2018 and in press
Rosati, A.G., DiNicola, L., & Buckholtz, J.W. (in press). Chimpanzee cooperation is fast, and independent from self-control. Psychological Science. Abstract
Large-scale cooperation is a hallmark of our species that appears unique amongst primates. Yet the evolutionary mechanisms that drove the emergence of human-like patterns of cooperation remain unclear. Studying the cognitive processes underlying cooperative behavior in apes, our closest living relatives, can help identify these mechanisms. Accordingly, we employed a novel test battery to assess the willingness of forty chimpanzees to donate resources, instrumentally help others, and punish a culpable thief. We found that chimpanzees were faster to make prosocial than selfish choices, and that more prosocial individuals made the fastest responses. Further, two measures of self-control did not predict variation in prosocial responding, and individual performance across cooperative tasks did not covary. These results show that chimpanzees and humans share key cognitive processes for cooperation, despite differences in the scope of their cooperative behaviors.
Rosati, A.G., Arre, A.M., Platt, M.L., & Santos, L.R. (2018). Developmental shifts in social cognition: socioemotional biases across the lifespan in rhesus monkeys. Behavioral Ecology and Sociobiology, 72: 63 [PDF] [Video] [Supplementary] [Publisher’s Version] Abstract
Humans exhibit a suite of developmental changes in social cognition across the lifespan. To what extent are these developmental patterns unique? We first review several social domains in which humans undergo critical ontogenetic changes in socio-cognitive processing, including social attention and theory of mind. We then examine whether one human developmental transition—a shift in socioemotional preferences—also occurs in nonhuman primates. Specifically, we experimentally measured socioemotional processing in a large population of rhesus macaques (Macaca mulatta) ranging from infancy to old age. We tested whether macaques, like humans, also exhibited developmental shifts from a negativity bias at younger ages, indicating preferential attention to negative socioemotional stimuli, to a positivity bias at older ages. We first assessed monkeys’ (n = 337) responses to negative socioemotional stimuli by comparing their duration of looking towards photos of negative conspecific signals (threat displays) versus matched neutral expressions. In contrast to the pattern observed in humans, we found that older monkeys were more attentive to negative emotional stimuli than were younger monkeys. In a second study, we used the same method to examine monkeys’ (n = 132) attention to positive (affiliative displays) versus matched neutral expressions. Monkeys did not exhibit an overall preference for positive stimuli, nor major age-related changes in their attention. These results indicate that while monkeys show robust ontogenetic shifts in social preferences, they differ from humans by exhibiting an increasing negativity bias with age. Studies of comparative cognitive development can therefore provide insight into the evolutionary origins of human socio-cognitive development.
Stokes, R., Tully, G., & Rosati, A. G. (2018). Pan African Sanctuary Alliance: securing a future for the African great apes. International Zoo Yearbook, 52, 1-9. [PDF] [Publisher’s Version] Abstract
The Pan African Sanctuary Alliance (PASA) is the unified voice of primate rescue and rehabilitation projects in Africa, and includes 23 member organizations in 13 countries. PASA improves animal welfare by regularly evaluating these sanctuaries to ensure that they operate at a high standard of care, building the capacity of sanctuary staff and providing crisis support to mitigate emergencies. Moreover, PASA works with its member organizations to raise awareness globally about wildlife issues and to conduct other large-scale conservation projects. In these endeavours, PASA benefits greatly from the local experience and connections of its member organizations. Finally, nearly all PASA- member sanctuaries host researchers, thereby contributing to our knowledge of the great apes and other African primates. Much of PASA’s work is made possible by support from zoos around the world. A brief precis of the current work carried out by PASA and its member organizations is given, along with descriptions of conservation programmes that are planned for the future.
Rosati, A. G. (2017). Foraging cognition: Reviving the ecological intelligence hypothesis. Trends in Cognitive Sciences, 21, 691-702. [PDF] [Publisher’s Version] Abstract
What are the origins of intelligent behavior? The demands associated with living in complex social groups have been the favored explanation for the evolution of primate cognition in general and human cognition in particular. However, recent comparative research indicates that ecological variation can also shape cognitive abilities. I synthesize the emerging evidence that ‘foraging cognition’ – skills used to exploit food resources, including spatial memory, decision-making, and inhibitory control – varies adaptively across primates. These findings provide a new framework for the evolution of human cognition, given our species’ dependence on costly, high-value food resources. Understanding the origins of the human mind will require an integrative theory accounting for how humans are unique in both our sociality and our ecology.
Rosati, A. G., & Santos, L. R. (2017). Tolerant Barbary macaques maintain juvenile levels of social attention in old age, but despotic rhesus macaques do not. Animal Behaviour, 130, 199-207 [PDF] [Supplementary] [Publisher’s Version] Abstract
Complex social life is thought to be a major driver of complex cognition in primates, but few studies have directly tested the relationship between a given primate species’ social system and their social cognitive skills. We experimentally compared life span patterns of a foundational social cognitive skill (following another’s gaze) in tolerant Barbary macaques, Macaca sylvanus, and despotic rhesus macaques, Macaca mulatta. Semi-free-ranging monkeys (N = 80 individuals from each species) followed gaze more in test trials where an actor looked up compared to control trials. However, species differed in ontogenetic trajectories: both exhibited high rates of gaze following as juveniles, but rhesus monkeys exhibited declines in social attention with age, whereas Barbary macaques did not. This pattern indicates that developmental patterns of social attention vary with social tolerance, and that diversity in social behaviour can lead to differences in social cognition across primates.
Stokes, R., Tully, G., & Rosati, A. (2017). Pan African Sanctuary Alliance: Primate welfare, conservation, and research. African Primates, 12: 59-64. [PDF] [Publisher’s Version] Abstract
The Pan African Sanctuary Alliance (PASA), the largest association of wildlife centers in Africa, includes 22 organizations that collectively house more than 3,000 rescued primates. Prior to PASA’s formation, these organizations had similar goals and were facing similar challenges, but typically did not communicate with one another. In 2000, conservationists and primatologists arranged a meeting in Uganda to bring these groups together for the first time. The directors of the organizations agreed there was a need for improved ongoing communication and, as a result, PASA was formed. Although PASA’s headquarters is now in Portland, Oregon and it is a registered nonprofit in the United States, it was created by the African wildlife centers. Despite working in extraordinarily challenging conditions, members of the Alliance are making significant strides in primate welfare and conservation. They collaborate with law enforcement agencies to reduce wildlife crime by rescuing confiscated animals, give lifelong care to primates orphaned by the bushmeat trade and the illicit pet trade, work to stop the hunting and tracking of endangered species, defend critical habitat from exploitation, and conduct community development and education programs reaching more than 500,000 people each year across Africa. Additionally, PASA member wildlife centers provide employment for nearly 700 Africans and inject millions of dollars into local economies.
