behaviour and regard for others in capuchin monkeys (Cebus apella)

Altruism is an evolutionary puzzle. To date, much debate has focused on whether helping others without regard to oneself is a uniquely human behaviour, with a variety of empirical studies demonstrating a lack of altruistic behaviour in chimpanzees even when the demands of behaving altruistically seem minimal. By contrast, a recent experiment has demonstrated that chimpanzees will help a human experimenter to obtain an out-of-reach object, irrespective of whether or not they are offered a reward for doing so, suggesting that the cognitions underlying altruistic behaviour may be highly sensitive to situational demands. Here, we examine the cognitive demands of other-regarding behaviour by testing the conditions under which primates more distantly related to humans--capuchin monkeys--help an experimenter to obtain an out-of-reach object. Like chimpanzees, capuchin monkeys helped human experimenters even in the absence of a reward, but capuchins systematically failed to take into account the perspective of others when they stood to obtain food for themselves. These results suggest an important role for perspective taking and inhibition in altruistic behaviour and seem to reflect a significant evolutionary development in the roots of altruism, and specifically in other-regarding behaviour, between the divergence of New World monkeys and apes.     

Chimpanzees empathize with group mates and humans,but not with baboons or unfamiliar chimpanzees

Human empathy can extend to strangers and even other species, but it is unknown whether non-humans are similarly broad in their empathic responses. We explored the breadth and flexibility of empathy in chimpanzees, a close relative of humans. We used contagious yawning to measure involuntary empathy and showed chimpanzees videos of familiar humans, unfamiliar humans and gelada baboons (an unfamiliar species). We tested whether each class of stimuli elicited contagion by comparing the effect of yawn and control videos. After including previous data on the response to ingroup and outgroup chimpanzees, we found that familiar and unfamiliar humans elicited contagion equal to that of ingroup chimpanzees. Gelada baboons did not elicit contagion, and the response to them was equal to that of outgroup chimpanzees. However, the chimpanzees watched the outgroup chimpanzee videos more than any other. The combination of high interest and low contagion may stem from hostility towards unfamiliar chimpanzees, which may interfere with an empathic response. Overall, chimpanzees showed flexibility in that they formed an empathic connection with a different species, including unknown members of that species. These results imply that human empathic flexibility is shared with related species.     

Upstream reciprocity in heterogeneous networks

Many mechanisms for the emergence and maintenance of altruistic behavior in social dilemma situations have been proposed. Indirect reciprocity is one such mechanism, where other-regarding actions of a player are eventually rewarded by other players with whom the original player has not interacted. The upstream reciprocity (also called generalized indirect reciprocity) is a type of indirect reciprocity and represents the concept that those helped by somebody will help other unspecified players. In spite of the evidence for the enhancement of helping behavior by upstream reciprocity in rats and humans, theoretical support for this mechanism is not strong. In the present study, we numerically investigate upstream reciprocity in heterogeneous contact networks, in which the players generally have different number of neighbors. We show that heterogeneous networks considerably enhance cooperation in a game of upstream reciprocity. In heterogeneous networks, the most generous strategy, by which a player helps a neighbor on being helped and in addition initiates helping behavior, first occupies hubs in a network and then disseminates to other players. The scenario to achieve enhanced altruism resembles that seen in the case of the Prisoner's Dilemma game in heterogeneous networks.     

Does Sympathy Motivate Prosocial Behaviour in Great Apes?

Prosocial behaviours such as helping, comforting, or sharing are central to human social life. Because they emerge early in ontogeny, it has been proposed that humans are prosocial by nature and that from early on empathy and sympathy motivate such behaviours. The emerging question is whether humans share these abilities to feel with and for someone with our closest relatives, the great apes. Although several studies demonstrated that great apes help others, little is known about their underlying motivations. This study addresses this issue and investigates whether four species of great apes (Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, Pan paniscus) help a conspecific more after observing the conspecific being harmed (a human experimenter steals the conspecific’s food) compared to a condition where no harming occurred. Results showed that in regard to the occurrence of prosocial behaviours, only orangutans, but not the African great apes, help others when help is needed, contrasting prior findings on chimpanzees. However, with the exception of one population of orangutans that helped significantly more after a conspecific was harmed than when no harm occurred, prosocial behaviour in great apes was not motivated by concern for others.     

