Browsing by Author "Hare, Brian A"

Humans universally demonstrate intrinsically motivated prosocial behavior towards kin, non-kin ingroup members, and strangers. However, humans struggle to extend the same prosocial behavior to more abstract concepts like future-others and non-human species. The Adaptive Motivation Hypothesis posits that humans evolved intrinsic motivations to act prosocially towards more tangible social partners like those within an individual’s ingroup, but prosocial behavior towards more distant and abstract partners is constrained by ecological certainty. Prosocial behavior towards these more abstract concepts is more variable and more likely motivated by extrinsic reward. This dissertation aims to examine the development of motivations for prosocial behavior towards these more abstract concepts. My studies rely on common goods games as a proxy for examining behavior towards abstract recipients of prosocial behavior. Common goods are any resource like forests or fisheries that are non-excludable to a population, but rivalrous. In-demand common goods require cooperation of humans to ensure sustainable use in order to avoid depletion. Chapter One examined how children in three populations that differed in ecological certainty behaved in a common goods game where they were asked to contribute portions of their personal endowment to the maintenance of a forest. Participants were either provided a high extrinsic motivation, a low extrinsic motivation, or no extrinsic motivation for contributing to the maintenance of the common good. Results show that overall, children of all ages were more motivated to contribute to abstract recipients when extrinsic motivation is high. However, noticeable variation in behavior between populations was driven by ecological and cultural differences. Chapter Two examined whether aggregated extrinsic rewards increased contributions to common goods in a sample of children aged six to fourteen. Results suggest that both information about personal loss and delay in an acquiring resource together dramatically increase children’s contributions to common goods within both experimental and real-world contexts. Chapter Three explores whether making a typically abstract social partner more tangible increases an individual’s prosocial behavior towards said partner. Results for Chapter Three, conducted with a population in the Democratic Republic of the Congo, find that increasingly the tangibility of an abstract population marginally increases prosocial behavior in children but not in adults. Together, the results of these studies have implications improved understanding of the development of prosocial motivations in school age children, as well as applications to understanding motivations for socially conscious behavior in the face of environmental and conservation dilemmas.

Humans are paradoxical in their ability for extreme kindness and cruelty. The goal of this dissertation is to further uncover the psychological mechanism(s) that allow humans to accept harm directed at members of other groups. The human self-domestication hypothesis proposes that human unique forms of mentalizing evolved as a byproduct of selection for ingroup prosociality. Hare (2017) proposed that late in human evolution Homo sapiens bonded more closely with ingroup members and more skillfully read the mental states of others. Moral and cultural behaviors expanded, and modern human behavior emerged. However, more closely bonded groups tend to perceive outgroup strangers as more threatening. It became advantageous to deny some forms of human-unique mental states to individuals from threatening groups. In this way emotional and moral constraints on violence toward other humans can be escaped. The potential for lethal aggression and harm toward outgroup strangers became even more extreme as a result. According to this model there should be strong psychological links between group identity, mental state attribution, moral exclusion, and a willingness to harm others. Two main mechanisms have been proposed to provide this link. The first is dehumanization or the ability to deny fully human emotions and mental abilities to another person or group of people (Haslam, 2006). The second is social dominance orientation or the perception of a hierarchy between different human groups (Sidanius & Pratto, 2001). Together these mechanisms can override individual characteristics that lead to concern. Group identity alone can be used to indicate inferiority or less than human status. Moral exclusion and harm can follow. More recently a third moderating factor has been proposed. Costello & Hodson (2010) proposed that beliefs about animals strongly shape tendencies to dehumanize. Seeing animals as having human-like minds negates the negative impact of dehumanization since being nonhuman is so similar to being human. In Chapter 1, I combine this evolutionary model with the proposed mechanisms that drive the worst forms of group-based aggression to propose the Dehumanization of Inferior Groups (DIG) Hypothesis. The DIG hypothesis suggests the perception of other groups of humans is strongly modulated by how we view the minds of other animals, their relationship with each other and our relationship to them. Our minds evolved to distinguish between humans and animals, but we develop the ability to categorize some members of our own species as more animal-like. We also evolved to categorize the relative equality or inequality of different groups. This includes groups of animals that can be perceived as different but equal or ranked hierarchically. How we perceive different groups of animals will relate to how hierarchically we view different groups within our own species. The present dissertation seeks to provide initial tests of the DIG hypothesis. To do so, I used experiment-based surveys, investigating behavioral patterns of adults and school age children. In Chapter 2, I assessed dehumanizing tendency in adults and children, revealing that variety of humanness representations can elicit dehumanization in both age groups. Similar to the links seen in previous investigations of adults, children’s willingness to dehumanize is related to their acceptance that other groups can be inferior and more deserving of punishment. In Chapter 3, I examined the association between the perception of animal-to-human similarity and dehumanization. Results in adults and children showed that highlighting mental similarities between animals and humans could narrow down the perceived animal-human divide. However, in both age group, this manipulation does not attenuate dehumanization or the intergroup biases associated with it. Chapter 4 explored the association between the treatment of other human groups and the treatment of animals in a variety of participants who were engaged in different relationship with animals. I found that people who endorsed discrimination of dog breeds also endorsed group-based discrimination in human society. Moreover, positive contact with dogs is associated with disapproval of group-based inequality. Together, these findings suggest that the perception of human intergroup relations and the perception of relationship among animal groups are dependent upon similar cognitive processes. The studies presented here have implications for understanding psychological origins of dehumanization as well as designing interventions to promote intergroup tolerance.