Rosati, A.G. (2017). Chimpanzee cognition and the roots of the human mind. In: Chimpanzees and Human Evolution (M. Muller, R. Wrangham & D. Pilbeam, eds.). Cambridge: The Belknap Press of Harvard University Press, pp. 703-745. [PDF] Abstract
The origins of the human mind have been a puzzle ever since Darwin (1871, 1872). Despite striking continuities in the behavior of humans and nonhumans, our species also exhibits a suite of abilities that diverge from the rest of the animal kingdom: we create and utilize complex technology, pass cultural knowledge from generation to generation, and cooperate across numerous and diverse contexts. Why do humans exhibit these abilities, but other animals (mostly) do not? This is a fundamental question in biology, psychology, and philosophy. This puzzle involves two main parts. The first is concerned with identifying the psychological capacities that are unique to humans. This phylogenetic question can be addressed through careful comparisons of humans and other animals to pinpoint the cognitive traits that are likely derived in our species. The second is concerned with the function of these capacities, and the context in which they arose. This evolutionary question examines why, from an ultimate perspective, we evolved these specialized capacities in the first place. Solving these puzzles poses a special challenge because it is only possible to directly measure the cognition of living animals. The bodies of extinct species leave traces in the fossil record, and even some behavioral traits exhibit well-understood relationships with physical traits—such as relationships between dentition and dietary ecology, or mating system and sexual size dimorphism. These relationships provide important benchmarks when biologists infer the behavior of extinct species. Unfortunately, cognition does not fossilize, and neither do the brains that generate cognitive abilities. Even those features of neuroanatomy that do leave some trace in the fossil record—such as brain size or particular anatomical landmarks—are often related to the kinds of complex cognitive capacities potentially unique to humans in a coarse fashion. As such, identifying derived human cognitive traits requires reconstructing the mind of the last common ancestor of chimpanzees (Pan troglodytes), bonobos (Pan paniscus), and humans (Homo sapiens). This reconstruction then can be used to infer what cognitive characteristics have changed in the human lineage.
Rosati, A.G. (2017). Ecological variation in cognition: Insights from bonobos and chimpanzees. In: Bonobos: Unique in Mind, Brain and Behavior (B. Hare & S. Yamamoto, eds.). Oxford: Oxford University Press, pp. 157-170. [PDF] Abstract
Bonobos and chimpanzees are closely related, yet they exhibit important differences in their wild socio-ecology. Whereas bonobos live in environments with less seasonal variation and more access to fallback foods, chimpanzees face more competition over spatially distributed, variable resources. This chapter argues that bonobo and chimpanzee cognition show psychological signatures of their divergent wild ecology. Current evidence shows that despite strong commonalities in many cognitive domains, apes express targeted differences in specific cognitive skills critical for wild foraging behaviours. In particular, bonobos exhibit less accurate spatial memory, reduced levels of patience and greater risk aversion than do chimpanzees. These results have implications for understanding the evolution of human cognition, as studies of apes are a critical tool for modelling the last common ancestor of humans with nonhuman apes. Linking comparative cognition to species’ natural foraging behaviour can begin to address the ultimate reason for why differences in cognition emerge across species.
Rosati, A. G. (2017). Decisions under uncertainty: preferences, biases, and choice. In: APA Handbook of Comparative Psychology, Vol. 2 (J. Call, ed.). The American Psychological Association, pp. 329-357. [PDF] Abstract
Imagine a choice between two potential jobs: a position that is stable but intellectually mundane, or one that is more exciting but offers only short contract with some chance of renewal. These kinds of decisions can be agonizing because they involve uncertainty. While the first job option is a known quantity, the second job offers the possibility of being more fulfilling, but also the possibility of being let go in the near future. This uncertainty means that it is not possible to know the exact consequences of the decision in advance, making it difficult to judge the best course of action. Many important decisions involve this same sort of uncertainty—such as whether to invest in a new business, commit to a partner, or pursue a medical treatment. Yet uncertainty is not something only humans experience: it is pervasive in the natural world, and all animals must sometimes make decisions without complete information about the consequences of their actions. Consequently, illuminating how decision-makers respond to uncertainty is a problem of interest across both the social and biological sciences. This review will integrate theory from economics, psychology, and biology in order to understand the psychological mechanisms that animals use to make decisions under uncertainty, as well as what biological function these mechanisms might have. I further argue that comparative research is a powerful tool for understanding the nature of economic decision-making. Discovering that a particular decision-making pattern is widely shared across humans and other species—or conversely, unique to humans alone—can provide important insights about the types of experiences that engender these psychological processes.
Rosati, A. G. (2017). The evolution of primate executive function: from response control to strategic decision-making. In: Evolution of Nervous Systems, 2nd ed., Vol. 3 (J. Kaas & L. Krubitzer, eds.). Amsterdam: Elsevier, pp. 423–437. [PDF] Abstract
Human cognition is permeated by self-control: the ability to engage in complex, goal-oriented behaviors rather than just react to the moment at hand. This chapter examines the evolutionary roots of these abilities by comparing the psychological capacities of humans and other primates. In fact, there is marked variation in how different primate species control their motoric responses to inhibit prepotent but ineffectual actions, engage in strategic decision-making to determine the best course of action, and learn and update their responses when contingencies change. Understanding how and why this variation emerged can shed light on the origins of human cognition.
Rosati, A. G., & Santos, L. R. (2016). Spontaneous metacognition in rhesus monkeys. Psychological Science , 27, 1181 –1191. [PDF] [Videos] [Publisher’s Version] Abstract
Metacognition is the ability to think about thinking. Although monitoring and controlling one’s knowledge is a key feature of human cognition, its evolutionary origins are debated. In the current study, we examined whether rhesus monkeys (Macaca mulatta; N = 120) could make metacognitive inferences in a one-shot decision. Each monkey experienced one of four conditions, observing a human appearing to hide a food reward in an apparatus consisting of either one or two tubes. The monkeys tended to search the correct location when they observed this baiting event, but engaged in information seeking—by peering into a center location where they could check both potential hiding spots—if their view had been occluded and information seeking was possible. The monkeys only occasionally approached the center when information seeking was not possible. These results show that monkeys spontaneously use information about their own knowledge states to solve naturalistic foraging problems, and thus provide the first evidence that nonhumans exhibit information-seeking responses in situations with which they have no prior experience.