Chimpanzees help conspecifics obtain food and non-food items

Chimpanzees (Pan troglodytes) sometimes help both humans and conspecifics in experimental situations in which immediate selfish benefits can be ruled out. However, in several experiments, chimpanzees have not provided food to a conspecific even when it would cost them nothing, leading to the hypothesis that prosociality in the food-provisioning context is a derived trait in humans. Here, we show that chimpanzees help conspecifics obtain both food and non-food items--given that the donor cannot get the food herself. Furthermore, we show that the key factor eliciting chimpanzees' targeted helping is the recipients' attempts to either get the food or get the attention of the potential donor. The current findings add to the accumulating body of evidence that humans and chimpanzees share the motivation and skills necessary to help others in situations in which they cannot selfishly benefit. Humans, however, show prosocial motives more readily and in a wider range of contexts.     

Responses to novel foods in captive chimpanzees

Hesitancy to eat novel foods hampers the immediate enlargement of the diet but serves to limit the risk of ingesting toxic foods. Neophobia has been systematically investigated in only a few primate species, in which it appears to be affected by social influences. Surprisingly, little is known about neophobia in chimpanzees. We studied the response of eight adult captive chimpanzees to 16 foods (foods commonly eaten by humans and never tasted before by chimpanzees). Each novel food was presented twice to the chimpanzee by a familiar or an unfamiliar human. Between the two trials the human ate the food face to face with the chimpanzee (demonstration). Results showed that some foods were almost unanimously accepted, whereas others were not. Moreover, there were marked interindividual differences in food acceptance and consumption; chimpanzees ranged from being almost completely neophobic to accepting almost all foods. Familiarity with the human and the human's demonstration did not affect responses to the foods. The humans' predictions concerning the chimpanzees' acceptance of the different foods were rather good; furthermore, in seven cases out of eight the humans' preferences did not correlate with their predictions on the chimpanzees' preferences. The finding that most captive chimpanzees are initially cautious toward novel foods supports the little information there is regarding this subject in wild chimpanzees. However, the lack of influence of the humans' familiarity and demonstration on the response to food by the chimpanzees calls for more naturalistic studies, in which social influences are provided by group members. Since novel stimuli provide sensory stimulation and elicit exploration and social interest, occasional presentation of novel foods could be a promising and cheap device for feeding enrichment. Zoo Biol 21:539–548, 2002. © 2002 Wiley‐Liss, Inc.     

Evidence for a complex demographic history of chimpanzees

To characterize patterns of genomic variation in central chimpanzees(Pan troglodytes troglodytes) and gain insight into their evolution,we sequenced nine unlinked, intergenic regions, representinga total of 19,000 base pairs, in 14 individuals. When theseDNA sequences are compared with homologous sequences previouslycollected in humans and in western chimpanzees (Pan troglodytesverus), nucleotide diversity is higher in central chimpanzeesthan in western chimpanzees or in humans. Consistent with alarger effective population size of central chimpanzees, levelsof linkage disequilibrium are lower than in humans. Patternsof linkage disequilibrium further suggest that homologous geneconversion may be an important contributor to genetic exchangeat short distances, in agreement with a previous study of thesame DNA sequences in humans. In central chimpanzees, but notin western chimpanzees, the allele frequency spectrum is significantlyskewed towards rare alleles, pointing to population size changesor fine-scale population structure. Strikingly, the extent ofgenetic differentiation between western and central chimpanzeesis much stronger than what is seen between human populations.This suggests that careful attention should be paid to geographicsampling in studies of chimpanzee genetic variation.     

What's in it for me? Self-regard precludes altruism and spite in chimpanzees

Sensitivity to fairness may influence whether individuals choose to engage in acts that are mutually beneficial, selfish, altruistic, or spiteful. In a series of three experiments, chimpanzees (Pan troglodytes) could pull a rope to access out-of-reach food while concomitantly pulling another piece of food further away. In the first study, they could make a choice that solely benefited themselves (selfishness), or both themselves and another chimpanzee (mutualism). In the next two experiments, they could choose between providing food solely for another chimpanzee (altruism), or for neither while preventing the other chimpanzee from receiving a benefit (spite). The main result across all studies was that chimpanzees made their choices based solely on personal gain, with no regard for the outcomes of a conspecific. These results raise questions about the origins of human cooperative behaviour.     

The evolutionary history of human and chimpanzee Y-chromosome gene loss

Recent studies have suggested that gene gain and loss may contribute significantly to the divergence between humans and chimpanzees. Initial comparisons of the human and chimpanzee Y-chromosomes indicate that chimpanzees have a disproportionate loss of Y-chromosome genes, which may have implications for the adaptive evolution of sex-specific as well as reproductive traits, especially because one of the genes lost in chimpanzees is critically involved in spermatogenesis in humans. Here we have characterized Y-chromosome sequences in gorilla, bonobo, and several chimpanzee subspecies for 7 chimpanzee gene-disruptive mutations. Our analyses show that 6 of these gene-disruptive mutations predate chimpanzee-bonobo divergence at approximately 1.8 MYA, which indicates significant Y-chromosome change in the chimpanzee lineage relatively early in the evolutionary divergence of humans and chimpanzees.     

