Endowment effects in chimpanzees

Right thalamic volume mediates impact of the dopamine beta-hydroxylase gene on the endowment effect

The endowment effect is a tendency that individuals overvalue items belonging to them relative to those items that do not. Previous studies showed a strong relation between the dopamine beta-hydroxylase (DBH) gene and the endowment effect (EE), and a link between EE and task-based functional MRI activation in multiple brain regions. However, the role of brain structure on EE remains unclear. In this study, we have explored whether regional brain volume mediate the effect of the DBH gene on EE. Results showed that rs1611115, single-nucleotide polymorphisms (SNPs) at DBH loci, were significantly associated with right thalamus volume and the endowment effect in males but not in female participants. Specifically, male DBH rs1611115 T-carriers had larger right thalamus volume compared to carriers of CC genotype and exhibited a greater endowment effect. Importantly, we found that right thalamus volume mediated the effect of rs1611115 on the endowment effect in male participants. This study demonstrated how thalamic volume plays an important mediating role between genetics and decision-making in humans.

How can I find what I want? Can children, chimpanzees and capuchin monkeys form abstract representations to guide their behavior in a sampling task?

concepts are a powerful tool for making wide-ranging predictions in new situations based on little experience. Whereas looking-time studies suggest an early emergence of this ability in human infancy, other paradigms like the relational match to sample task often fail to detect abstract concepts until late preschool years. Similarly, non-human animals show difficulties and often succeed only after long training regimes. Given the considerable influence of slight task modifications, the conclusiveness of these findings for the development and phylogenetic distribution of abstract reasoning is debated. Here, we tested the abilities of 3 to 5-year-old children, chimpanzees, and capuchin monkeys in a unified and more ecologically valid task design based on the concept of "overhypotheses" (Goodman, 1955). Participants sampled high- and low-valued items from containers that either each offered items of uniform value or a mix of high- and low-valued items. In a test situation, participants should switch away earlier from a container offering low-valued items when they learned that, in general, items within a container are of the same type, but should stay longer if they formed the overhypothesis that containers bear a mix of types. We compared each species' performance to the predictions of a probabilistic hierarchical Bayesian model forming overhypotheses at a first and second level of abstraction, adapted to each species' reward preferences. Children and, to a more limited extent, chimpanzees demonstrated their sensitivity to abstract patterns in the evidence. In contrast, capuchin monkeys did not exhibit conclusive evidence for the ability of abstract knowledge formation.

The missing link? How do non-human primates fit in the minimalist model of ownership?

Can Boyer's model of ownership psychology provide useful insights for comparative research? I apply his model to argue that we currently have evidence for possession psychology (based on competitive resource acquisition) in non-human primates, but not for ownership psychology.

The art of the deal: Deciphering the endowment effect from traders' eyes

People are often reluctant to trade, a reticence attributed to the endowment effect. The prevailing account attributes the endowment effect to valuation-related bias, manifesting as sellers valuing goods more than buyers, whereas an alternative account attributes it to response-related bias, manifesting as both buyers and sellers tending to stick to the status quo. Here, by tracking and modeling eye activity of buyers and sellers during trading, we accommodate both views within an evidence-accumulation framework. We find that valuation-related bias is indexed by asymmetric attentional allocation between buyers and sellers, whereas response-related bias is indexed by arousal-linked pupillary reactivity. A deal emerges when both buyers and sellers attend to their potential gains and dilate their pupils. Our study provides preliminary evidence for our computational framework of the dynamic processes mediating the endowment effect and identifies physiological biomarkers of deal-making.

Comparative economics: how studying other primates helps us better understand the evolution of our own economic decision making

The origins of evolutionary games are rooted in both economics and animal behaviour, but economics has, until recently, focused primarily on humans. Although historically, specific games were used in targeted circumstances with non-human species (i.e. the Prisoner's Dilemma), experimental economics has been increasingly recognized as a valuable method for directly comparing both the outcomes of economic decisions and their underlying mechanisms across species, particularly in comparison with humans, thanks to the structured procedures that allow for them to be instantiated across a variety of animals. So far, results in non-human primates suggest that even when outcomes are shared, underlying proximate mechanisms can vary substantially. Intriguingly, in some contexts non-human primates more easily find a Nash equilibrium than do humans, possibly owing to their greater willingness to explore the parameter space, but humans excel at more complex outcomes, such as alternating between two Nash equilibria, even when deprived of language or instruction, suggesting potential mechanisms that humans have evolved to allow us to solve complex social problems. We consider what these results suggest about the evolution of economic decision-making and suggest future directions, in particular the need to expand taxonomic diversity, to expand this promising approach. This article is part of the theme issue 'Half a century of evolutionary games: a synthesis of theory, application and future directions'.