Rosati, A. G., & Hare, B. (2016). Reward type modulates human risk preferences. Evolution and Human Behavior, 37, 159–168. [PDF] [Supplementary] [Publisher’s Version] Abstract
Money and biological rewards differ in many ways. Yet studies of human decision-making typically involve money, whereas nonhuman studies involve food. We therefore examined how context shifts human risk preferences to illuminate the evolution of decision-making. First, we assessed peoples’ risk preferences across food, prizes, and money in a task where individuals received real rewards and learned about payoffs through experience. We found that people were relatively more risk-seeking for both food and prizes compared to money—indicating that people may treat abstract reward markers differently from concrete rewards. Second, we compared human risk preferences for food with the performance of our closest phylogenetic relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), in order to illuminate the evolutionary origins of human decision-making strategies. In fact, human and chimpanzees were both relatively more risk-seeking compared to bonobos. Finally, we investigated why people respond differently to money versus concrete rewards when making decisions. We found that people were more risk-prone when making decisions about money that was constrained as a store of value, compared to money that could be freely exchanged. This shows that people are sensitive to money’s usefulness as a store of value that can be used to acquire other types of rewards. Our results indicate that humans exhibit different preferences when making risky decisions about money versus food, an important consideration for comparative research. Furthermore, different psychological processes may underpin decisions about abstract rewards compared to concrete rewards.
Rosati, A. G., Arre, A. M., Platt, M. L., & Santos, L. R. (2016). Rhesus monkeys show human-like changes in gaze following across the lifespan. Proceedings of the Royal Society B , 283, 20160376. [PDF] [Supplementary Material] [Study Videos] [Publisher’s Version] Abstract
Gaze following, or co-orienting with others, is a foundational skill for human social behaviour. The emergence of this capacity scaffolds critical human-specific abilities such as theory of mind and language. Non-human primates also follow others’ gaze, but less is known about how the cognitive mechanisms supporting this behaviour develop over the lifespan. Here we experimentally tested gaze following in 481 semi-free-ranging rhesus macaques (Macaca mulatta) ranging from infancy to old age. We found that monkeys began to follow gaze in infancy and this response peaked in the juvenile period—suggesting that younger monkeys were especially attuned to gaze information, like humans. After sexual maturity, monkeys exhibited human-like sex differences in gaze following, with adult females showing more gaze following than males. Finally, older monkeys showed reduced propensity to follow gaze, just as older humans do. In a second study (n = 80), we confirmed that macaques exhibit similar baseline rates of looking upwards in a control condition, regardless of age. Our findings indicate that—despite important differences in human and non-human primate life-history characteristics and typical social experiences—monkeys undergo robust ontogenetic shifts in gaze following across early development, adulthood and ageing that are strikingly similar to those of humans.
Bettle, R., & Rosati, A. G. (2016). Understanding human gaze. In: Encyclopedia of Evolutionary Psychological Science (T. Shackelford and V. Weekes-Shackelford, eds.) Springer, pp. 1-4. [PDF] [Publisher’s Version] Abstract
Social attention is a foundational component of human social behavior. Our ability to detect and think about the direction of other’s gaze involves the attribution of mental states to others and scaffolds the development of other complex cognitive skills. Gaze-following is also widespread among other primates, but the cognitive mechanisms underlying gaze-sensitive behaviors appear to differ across species. Understanding the evolutionary origins of human social attention capacities can reveal the roots of our species’ unique patterns of cognition and culture.
Rosati, A. G. (2016). Uncovering the behavior and cognition of the earliest stone tool makers. Evolutionary Anthropology , 25, 269–270. [Publisher’s Version] [PDF] Abstract
In August 2016, the 13th Human Evolution Workshop at the Turkana Basin Institute (TBI) brought together a diverse group of scientists from archeology, paleontology, geology, primatology, cognition, and neuroscience. Organized by Sonia Harmand (Stony Brook and TBI), and Helene Roche (Centre National de la Recherche Scientifique) along with TBI director Lawrence Martin (Stony Brook), the workshop focused on the earliest evidence of stone knapping. This focus was spurred by the recent discovery of stone tools at the Lomekwi 3 site in Kenya, which have been dated to 3.3 Mya. It is suspected that these tools were produced by Kenyathropus platyops, the only hominin found in the region during that period. As delineated by Richard Leakey (Stony Brook and TBI), our task was to assess whether these tools represent a “cognitive Rubicon” —a fundamental transition in our lineage that demarcates the human species.
Rosati, A. G., & Warneken, F. (2016). How comparative cognition can shed light on human evolution: Response to Beran et al.’s discussion of “Cognitive capacities for cooking in chimpanzees”. Learning & Behavior, 44, 109-115. [PDF] [Publisher’s Version] Abstract
We recently reported a study (Warneken & Rosati, 2015) examining whether chimpanzees possess several cognitive capacities that are critical to engage in cooking. In a subsequent commentary, Beran, Hopper, de Waal, Sayers, and Brosnan (2015) asserted that our paper has several flaws. Their commentary (1) critiques some aspects of our methodology and argues that our work does not constitute evidence that chimpanzees can actually cook; (2) claims that these results are old news, as previous work had already demonstrated that chimpanzees possess most or all of these capacities; and, finally, (3) argues that comparative psychological studies of chimpanzees cannot adequately address questions about human evolution, anyway. However, their critique of the premise of our study simply reiterates several points we made in the original paper. To quote ourselves: “As chimpanzees neither control fire nor cook food in their natural behavior, these experiments therefore focus not on whether chimpanzees can actually cook food, but rather whether they can apply their cognitive skills to novel problems that emulate cooking” (Warneken & Rosati, 2015, p. 2). Furthermore, the methodological issues they raise are standard points about psychological research with animals—many of which were addressed synthetically across our 9 experiments, or else are orthogonal to our claims. Finally, we argue that comparative studies of extant apes (and other nonhuman species) are a powerful and indispensable method for understanding human cognitive evolution.