Great tits take greater risk toward humans and sparrowhawks in urban habitats than in forests

Urban animals often take more risk toward humans than their non‐urban conspecifics do, but it is unclear how urbanization affects behavior toward non‐human predators. Responses to humans and non‐human predators may covary due to common mechanisms enforcing a phenotypic correlation. However, while increased tolerance toward humans may be advantageous for urban animals, reduced vigilance toward non‐human predators that can pose actual threat may be costly. Therefore, urban animals may benefit from showing specific responses to different threat levels, such as humans versus non‐human predators, or hostile versus non‐hostile humans. To test these alternatives, we compared responses (latencies to return to nest) of urban and forest‐breeding great tits (Parus major) to familiar hostile and unfamiliar humans as well as one of their common predators, the sparrowhawk (Accipiter nisus). We found that urban birds were more risk‐taking toward both humans and sparrowhawk than forest birds. However, responses to sparrowhawk did not correlate with responses to humans either within or across habitats. This suggests that higher risk‐taking of urban compared to forest‐dwelling great tits toward sparrowhawk may be threat‐specific response to lower predation risk rather than a spillover effect of increased tolerance to humans. Furthermore, birds responded similarly to unfamiliar and familiar (potentially dangerous) humans in both habitats, suggesting that great tits may not adjust their risk‐taking to the threat represented by individual humans. These findings indicate that urban birds may flexibly adjust their risk‐taking to certain, but not all, types of threat.     

Interaction sequences between chimpanzees and human visitors at the Zoo

Data were collected on the behavior and physical characteristics of 259 human visitors and 24 chimpanzees at Chester Zoo. The successive responses of humans and chimpanzees to each other's behavior were recorded, the resulting long sequence being referred to as an interaction sequence. There was no particular set of characteristics that distinguished interactors from noninteractors in either humans or chimpanzees, although there was some evidence that chimpanzees were particularly likely to respond to men carrying objects. Chimpanzee responses were random with respect to the previous human behavior, but human responses were significantly associated with the preceding chimpanzee behavior. In particular, chimpanzee sounds were likely to be followed by human sounds, and begging was likely to be followed by the offer of food. Interaction sequences varied in length, but 9% of chimpanzee-initiated sequences went as far as a ninth interaction. Sequences resulted in the chimpanzees being given food in 25% of human-initiated, but only 8% of chimpanzee-initiated sequences. The results are consistent with the interpretation that humans and chimpanzees are motivated to interact with one another and that the chimpanzees do this primarily to obtain food. © 1995 Wiley-Liss, Inc.     

Visual discrimination of primate species based on faces in chimpanzees

Many primate studies have investigated discrimination of individual faces within the same species. However, few studies have looked at discrimination between primate species faces at the categorical level. This study systematically examined the factors important for visual discrimination between primate species faces in chimpanzees, including: colour, orientation, familiarity, and perceptual similarity. Five adult female chimpanzees were tested on their ability to discriminate identical and categorical (non-identical) images of different primate species faces in a series of touchscreen matching-to-sample experiments. Discrimination performance for chimpanzee, gorilla, and orangutan faces was better in colour than in greyscale. An inversion effect was also found, with higher accuracy for upright than inverted faces. Discrimination performance for unfamiliar (baboon and capuchin monkey) and highly familiar (chimpanzee and human) but perceptually different species was equally high. After excluding effects of colour and familiarity, difficulty in discriminating between different species faces can be best explained by their perceptual similarity to each other. Categorical discrimination performance for unfamiliar, perceptually similar faces (gorilla and orangutan) was significantly worse than unfamiliar, perceptually different faces (baboon and capuchin monkey). Moreover, multidimensional scaling analysis of the image similarity data based on local feature matching revealed greater similarity between chimpanzee, gorilla and orangutan faces than between human, baboon and capuchin monkey faces. We conclude our chimpanzees appear to perceive similarity in primate faces in a similar way to humans. Information about perceptual similarity is likely prioritized over the potential influence of previous experience or a conceptual representation of species for categorical discrimination between species faces.     