Humans are natural politicians. We obsessively collect social information that is both observable (e.g., about third-party relationships) and unobservable (e.g., about others’ psychological states), and we strategically employ that information to manage our cooperative and competitive relationships. To what extent are these abilities unique to our species, and how did they evolve? The present dissertation seeks to contribute to these two questions. To do so, I take a comparative perspective, investigating social decision-making in humans’ closest living relatives, bonobos and chimpanzees. In Chapter 1, I review existing literature on theory of mind—or the ability to understand others’ psychological states—in these species. I also present a theoretical framework to guide further investigation of social cognition in bonobos and chimpanzees based on hypotheses about the proximate and ultimate origins of their species differences. In Chapter 2, I experimentally investigate differences in the prosocial behavior of bonobos and chimpanzees, revealing species-specific prosocial motivations that appear to be less flexible than those exhibited by humans. In Chapter 3, I explore through decision-making experiments bonobos’ ability to evaluate others based on their prosocial or antisocial behavior during third-party interactions. Bonobos do track the interactions of third-parties and evaluate actors based on these interactions. However, they do not exhibit the human preference for those who are prosocial towards others, instead consistently favoring an antisocial individual. The motivation to prefer those who demonstrate a prosocial disposition may be a unique feature of human psychology that contributes to our ultra-cooperative nature. In Chapter 4, I investigate the adaptive value of social cognition in wild primates. I show that the recruitment behavior of wild chimpanzees at Gombe National Park, Tanzania is consistent with the use of third-party knowledge, and that those who appear to use third-party knowledge receive immediate proximate benefits. They escape further aggression from their opponents. These findings directly support the social intelligence hypothesis that social cognition has evolved in response to the demands of competing with one’s own group-mates. Thus, the studies presented here help to better characterize the features of social decision-making that are unique to humans, and how these abilities evolved.