Leimgruber, K. L., Rosati, A. G., & Santos, L. R. (2016). Capuchins punish those who have more. Evolution and Human Behavior, 37, 236–244. [PDF] [Supplementary] [Publisher’s Version] Abstract
Punishment of non-cooperators is important for the maintenance of large-scale cooperation in humans, but relatively little is known about the relationship between punishment and cooperation across phylogeny. The current study examined second-party punishment behavior in a nonhuman primate species known for its cooperative tendencies—the brown capuchin monkey (Cebus apella). We found that capuchins consistently punished a conspecific partner who gained possession of a food resource, regardless of whether the unequal distribution of this resource was intentional on the part of the partner. A non-social comparison confirmed that punishment behavior was not due to frustration, nor did punishment stem from increased emotional arousal. Instead, punishment behavior in capuchins appears to be decidedly social in nature, as monkeys only pursued punitive actions when such actions directly decreased the welfare of a recently endowed conspecific. This pattern of results is consistent with two features central to human cooperation: spite and inequity aversion, suggesting that the evolutionary origins of some human-like punitive tendencies may extend even deeper than previously thought.
Krupenye, C., Rosati, A. G., & Hare, B. (2016). What’s in a frame? Response to comments on “Bonobos and chimpanzees exhibit human-like framing effects”. Biology Letters, 12, 20150959. [PDF] [Publisher’s Version] Abstract
We recently reported a study where chimpanzees and bonobos faced decisions between a ‘framed’ option that provided either one or two pieces of fruit, and an alternative option that always provided a constant number of peanuts. We found that apes (especially males) chose the framed option more when it was presented as a gain—apes initially saw one piece of fruit, but sometimes got two after making a choice—than when it was framed as a loss—apes saw two fruits, but sometimes received only one. We argued that the apes showed human-like framing effects, because they judged the fruit option as more desirable when it was presented as a gain than as a loss, despite equivalent payoffs. In a commentary, Kanngiesser & Woike claimed that the apes actually exhibited a pattern opposite of that typically seen in humans. They further highlighted important differences between human and non- human animal decision-making tasks. We believe that the commentary missed a critical aspect of our methodology, as they interpreted our results in terms of risky choice framing—or the reflection effect—whereas our task was designed to probe attribute framing.
Warneken, F., & Rosati, A. G. (2015). Cognitive capacities for cooking in chimpanzees. Proceedings of the Royal Society B, 282, 20150229. [PDF] [Supplementary] [Videos] [Publisher’s Version] Abstract
The transition to a cooked diet represents an important shift in human ecology and evolution. Cooking requires a set of sophisticated cognitive abilities, including causal reasoning, self-control and anticipatory planning. Do humans uniquely possess the cognitive capacities needed to cook food? We address whether one of humans’ closest relatives, chimpanzees (Pan troglodytes), possess the domain-general cognitive skills needed to cook. Across nine studies, we show that chimpanzees: (i) prefer cooked foods; (ii) comprehend the transformation of raw food that occurs when cooking, and generalize this causal understanding to new contexts; (iii) will pay temporal costs to acquire cooked foods; (iv) are willing to actively give up possession of raw foods in order to transform them; and (v) can transport raw food as well as save their raw food in anticipation of future opportunities to cook. Together, our results indicate that several of the fundamental psychological abilities necessary to engage in cooking may have been shared with the last common ancestor of apes and humans, predating the control of fire.
Krupenye, C., Rosati, A. G., & Hare, B. (2015). Bonobos and chimpanzees exhibit human-like framing effects. Biology Letters, 11, 20140527. [PDF] [Supplementary] [Publisher’s Version] Abstract
Humans exhibit framing effects when making choices, appraising decisions involving losses differently from those involving gains. To directly test for the evolutionary origin of this bias, we examined decision-making in humans’ closest living relatives: bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). We presented the largest sample of non-humans to date (n = 40) with a simple task requiring minimal experience. Apes made choices between a ‘framed’ option that provided preferred food, and an alternative option that provided a constant amount of intermediately preferred food. In the gain condition, apes experienced a positive ‘gain’ event in which the framed option was initially presented as one piece of food but sometimes was augmented to two. In the loss condition, apes experienced a negative ‘loss’ event in which they initially saw two pieces but sometimes received only one. Both conditions provided equal pay-offs, but apes chose the framed option more often in the positive ‘gain’ frame. Moreover, male apes were more susceptible to framing than were females. These results suggest that some human economic biases are shared through common descent with other apes and highlight the importance of comparative work in understanding the origins of individual differences in human choice.
Rosati, A. G. (2015). Context influences spatial frames of reference in bonobos (Pan paniscus). Behaviour, 152, 375-406. [PDF] [Publisher’s Version] Abstract
Primates must solve complex spatial problems when foraging, such as finding patchy resources and navigating between different locations. However, the nature of the cognitive representations supporting these types of behaviors is currently unclear. In humans, there has been great debate concerning the relative importance of egocentric representations (which are viewer-dependent) versus allocentric representations (which are based on aspects of the external environment). Comparative studies of nonhuman apes can illuminate which aspects of human spatial cognition are shared with other primates, versus which aspects are unique to our lineage. The current studies therefore examined spatial cognitive development in one of our closest living relatives, bonobos (Pan paniscus) across contexts. The first study assessed how younger bonobos encode locations in a place-response task in which apes first learn that one of two locations is consistently baited with a reward, and then must approach the two locations from a flipped perspective. The second study examined how a larger age sample of bonobos responded to a spatial relations task in which they first experience that one location is baited, and then can generalize this learning to a new set of targets. Results indicated that while bonobos exhibited a predominantly allocentric strategy in the first study, they consistently exhibited an egocentric strategy in the second. Together, these results show that bonobos can use both strategies to encode spatial information, and illuminate the complementary contributions to cognition made by egocentric and allocentric representations.
Santos, L. R., & Rosati, A. G. (2015). The evolutionary roots of human decision-making. Annual Review of Psychology, 66, 321-347. [PDF] [Publisher’s Version] Abstract
Humans exhibit a suite of biases when making economic decisions. We review recent research on the origins of human decision making by examining whether similar choice biases are seen in nonhuman primates, our closest phylogenetic relatives. We propose that comparative studies can provide insight into four major questions about the nature of human choice biases that cannot be addressed by studies of our species alone. First, research with other primates can address the evolution of human choice biases and identify shared versus human-unique tendencies in decision making. Second, primate studies can constrain hypotheses about the psychological mechanisms underlying such biases. Third, comparisons of closely related species can identify when distinct mechanisms underlie related biases by examining evolutionary dissociations in choice strategies. Finally, comparative work can provide insight into the biological rationality of economically irrational preferences.