Rationality and cognitive bias in captive gorillas' and orang-utans' economic decision-making

Human economic decision-making sometimes appears to be irrational. Partly, this is due to cognitive biases that can lead to suboptimal economic choices and context-dependent risk-preferences. A pertinent question is whether such biases are part of our evolutionary heritage or whether they are culturally acquired. To address this, we tested gorillas (Gorilla gorilla gorilla) and orang-utans (Pongo abelii) with two risk-assessment experiments that differed in how risk was presented. For both experiments, we found that subjects increased their preferences for the risky options as their expected gains increased, showing basic understanding of reward contingencies and rational decision-making. However, we also found consistent differences in risk proneness between the two experiments, as subjects were risk-neutral in one experiment and risk-prone in the other. We concluded that gorillas and orang-utans are economically rational but that their decisions can interact with pre-existing cognitive biases which modulates their risk-preference in context-dependent ways, explaining the variability of their risk-preference in previous literature.

Rethinking Rationality

We seek to understand rational decision making and if it exists whether finite (bounded) agents may be able to achieve its principles. This aim has been a singular objective throughout much of human science and philosophy, with early discussions identified since antiquity. More recently, there has been a thriving debate based on differing perspectives on rationality, including adaptive heuristics, Bayesian theory, quantum theory, resource rationality, and probabilistic language of thought. Are these perspectives on rationality mutually exclusive? Are they all needed? Do they undermine an aim to have rational standards in decision situations like politics, medicine, legal proceedings, and others, where there is an expectation and need for decision making as close to "optimal" as possible? This special issue brings together representative contributions from the currently predominant views on rationality, with a view to evaluate progress on these and related questions.

Tools of the trade: the bio-cultural evolution of the human propensity to trade

Humans are standouts in their propensity to trade. More specially, the kind of trading found in humans-featuring the exchange of many different goods and services with many different others, for the mutual benefit of all the involved parties-far exceeds anything that is found in any other creature. However, a number of important questions about this propensity remain open. First, it is not clear exactly what makes this propensity so different in the human case from that of other animals. Second, it is not clear why other animals did not acquire this propensity to the extent that humans did. Third, it is not clear what explains the fact that the extent to which humans engage in trade is culturally highly variable. The paper argues that at the heart of the human-animal divergence in this propensity is the particular socio-cultural environment in which humans evolved. This has led them to sometimes, but not always, acquire the cognitive technology (writing, algebra, tallying devices, money, etc.) to support a sophisticated disposition and capacity for reciprocal cooperation, and deep and wide concepts of property and exchange value.

Psychiatric Neural Networks and Precision Therapeutics by Machine Learning

Learning and environmental adaptation increase the likelihood of survival and improve the quality of life. However, it is often difficult to judge optimal behaviors in real life due to highly complex social dynamics and environment. Consequentially, many different brain regions and neuronal circuits are involved in decision-making. Many neurobiological studies on decision-making show that behaviors are chosen through coordination among multiple neural network systems, each implementing a distinct set of computational algorithms. Although these processes are commonly abnormal in neurological and psychiatric disorders, the underlying causes remain incompletely elucidated. Machine learning approaches with multidimensional data sets have the potential to not only pathologically redefine mental illnesses but also better improve therapeutic outcomes than DSM/ICD diagnoses. Furthermore, measurable endophenotypes could allow for early disease detection, prognosis, and optimal treatment regime for individuals. In this review, decision-making in real life and psychiatric disorders and the applications of machine learning in brain imaging studies on psychiatric disorders are summarized, and considerations for the future clinical translation are outlined. This review also aims to introduce clinicians, scientists, and engineers to the opportunities and challenges in bringing artificial intelligence into psychiatric practice.