Homo sapiens’ capacity for cooperative communication enables us adapt to new environments more rapidly than any other species via the process of cumulative cultural evolution, but the evolutionary processes which led to this capacity remain an open question (Boyd & Richerson, 1995; Henrich & McElreath, 2003; Hill et al., 2009; Mesoudi & Thornton, 2018; Tomasello, 1999). One proposed explanation for this capacity is the human self-domestication hypothesis (SDH), which posits that cooperative communication was altered via shifts in development as a by-product of self-selecting against aggression and for prosociality (Hare, 2017; Hare et al., 2012). Dogs have been hypothesized to have undergone the same process during their domestication, resulting in human-like cooperative communicative abilities (Hare, 2017). If so, this convergence could make dogs a critical model for human self-domestication. The present dissertation evaluates this hypothesis by testing three resulting predictions: 1) that dogs’ understanding of communicative intentions is actually “human-like” (i.e. spontaneous and flexible), which we tested through a series of gesture reading tasks with adult dogs; 2) that these qualities are a result of domestication, and therefore expressed more strongly and at an earlier age in dogs compared to wolves, which we tested by running dog and wolf puppies through a cross-sectional battery of cognitive and temperament tasks; and 3) that dogs show early emerging and expanded windows of social development relative to other non-social cognitive abilities, indicating a similar developmental pattern as is observed in humans, which we tested by running puppies through a longitudinal battery containing nine cognitive tasks during the period of rapid brain development. Strong support was found for predictions 1 and 2, and some support was found for prediction 3, with more work being needed to draw stronger conclusions. We conclude that dogs’ cooperative communicative abilities are convergent with those of humans at the levels of behavior, cognition, and potentially development as well.

Humans are champions of prosociality. Across different cultures and early in life, humans routinely engage in prosocial behaviors that benefit others. Perhaps most strikingly, humans are even prosocial toward strangers (i.e. xenophilic). This is an evolutionary puzzle because it cannot be explained by kinship theory, reciprocal altruism or reputation. The parochialism hypothesis proposes that this extreme prosociality is unique to humans, is motivated by unselfish motivation and evolved through group selection made possible by human culture and warfare. The first impression hypothesis, on the other hand, proposes that xenophilia can evolve to promote the selfish benefits that accrue from extending one's social network. It predicts that 1) nonhuman species can evolve prosociality toward strangers when the benefit of forming new relations is higher than the cost, 2) the motivation for prosociality can be selfish, and 3) encounters with strangers can be a positive social event since strangers represent potential social partners. This dissertation presents three sets of experiments designed to test these predictions with bonobos (Pan paniscus), a species known for reduced xenophobia. These experiments showed, first, that bonobos voluntarily shared monopolizable food with a stranger and helped the stranger to obtain out-of-reach food. Second, the observed prosociality was driven by a selfish motivation to initiate an interaction with the stranger in close proximity and an other-regarding motivation to benefit the stranger. Third, an involuntary yawning task and a voluntary choice task show converging results that bonobos attribute positive valence to completely unknown strangers by default. These experiments support the three core predictions of the first impression hypothesis and challenge the view that intergroup competition is crucial to the origin of prosociality toward strangers in our species. Instead, the first impression hypothesis proposes that xenophilia in bonobos is probably an adaptation to initiating non-kin cooperation. Because female bonobos are highly cooperative even though they are the dispersing sex, xenophilia might function to quickly establish cooperative relationships with new immigrants. This suggests that xenophilia and reciprocity are likely two complementary aspects of non-kin cooperation: the former explains its initiation while the latter explains its maintenance. Similarly, xenophilia in humans is likely a result of the increasing need for cooperation among non-kin due to enhanced fission-fusion dynamics, population expansion, obligate cooperative foraging and greater dependence on cultural knowledge.

Primates in the wild face complex foraging decisions where they must assess the most valuable of different potential resources to exploit, as well recall the location of options that can be widely distributed. While differences in diet and ecology have long been thought to be an important factor influencing brain evolution in primates, it is less well understood what psychological abilities animals actually use when making foraging decisions. This dissertation examines cognitive domains that play a crucial role in supporting foraging behaviors--spatial memory and decision-making--by integrating both psychological and biological approaches to behavior. In particular, the research presented here examines multiple species of primates to address the cognitive skills that different animals use to solve foraging problems (at the proximate level of analysis), as well as why some species appear to solve such problems differently than other species (at the ultimate level of analysis).