Rosati, A. G., Wobber, V., Hughes, K., & Santos, L. R. (2014). Comparative developmental psychology: How is human cognitive development unique?. Evolutionary Psychology, 12, 448-473. [PDF] [Publisher’s Version] Abstract
The fields of developmental and comparative psychology both seek to illuminate the roots of adult cognitive systems. Developmental studies target the emergence of adult cognitive systems over ontogenetic time, whereas comparative studies investigate the origins of human cognition in our evolutionary history. Despite the long tradition of research in both of these areas, little work has examined the intersection of the two: the study of cognitive development in a comparative perspective. In the current article, we review recent work using this comparative developmental approach to study non-human primate cognition. We argue that comparative data on the pace and pattern of cognitive development across species can address major theoretical questions in both psychology and biology. In particular, such integrative research will allow stronger biological inferences about the function of developmental change, and will be critical in addressing how humans come to acquire species-unique cognitive abilities.
Rosati, A. G., Rodriguez, K., & Hare, B. (2014). The ecology of spatial memory in four lemur species. Animal Cognition, 17, 947-961. [PDF] [Supplementary] [Videos] [Publisher’s Version] Abstract
Evolutionary theories suggest that ecology is a major factor shaping cognition in primates. However, there have been few systematic tests of spatial memory abilities involving multiple primate species. Here, we examine spatial memory skills in four strepsirrhine primates that vary in level of frugivory: ruffed lemurs (Varecia sp.), ring-tailed lemurs (Lemur catta), mongoose lemurs (Eulemur mongoz), and Coquerel’s sifakas (Propithecus coquereli). We compare these species across three studies targeting different aspects of spatial memory: recall after a long-delay, learning mechanisms supporting memory and recall of multiple locations in a complex environment. We find that ruffed lemurs, the most frugivorous species, consistently showed more robust spatial memory than the other species across tasks—especially in comparison with sifakas, the most folivorous species. We discuss these results in terms of the importance of considering both ecological and social factors as complementary explanations for the evolution of primate cognitive skills.
Rosati, A. G., & Hare, B. (2013). Chimpanzees and bonobos exhibit emotional reactions to decision outcomes. PLoS One, 8 e63058. [PDF] [Supplementary] [Videos] [Publisher’s Version] Abstract
The interface between cognition, emotion, and motivation is thought to be of central importance in understanding complex cognitive functions such as decision-making and executive control in humans. Although nonhuman apes have complex repertoires of emotional expression, little is known about the role of affective processes in ape decision-making. To illuminate the evolutionary origins of human-like patterns of choice, we investigated decision-making in humans’ closest phylogenetic relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). In two studies, we examined these species’ temporal and risk preferences, and assessed whether apes show emotional and motivational responses in decision making contexts. We find that (1) chimpanzees are more patient and more risk-prone than are bonobos, (2) both species exhibit affective and motivational responses following the outcomes of their decisions, and (3) some emotional and motivational responses map onto species-level and individual-differences in decision-making. These results indicate that apes do exhibit emotional responses to decision-making, like humans. We explore the hypothesis that affective and motivational biases may underlie the psychological mechanisms supporting value-based preferences in these species.
Rosati, A. G., Herrmann, E., Kaminski, J., Krupenye, C., Melis, A. P., Schroepfer, K., Tan, J., et al. (2013). Assessing the psychological health of captive and wild apes: A response to Ferdowsian et al. (2011). Journal of Comparative Psychology, 127, 329–336. [PDF] [Publisher’s Version] Abstract
As many studies of cognition and behavior involve captive animals, assessing any psychological impact of captive conditions is an important goal for comparative researchers. Ferdowsian and colleagues (2011) sought to address whether captive chimpanzees show elevated signs of psychopathology relative to wild apes. They modified a checklist of diagnostic criteria for major depression and posttraumatic stress disorder in humans, and applied these criteria to various captive and wild chimpanzee populations. We argue that measures derived from human diagnostic criteria are not a powerful tool for assessing the psychological health of nonverbal animals. In addition, we highlight certain methodological drawbacks of the specific approach used by Ferdowsian and colleagues (2011). We propose that research should (1) focus on objective behavioral criteria that account for species-typical behaviors and can be reliably identified across populations; (2) account for population differences in rearing history when comparing how current environment impacts psychological health in animals; and (3) focus on how changes in current human practices can improve the well-being of both captive and wild animals.
Rosati, A. G., & Hare, B. (2012). Chimpanzees and bonobos exhibit divergent spatial memory development. Developmental Science, 15, 840-853. [PDF] [Publisher’s Version] Abstract
Spatial cognition and memory are critical cognitive skills underlying foraging behaviors for all primates. While the emergence of these skills has been the focus of much research on human children, little is known about ontogenetic patterns shaping spatial cognition in other species. Comparative developmental studies of nonhuman apes can illuminate which aspects of human spatial development are shared with other primates, versus which aspects are unique to our lineage. Here we present three studies examining spatial memory development in our closest living relatives, chimpanzees (Pan troglodytes) and bonobos (P. paniscus). We first compared memory in a naturalistic foraging task where apes had to recall the location of resources hidden in a large outdoor enclosure with a variety of landmarks (studies 1 and 2). We then compared older apes using a matched memory choice paradigm (study 3). We found that chimpanzees exhibited more accurate spatial memory than bonobos across contexts, supporting predictions from these species’ different feeding ecologies. Furthermore, chimpanzees—but not bonobos—showed developmental improvements in spatial memory, indicating that bonobos exhibit cognitive paedomorphism (delays in developmental timing) in their spatial abilities relative to chimpanzees. Together, these results indicate that the development of spatial memory may differ even between closely related species. Moreover, changes in the spatial domain can emerge during nonhuman ape ontogeny, much like some changes seen in human children.
Rosati, A. G., & Hare, B. (2012). Decision-making across social contexts: competition increases preferences for risk in chimpanzees and bonobos. Animal Behaviour, 84, 869-879. [PDF] [Supplementary] [Publisher’s Version] Abstract
Context can have a powerful influence on decision-making strategies in humans. In particular, people sometimes shift their economic preferences depending on the broader social context, such as the presence of potential competitors or mating partners. Despite the important role of competition in primate conspecific interactions, as well as evidence that competitive social contexts impact primates’ social cognitive skills, there has been little study of how social context influences the strategies that nonhumans show when making decisions about the value of resources. Here we investigate the impact of social context on preferences for risk (variability in payoffs) in our two closest phylogenetic relatives, chimpanzees, Pan troglodytes, and bonobos, Pan paniscus. In a first study, we examine the impact of competition on patterns of risky choice. In a second study, we examine whether a positive play context affects risky choices. We find that (1) apes are more likely to choose the risky option when making decisions in a competitive context; and (2) the play context did not influence their risk preferences. Overall these results suggest that some types of social contexts can shift patterns of decision making in nonhuman apes, much like in humans. Comparative studies of chimpanzees and bonobos can therefore help illuminate the evolutionary processes shaping human economic behaviour.