Non-human primate token use shows possibilities but also limitations for establishing a form of currency

Non-human primates evaluate choices based on quantitative information and subjective valuation of options. Non-human primates can learn to value tokens as placeholders for primary rewards (such as food). With those tokens established as a potential form of 'currency', it is then possible to examine how they respond to opportunities to earn and use tokens in ways such as accumulating tokens or exchanging tokens with each other or with human experimenters to gain primary rewards. Sometimes, individuals make efficient and beneficial choices to obtain tokens and then exchange them at the right moments to gain optimal reward. Sometimes, they even accumulate such rewards through extended delay of gratification, or through other exchange-based interactions. Thus, non-human primates are capable of associating value to arbitrary tokens that may function as currency-like stimuli, but there also are strong limitations on how non-human primates can integrate such tokens into choice situations or use such tokens to fully 'symbolize' economic decision-making. These limitations are important to acknowledge when considering the evolutionary emergence of currency use in our species. This article is part of the theme issue 'Existence and prevalence of economic behaviours among non-human primates'.

What behaviour in economic games tells us about the evolution of non-human species' economic decision-making behaviour

In the past decade, there has been a surge of interest in using games derived from experimental economics to test decision-making behaviour across species. In most cases, researchers are using the games as a tool, for instance, to understand what factors influence decision-making, how decision-making differs across species or contexts, or to ask broader questions about species' propensities to cooperate or compete. These games have been quite successful in this regard. To what degree, however, do these games tap into species' economic decision-making? For the purpose of understanding the evolution of economic systems in humans, this is the key question. To study this, we can break economic decision-making down into smaller components, each of which is a potential step in the evolution of human economic behaviour. We can then use data from economic games, which are simplified, highly structured models of decision-making and therefore ideal for the comparative approach, to directly compare these components across species and contexts, as well as in relation to more naturalistic behaviours, to better understand the evolution of economic behaviour and the social and ecological contexts that influenced it. The comparative approach has successfully informed us about the evolution of other complex traits, such as language and morality, and should help us more deeply understand why and how human economic systems evolved. This article is part of the theme issue 'Existence and prevalence of economic behaviours among non-human primates'.

Economics and Epicycles

I aver that standard economics as a model of human behavior is as incorrect in 2017 (after Thaler) as geocentrism was as a model of celestial behavior in 1617 (after Galileo). Behavioral economic studies that have exposed the paradoxes and anomalies in standard economics are akin to epicycles on geocentrism. Just as no amount of epicycles could salvage geocentrism as a model of celestial behavior because it was fundamentally incorrect, no amount of behavioral economic adjustments could salvage standard economics as a model of human behavior because it is fundamentally incorrect. Many of the cognitive biases exhibited by humans are shared by other species, so not only are human actors Humans (as opposed to Econs), but nonhuman animals as phylogenetically distant from humans as ants and locusts are also Humans. Evolutionary biology as a model of human behavior can explain many of the hitherto unexplained cognitive biases and provide a unifying model of human behavior currently lacking in behavioral economics.

Decomposing loss aversion from gaze allocation and pupil dilation

Loss-averse decisions, in which one avoids losses at the expense of gains, are highly prevalent. However, the underlying mechanisms remain controversial. The prevailing account highlights a valuation bias that overweighs losses relative to gains, but an alternative view stresses a response bias to avoid choices involving potential losses. Here we couple a computational process model with eye-tracking and pupillometry to develop a physiologically grounded framework for the decision process leading to accepting or rejecting gambles with equal odds of winning and losing money. Overall, loss-averse decisions were accompanied by preferential gaze toward losses and increased pupil dilation for accepting gambles. Using our model, we found gaze allocation selectively indexed valuation bias, and pupil dilation selectively indexed response bias. Finally, we demonstrate that our computational model and physiological biomarkers can identify distinct types of loss-averse decision makers who would otherwise be indistinguishable using conventional approaches. Our study provides an integrative framework for the cognitive processes that drive loss-averse decisions and highlights the biological heterogeneity of loss aversion across individuals.

Behaviour of nonhuman primate mothers toward their dead infants: uncovering mechanisms

In comparative thanatology, most reports for nonhuman mammals concern mothers' behavioural responses to their dead offspring: most prominently, dead-infant carrying (sometimes of extended duration); but also inspection, proximity, maternal care such as grooming, protective behaviours and filial cannibalism. Documented across many primate species, these behaviours remain poorly understood in all. The literature is dominated by relatively brief qualitative descriptions of isolated anecdotal cases in apes and monkeys. We argue for quantitative coding in case reports, alongside analyses of longitudinal records of such events to allow objective evaluation of competing theories, and systematic comparisons within and across species and populations. Obtaining necessary datasets depends on raised awareness in researchers of the importance of recording occurrences and knowledge of pertinent data to collect. We review proposed explanatory hypotheses and outline data needed to test each empirically. To determine factors influencing infant-corpse carriage, we suggest analyses of deaths resulting in 'carry' versus 'no carry'. For individual cases, we highlight behavioural variables to code and the need for hormonal samples. We discuss mothers' stress and welfare in relation to infant death, continued transportation and premature removal of the corpse. Elucidating underlying proximate and ultimate causes is important for understanding phylogeny of maternal responses to infant death.This article is part of the theme issue 'Evolutionary thanatology: impacts of the dead on the living in humans and other animals'.