Altruism among kin vs. nonkin: effects of cost of help and reciprocal exchange

Evolutionary principles suggest that there will be differences in the nature of altruism directed toward kin vs. nonkin. The present study sought to explore these differences. Participants were 295 undergraduate students who each completed a questionnaire about help exchanged with siblings, cousins, acquaintances or friends. For siblings, cousins and acquaintances, greater relatedness was associated with higher levels of helping. Friends were an exception, however, receiving as much or more help than kin. Consistent with an evolutionary analysis, as the cost of helping increased, kin received a larger share of the help given, whereas nonkin received a smaller share. For low-cost help, people helped friends more than siblings; for medium-cost help, they helped siblings and friends equally; and for high-cost help, they expressed a greater willingness to help siblings than friends. As expected, the level of reciprocal exchange was higher among acquaintances than among friends; however, there was also an unexpectedly high level of reciprocal exchange among kin.     

The perception of self-agency in chimpanzees (Pan troglodytes)

The ability to distinguish actions and effects caused by oneself from events occurring in the external environment is a fundamental aspect of human cognition. Underlying such distinctions, self-monitoring processes are often assumed, in which predicted events accompanied by one's own volitional action are compared with actual events observed in the external environment. Although many studies have examined the absence or presence of a certain type of self-recognition (i.e. mirror self-recognition) in non-human animals, the underlying cognitive mechanisms remain unclear. Here, we provide, to our knowledge, the first behavioural evidence that chimpanzees can perform self/other distinction for external events on the basis of self-monitoring processes. Three chimpanzees were presented with two cursors on a computer display. One cursor was manipulated by a chimpanzee using a trackball, while the other displayed motion that had been produced previously by the same chimpanzee. Chimpanzees successfully identified which cursor they were able to control. A follow-up experiment revealed that their performance could not be explained by simple associative responses. A further experiment with one chimpanzee showed that the monitoring process occurred in both temporal and spatial dimensions. These findings indicate that chimpanzees and humans share the fundamental cognitive processes underlying the sense of being an independent agent.     

How chimpanzees look at pictures: a comparative eye-tracking study

Surprisingly little is known about the eye movements of chimpanzees, despite the potential contribution of such knowledge to comparative cognition studies. Here, we present the first examination of eye tracking in chimpanzees. We recorded the eye movements of chimpanzees as they viewed naturalistic pictures containing a full-body image of a chimpanzee, a human or another mammal; results were compared with those from humans. We found a striking similarity in viewing patterns between the two species. Both chimpanzees and humans looked at the animal figures for longer than at the background and at the face region for longer than at other parts of the body. The face region was detected at first sight by both species when they were shown pictures of chimpanzees and of humans. However, the eye movements of chimpanzees also exhibited distinct differences from those of humans; the former shifted the fixation location more quickly and more broadly than the latter. In addition, the average duration of fixation on the face region was shorter in chimpanzees than in humans. Overall, our results clearly demonstrate the eye-movement strategies common to the two primate species and also suggest several notable differences manifested during the observation of pictures of scenes and body forms.     

The ontogeny of human prosociality: behavioral experiments with children aged 3 to 8

Humans regularly engage in prosocial behavior that differs strikingly from that of even our closest living relatives, the chimpanzees (Pan troglodytes). In laboratory settings, chimpanzees are indifferent when given the opportunity to deliver valued rewards to conspecifics, while even very young human children have repeatedly been shown to behave prosocially. Although this broadly suggests that prosocial behavior in chimpanzees differs from that of young human children, the methods used in prior work with children have also differed from the methods used in studies of chimpanzees in potentially crucial ways. Here we test 92 pairs of 3–8-year-old children from urban American (Los Angeles, CA, USA) schools in a face-to-face task that closely parallels tasks used previously with chimpanzees. We found that children were more prosocial than chimpanzees have previously been in similar tasks, and our results suggest that this was driven more by a desire to provide benefits to others than a preference for egalitarian outcomes. We did not find consistent evidence that older children were more prosocial than younger children, implying that younger children behaved more prosocially in the current study than in previous studies in which participants were fully anonymous. These findings strongly suggest that humans are more prosocial than chimpanzees from an early age and that anonymity influences children's prosocial behavior, particularly at the youngest ages.     

Leptin receptor isoform 219.1: an example of protein evolution by LINE-1-mediated human-specific retrotransposition of a coding SVA element

Phylogenetically new insertions of repetitive sequences may contribute to genome evolution by altering the function of preexisting proteins. One example is the SVA sequence, which forms the C-terminal coding exon of the human leptin receptor isoform 219.1. Here, we report that the SVA insertion into the LEPR locus has occurred after divergence of humans and chimpanzees. The SVA element was inserted into a Hal-1/LINE element present in all monkeys and apes tested. Structural features point toward an integration event that was mediated by the L1 protein machinery acting in trans. Thus, our findings add evidence to the hypothesis that retrotransposition events are a driving force in genomic evolution and that the presence or absence of specific retroelements are one distinguishing feature that separates humans from chimpanzees.