Warneken, F., & Rosati, A. G. (2012). Early social cognition: How psychological mechanism can inform models of decision-making. In: Evolving the Mechanisms of Decision Making: Toward a Darwinian Decision Theory, Strüngmann Forum Reports, vol. 11 (P. Hammerstein and J. R. Stevens, eds.). Cambridge, MA: MIT Press, pp. 288-289. [PDF] [Publisher’s Version.] Abstract
Many approaches to understanding social decision-making use formalized models that account for costs and benefits to predict how individuals should choose. While these types of models are appropriate for describing social behavior at the ultimate level—accounting for the fitness consequences of different patterns of behavior—they do not necessarily reflect the proximate mechanisms used by decision-makers. We argue that a focus on psychological mechanisms is essential for understanding the causes of decision making in a social context. We particularly focus on the behavior of human children to elucidate the psychological capacities that are foundational for the developmental emergence of social decision-making in humans. In particular, we present evidence that across a wide range of contexts, young children appear to focus on the underlying psychological states of potential social partners in cooperative contexts. This suggests that many types of social decisions may be driven by intention-attribution, not explicit utility calculations. We propose that a comprehensive theory of social decision-making has to address both questions about ultimate function, as well as integrate empirical studies of the psychological instantiation of these processes. Developmental approaches are particularly informative, as they elucidate the origins of decision-making, as well as the factors that shape them into their mature form seen in adults.
MacLean, E., Matthews, L. J., Hare, B., Nunn, C. L., Anderson, R. C., Aureli, F., Brannon, E., et al. (2012). How does cognition evolve? Phylogenetic comparative psychology. Animal Cognition, 15, 223-238. [PDF] [Publisher’s Version] Abstract
Now more than ever animal studies have the potential to test hypotheses regarding how cognition evolves. Comparative psychologists have developed new techniques to probe the cognitive mechanisms underlying animal behavior, and they have become increasingly skillful at adapting methodologies to test multiple species. Meanwhile, evolutionary biologists have generated quantitative approaches to investigate the phylogenetic distribution and function of phenotypic traits, including cognition. In particular, phylogenetic methods can quantitatively (1) test whether specific cognitive abilities are correlated with life history (e.g., lifespan), morphology (e.g., brain size), or socio-ecological variables (e.g., social system), (2) measure how strongly phylogenetic relatedness predicts the distribution of cognitive skills across species, and (3) estimate the ancestral state of a given cognitive trait using measures of cognitive performance from extant species. Phylogenetic methods can also be used to guide the selection of species comparisons that offer the strongest tests of a priori predictions of cognitive evolutionary hypotheses (i.e., phylogenetic targeting). Here, we explain how an integration of comparative psychology and evolutionary biology will answer a host of questions regarding the phylogenetic distribution and history of cognitive traits, as well as the evolutionary processes that drove their evolution.
Rosati, A. G., & Hare, B. (2011). Chimpanzees and bonobos distinguish between risk and ambiguity. Biology Letters, 7 15-18. [PDF] [Supplementary] [Publisher’s Version] Abstract
Although recent research has investigated animal decision-making under risk, little is known about how animals choose under conditions of ambiguity when they lack information about the available alternatives. Many models of choice behaviour assume that ambiguity does not impact decision-makers, but studies of humans suggest that people tend to be more averse to choosing ambiguous options than risky options with known probabilities. To illuminate the evolutionary roots of human economic behaviour, we examined whether our closest living relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), share this bias against ambiguity. Apes chose between a certain option that reliably provided an intermediately preferred food type, and a variable option that could vary in the probability that it provided a highly preferred food type. To examine the impact of ambiguity on ape decision-making, we interspersed trials in which chimpanzees and bonobos had no knowledge about the probabilities. Both species avoided the ambiguous option compared with their choices for a risky option, indicating that ambiguity aversion is shared by humans, bonobos and chimpanzees.
Schroepfer, K. K., Rosati, A. G., Chartrand, T., & Hare, B. (2011). Use of “entertainment” chimpanzees in commercials distorts public perception regarding their conservation status. PLoS One, 6 e26048. [PDF] [Publisher’s Version] Abstract
Chimpanzees (Pan troglodytes) are often used in movies, commercials and print advertisements with the intention of eliciting a humorous response from audiences. The portrayal of chimpanzees in unnatural, human-like situations may have a negative effect on the public’s understanding of their endangered status in the wild while making them appear as suitable pets. Alternatively, media content that elicits a positive emotional response toward chimpanzees may increase the public’s commitment to chimpanzee conservation. To test these competing hypotheses, participants (n = 165) watched a series of commercials in an experiment framed as a marketing study. Imbedded within the same series of commercials was one of three chimpanzee videos. Participants either watched 1) a chimpanzee conservation commercial, 2) commercials containing ‘‘entertainment’’ chimpanzees or 3) control footage of the natural behavior of wild chimpanzees. Results from a post- viewing questionnaire reveal that participants who watched the conservation message understood that chimpanzees were endangered and unsuitable as pets at higher levels than those viewing the control footage. Meanwhile participants watching commercials with entertainment chimpanzees showed a decrease in understanding relative to those watching the control footage. In addition, when participants were given the opportunity to donate part of their earnings from the experiment to a conservation charity, donations were least frequent in the group watching commercials with entertainment chimpanzees. Control questions show that participants did not detect the purpose of the study. These results firmly support the hypothesis that use of entertainment chimpanzees in the popular media negatively distorts the public’s perception and hinders chimpanzee conservation efforts.
Stevens, J. R., Rosati, A. G., Heilbronner, S. R., & Mueloff, N. (2011). Waiting for grapes: Expectancy and delayed gratification in bonobos. International Journal of Comparative Psychology, 24, 99-111. [PDF] [Publisher’s Version] Abstract
Responses to delayed rewards vary widely across individuals and have important implications for personality and temperament. Animals may avoid delayed rewards because the future is uncertain. Therefore, expectations about receiving a future reward should influence the response to delayed payoffs. Here, we offered bonobos (Pan paniscus) a delayed gratification task in which food accumulated over time. Once subjects chose to consume the reward, food stopped accumulating. We tested their willingness to wait with a reliable and an unreliable experimenter to vary the subjects’ expectations that they would receive the food. Subjects waited less often with the unreliable experimenter but showed individual differences in the degree to which reliability generalized across experimental tasks. These data suggest that the expectations generated about the likelihood of receiving future rewards influence how individuals balance current and future needs.