The first goal of the dissertation is to compare closely-related species that vary in ecological characteristics, in order to illuminate how evolution shapes the cognitive skills used in foraging contexts. This component focuses on comparisons between chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), humans' closest extant relatives. In addition, this component reports comparisons amongst strepsirrhines (Lemur catta, Eulemur mongoz, Propithecus coquereli, and Varecia subsp.) to model cognitive evolution in a taxonomic group with greater ecological diversity than Pan. The first two chapters test the hypothesis that more frugivorous species exhibit more accurate spatial memory skills, first by comparing apes' spatial memory abilities (Chapter 2), and then by comparing four species of lemurs on a related set of spatial memory tasks (Chapter 3). In subsequent chapters, I examine apes' decision-making strategies to test the hypothesis that chimpanzees are more willing to pay decision-making costs than are bonobos, due to differences in their feeding ecology. I focus on preferences about the timing of payoffs (Chapter 4); preferences about risk, or the variability in payoffs (Chapters 4 and 5); and preferences about ambiguity, or knowledge about available options (Chapter 6).

The second goal of the dissertation is to compare the psychological mechanisms that human and nonhuman great apes use for foraging, in order to identify potentially human-unique cognitive abilities. In terms of spatial memory, I examine whether other apes also exhibit human-like patterns of spatial memory development (Chapter 2). In terms of decision-making, I examine whether apes exhibit a suite of human-like biases when making value-based choices. In particular, I test whether emotional and motivational processes, which are critical components of human decision-making, also play a role in apes' choices (Chapters 4); whether apes are sensitive to social context when making economic decisions (Chapter 5); and whether apes are sensitive to their degree of knowledge when making choices under uncertainty (Chapter 6). Finally, I directly compare human and ape preferences on a matched task to assess whether humans use any unique psychological abilities when making decisions about risk (Chapter 7). In sum, this dissertation links studies of mechanism with hypotheses about function in order to illuminate the evolutionary roots of human's unique cognitive phenotype.

What makes our minds human? How did they evolve to be this way? This dissertation presents data from two complementary lines of research driven by these orienting questions. The first of these explores the `what' of human cognitive evolution through comparative studies with chimpanzees and bonobos. The general aim of these studies is to understand which aspects of cognition are unique to humans, and which are shared with our closest living relatives. Chapters 2-3 test the hypothesis that humans have unique cognitive skills for reasoning about the attention of other individuals (theory of mind), and unique motivation to use these skills in cooperative contexts with conspecifics. In Chapter 2 I show that understanding others' attention is unlikely to be the `small difference that makes the big difference', as some researchers have proposed. However, my data support the possibility that species differences in the ontogeny of these skills may have robust consequences for the adult cognitive phenotype. In Chapter 3 I show that (contrary to previous reports) nonhuman apes are also motivated to engage in some simple triadic social activities, which resemble those characteristic of human children. Again however, I identify important differences between humans and other apes in their spontaneous preferences for these types of activities, and their attitudes toward a partner when cooperative behaviors are interrupted. The second half of this dissertation (Chapters 4-5) explores the `why' and `how' of cognitive evolution. Chapter 4 outlines the kind of research questions and methods that comparative psychologists will need to embrace in order to use the comparative method to its full potential in the study of cognitive evolution. Chapter 5 provides a proof of principle for this approach using a dataset including 33 species tested on two cognitive tasks measuring inhibitory control. Here I show that cognitive skills for inhibitory control are closely related to phylogeny across species, and strongly predicted by absolute (but not relative) brain size. Further, I show that two of the other leading hypotheses put forth to explain primate intelligence, namely sociality and diet, do not predict cognitive skills on these tasks. These data illustrate the power of the comparative method for understanding cognitive evolution, and provide a starting point for future studies embracing this approach. Collectively, this research refines our understanding of how human cognition differs from that of other primates, and illustrates the utility of studying cognitive evolution from an explicitly phylogenetic comparative framework.