Hare, B., Rosati, A. G., Kaminski, J., Braeuer, J., Call, J., & Tomasello, M. (2010). The domestication hypothesis for dogs’ skills with human communication: a response to Udell et al. (2008) and Wynne et al. (2008). Animal Behaviour, 79, e1-e6. Publisher’s Version. PDF. Abstract
Domestic dogs have special skills in comprehending human communicative behaviours. Dogs across a range of breeds use human communicative cues such as pointing or physical markers to find food that is hidden in one of two hiding places. Wolves, in contrast, do not readily exhibit this ability, suggesting that domestication may have shaped the expression of these skills in dogs. Recently, two papers challenge the ideas (1) that dogs outperform wolves in using human communicative gestures (Udell et al. 2008) and (2) that dogs require very limited human exposure to show initial skill in using such communicative cues (Wynne et al. 2008). To evaluate the evidence presented in these studies, we first discuss several methodological concerns that we have about the approach of Udell et al. (2008), then we reanalyse their data based on these methodological concerns. We also present a test of shelter dogs naıve to cognitive testing to examine whether it is the case that shelter dogs are less skilled at using human communicative cues than other groups of dogs. Finally, we directly rebut the critique of Wynne et al. (2008) and argue that there remains no evidence of significant differences in performance between dogs of different ages in their use of human communicative cues. We conclude that the domestication hypothesis remains the best explanation for dogs’ special skills for communicating with humans.
Rosati, A. G., Santos, L. R., & Hare, B. (2010). Primate social cognition: thirty years after Premack and Woodruff. In: Primate Neuroethology (A. Ghazanfar and M. Platt, eds.). Oxford: Oxford University Press, pp. 117-143. [PDF] [Publisher’s Version] Abstract
Since Darwin declared the mind as the province of biology as well as psychology, the human intellect has been a major challenge for evolutionary biologists, with some researchers emphasizing the continuity between humans and other animals, and others emphasizing seemingly unique aspects of our psychological makeup. Research over the past ten years has revealed that at least some primates have some capability to assess the psychological states of others—while simultaneously showing striking differences between the social-cognitive capacities of humans and other primates. Here we address two aspects of primate social cognition—understanding of intentional, goal-directed action, and understanding perceptions, knowledge, and beliefs—focusing on newest comparative research since the last major reviews were written on the topic over a decade ago. We first review evidence suggesting that diverse species of primates understand the actions of others in terms of goals and intentions, and furthermore can reason about some, but probably not all, kinds of psychological states. We then examine the hypothesis that primates show their most complex social skills in competitive contexts, and suggest that inquiry into other aspects of primate social life, such as during cooperative interactions, may prove to be the next important step for experimental inquiries into primate social-cognitive skills. Finally, we examine primate social cognition in a broader evolutionary context that may allow us to better understand both primate and human cognitive skills.
Rosati, A. G., & Hare, B. (2010). Social cognition: from behavior-reading to mind-reading. In: The Encyclopedia of Behavioral Neuroscience (G. Koob, R. F. Thompson, & M. L. Moal, Eds.). Elsevier, pp. 263-268. Publisher’s Version. PDF. Abstract
The social world has long been thought to be a major force shaping primate cognition: the social lives of primates are thought to be sufficiently complex to have acted as a driving force in primate cognitive evolution. This basic thesis – that the sophisticated cognitive abilities of primates have evolved for a social function – has spurred experimental and theoretical investigations for over 40 years. In this article, we highlight a selection of complex behaviors that primates exhibit when interacting with others, with special attention to the cognitive mechanisms supporting those behaviors. Fundamental to the study of comparative cognition is the idea that many species may exhibit behaviors that appear similar, even though the psychology underlying those behaviors may differ across taxa. This distinction highlights the importance of thinking about primate social interactions not only in the context of behavioral evolution – the special things that primates (and humans) do – but also in terms of cognitive evolution – the special ways that primates think. We use this framework to analyze primate social behavior, and the differing psychologies underlying this behavior, in three areas: gaze-following, food competition, and mutualistic cooperation. The ultimate challenge of such analyses will be to understand why such different cognitive mechanisms have evolved across species.
Rosati, A. G., & Stevens, J. R. (2009). The adaptive nature of context-dependent choice. In: Rational Animal, Irrational Human (S. Watanabe, A. Young, A. Blaisdell, & Y. Yamazaki, Eds.) Tokyo: Keio University Press, pp. 101-117. Publisher’s Version.PDF. Abstract
Although classical economic theory hinges on the assumption that rational actors should seek to maximize gains, psychologists and behavioral economists have recently collected a wealth of evidence challenging this premise. In violation of the principles of rational choice, context appears to dramatically influence human decision making. Like humans, numerous nonhuman animals, ranging from honeybees to primates, are sensitive to context, suggesting deep evolutionary roots for seemingly irrational decision-making. Many psychologists have suggested that such choices may stem from cognitive biases that result in errors. We contend, however, that labeling context-dependent choices as errors obscures the real issue. Natural selection does not create organisms that adhere to economic theory—it creates decision makers that maximize fitness. We review evidence that many species show context-dependence when making decisions and then present a framework for analyzing the adaptive consequences of these choices. We argue for an approach weaving psychological perspectives into an evolutionary framework to elucidate the nature of decision making.
Rosati, A. G., & Hare, B. (2009). Looking past the model species: diversity in gaze-following skills across primates. Current Opinion in Neurobiology, 19, 45-51. Publisher’s Version. PDF. Abstract
Primates must navigate complex social landscapes in their daily lives: gathering information from and about others, competing with others for food and mates, and cooperating to obtain rewards as well. Gaze-following often provides important clues as to what others see, know, or will do; using information about social attention is thus crucial for primates to be competent social actors. However, the cognitive bases of the gaze-following behaviors that primates exhibit appear to vary widely across species. The ultimate challenge of such analyses will therefore be to understand why such different cognitive mechanisms have evolved across species.
Venkatraman, V., Rosati, A. G., Taren, A., & Huettell, S. (2009). Resolving response, decision and strategic control: Evidence for a functional topography in dorsomedial prefrontal cortex. Journal of Neuroscience, 29, 13158-13164. Publisher’s Version. PDF. Supplementary Material. Abstract
The dorsomedial prefrontal cortex (DMPFC) plays a central role in aspects of cognitive control and decision making. Here, we provide evidence for an anterior-to-posterior topography within the DMPFC using tasks that evoke three distinct forms of control demands— response, decision, and strategic— each of which could be mapped onto independent behavioral data. Specifically, we identify three spatially distinct regions within the DMPFC: a posterior region associated with control demands evoked by multiple incompatible responses, a middle region associated with control demands evoked by the relative desirability of decision options, and an anterior region that predicts control demands related to deviations from an individual’s preferred decision-making strategy. These results provide new insight into the functional organization of DMPFC and suggest how recent controversies about its role in complex decision making and response mapping can be reconciled.
2008 and earlier
Heilbronner, S. R., Rosati, A. G., Stevens, J. R., Hare, B., & Hauser, M. D. (2008). A fruit in the hand or two in the bush? Divergent risk preferences in chimpanzees and bonobos. Biology Letters, 4 246-249. Publisher’s Version. PDF. Supplementary Material. Abstract
Human and non-human animals tend to avoid risky prospects. If such patterns of economic choice are adaptive, risk preferences should reflect the typical decision-making environments faced by organisms. However, this approach has not been widely used to examine the risk sensitivity in closely related species with different ecologies. Here, we experimentally examined risk-sensitive behaviour in chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), closely related species whose distinct ecologies are thought to be the major selective force shaping their unique behavioural repertoires. Because chimpanzees exploit riskier food sources in the wild, we predicted that they would exhibit greater tolerance for risk in choices about food. Results confirmed this prediction: chimpanzees significantly preferred the risky option, whereas bonobos preferred the fixed option. These results provide a relatively rare example of risk-prone behaviour in the context of gains and show how ecological pressures can sculpt economic decision making.
Rosati, A. G., Stevens, J. R., Hare, B., & Hauser, M. D. (2007). The evolutionary origins of human patience: Temporal preferences in chimpanzees, bonobos, and human adults. Current Biology, 17, 1663–1668. Publisher’s Version. PDF. Supplementary Material. Study Videos. Commentary.Abstract
To make adaptive choices, individuals must sometimes exhibit patience, forgoing immediate benefits to acquire more valuable future rewards. Although humans account for future consequences when making temporal decisions, many animal species wait only a few seconds for delayed benefits. Current research thus suggests a phylogenetic gap between patient humans and impulsive, present-oriented animals, a distinction with implications for our understanding of economic decision making and the origins of human cooperation. On the basis of a series of experimental results, we reject this conclusion. First, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) exhibit a degree of patience not seen in other animals tested thus far. Second, humans are less willing to wait for food rewards than are chimpanzees. Third, humans are more willing to wait for monetary rewards than for food, and show the highest degree of patience only in response to decisions about money involving low opportunity costs. These findings suggest that core components of the capacity for future-oriented decisions evolved before the human lineage diverged from apes. Moreover, the different levels of patience that humans exhibit might be driven by fundamental differences in the mechanisms representing biological versus abstract rewards.
Rosati, A. G., Stevens, J. R., & Hauser, M. D. (2006). The effect of handling time on temporal discounting in two New World primates. Animal Behaviour, 71, 1379-1387. Publisher’s Version. PDF. Abstract
Foraging decisions in nonhuman animals often require choosing between small, immediate food rewards and larger, more delayed rewards. Faced with such choices, animals typically discount or devalue the future quite strongly. Although discounting studies often focus on delays to reward access, other temporal intervals contribute to foraging rate, and thus may potentially influence discounting levels. Here, we examine the effect of handling time, the time required to process and consume food, on discounting in cottontop tamarins, Saguinus oedipus, and common marmosets, Callithrix jacchus, two species that differ in levels of temporal discounting. We presented subjects with a discounting task under two conditions. In the first condition, we made the entire reward available after the delay expired. In the second condition, we experimentally increased the minimum length of time required to consume the reward to simulate a longer handling time. We found that tamarins and marmosets showed sensitivity to increases in the time necessary to process food rewards. Both species adjusted their preferences to account for different handling times at long delays to accessing food. Consequently, models of discounting behaviour that include handling times may better describe animal choices than models that focus exclusively on delays prior to access.
Santos, L. R., Rosati, A. G., Spaulding, B., Sproul, C., & Hauser, M. D. (2005). Means-means-end tool choice in cotton-top tamarins (Sanguinus oedipus): finding the limits on primates’ knowledge of tools. Animal Cognition, 8 236-246. Publisher’s Version. PDF. Abstract
Most studies of animal tool use require subjects to use one object to gain access to a food reward. In many real world situations, however, animals perform more than one action in sequence to achieve their goals. Of theoretical interest is whether animals have the cognitive capacity to recognize the relationship between consecutive action sequences in which there may be one overall goal and several subgoals. Here we ask if cotton-top tamarins, a species that in captivity uses tools to solve means-end problems, can go one step further and use a sequence of tools (means) to obtain food (end). We first trained subjects to use a pulling tool to obtain a food reward. After this initial training, subjects were presented with problems in which one tool had to be used in combination with a second in order to obtain food. Subjects showed great difficulty when two tools were required to obtain the food reward. Although subjects attended to the connection between the tool and food reward, they ignored the physical connection between the two tools. After training on a two-tool problem, we presented subjects with a series of transfer tests to explore if they would generalize to new types of connections between the tools. Subjects readily transferred to new connections. Our results therefore provide the first evidence to date that tamarins can learn to solve problems involving two tools, but that they do so only with sufficient training.
Stevens, J. R., Rosati, A. G., Ross, K. R., & Hauser, M. D. (2005). Will travel for food: Spatial discounting in two New World monkeys. Current Biology, 15, 1855–1860. Publisher’s Version. PDF. Supplementary Material. Commentary. Abstract
Nonhuman animals steeply discount the future, showing a preference for small, immediate over large, delayed rewards. Currently unclear is whether discounting functions depend on context. Here, we examine the effects of spatial context on discounting in cotton-top tamarins (Saguinus oedipus) and common marmosets (Callithrix jacchus), species known to differ in temporal discounting. We presented subjects with a choice between small, nearby rewards and large, distant rewards. Tamarins traveled farther for the large reward than marmosets, attending to the ratio of reward differences rather than their absolute values. This species difference contrasts with performance on a temporal task in which marmosets waited longer than tamarins for the large reward. These comparative data indicate that context influences choice behavior, with the strongest effect seen in marmosets who discounted more steeply over space than over time. These findings parallel details of each species’ feeding ecology. Tamarins range over large distances and feed primarily on insects, which requires using quick, impulsive action. Marmosets range over shorter distances than tamarins and feed primarily on tree exudates, a clumped resource that requires patience to wait for sap to exude. These results show that discounting functions are context specific, shaped by a history of ecological pressures.