Children, but not great apes, respect ownership

Access to and control of resources is a major source of costly conflicts. Animals, under some conditions, respect what others control and use (i.e. possession). Humans not only respect possession of resources, they also respect ownership. Ownership can be viewed as a cooperative arrangement, where individuals inhibit their tendency to take others' property on the condition that those others will do the same. We investigated to what degree great apes follow this principle, as compared to human children. We conducted two experiments, in which dyads of individuals could access the same food resources. The main test of respect for ownership was whether individuals would refrain from taking their partner's resources even when the partner could not immediately access and control them. Captive apes (N = 14 dyads) failed to respect their partner's claim on food resources and frequently monopolized the resources when given the opportunity. Human children (N = 14 dyads), tested with a similar apparatus and procedure, respected their partner's claim and made spontaneous verbal references to ownership. Such respect for the property of others highlights the uniquely cooperative nature of human ownership arrangements.

Rethinking the evolution of property and possession: A review and methodological proposition

Property is a key feature of modern human society; however, identifying the origin of this multifaceted behavior poses a formidable challenge. Here, we explore the methodologies for researching the origin of property. We discuss how an interdisciplinary approach can shed light on how our human ancestors shifted behaviorally from possessing an object to having exclusive property control over it. Possession occurs when social group members only respect an individual's claim to have exclusive access to an object when the individual has physical control over the object. Property occurs when an individual can claim exclusive access to an object, without challenge, regardless of whether the object is in their physical control or not. Researchers across different disciplines have asked what, if anything, distinguishes human property behavior from the behavior of other animals? Further, when and how did this behavior evolve in our lineage? Due to the considerable methodological challenges posed by researching this topic, few studies have been able to directly address these questions. In this review, we explore the challenges involved in defining property and possession and suggest a two-step approach to interdisciplinary definitions. Next, we evaluate four core approaches to the study of property behavior: evolutionary game theory, ethology, comparative cognition, and developmental psychology. Finally, we propose an empirical study, using an ethological approach to test the presence of property and possessive behavior in a natural setting, using our closest living relative, the chimpanzee (Pan troglodytes). Overall, we argue that this field of research is at a turning point, where the novel integration of various methods may provide an explanation to the origin of property.

Chimpanzee food preferences, associative learning, and the origins of cooking

A recent report suggested that chimpanzees demonstrate the cognitive capacities necessary to understand cooking (Warneken & Rosati, 2015). We offer alternate explanations and mechanisms that could account for the behavioral responses of those chimpanzees, without invoking the understanding of cooking as a process. We discuss broader issues surrounding the use of chimpanzees in modeling hominid behavior and understanding aspects of human evolution.

Speculations on the Evolutionary Origins of System Justification

For centuries, philosophers and social theorists have wondered why people submit voluntarily to tyrannical leaders and oppressive regimes. In this article, we speculate on the evolutionary origins of system justification, that is, the ways in which people are motivated (often nonconsciously) to defend and justify existing social, economic, and political systems. After briefly recounting the logic of system justification theory and some of the most pertinent empirical evidence, we consider parallels between the social behaviors of humans and other animals concerning the acceptance versus rejection of hierarchy and dominance. Next, we summarize research in human neuroscience suggesting that specific brain regions, such as the amygdala and the anterior cingulate cortex, may be linked to individual differences in ideological preferences concerning (in)equality and social stability as well as the successful navigation of complex, hierarchical social systems. Finally, we consider some of the implications of a system justification perspective for the study of evolutionary psychology, political behavior, and social change.

Socially transmitted diffusion of a novel behavior from subordinate chimpanzees

Chimpanzees (Pan troglodytes) demonstrate much cultural diversity in the wild, yet a majority of novel behaviors do not become group-wide traditions. Since many such novel behaviors are introduced by low-ranking individuals, a bias toward copying dominant individuals ("rank-bias") has been proposed as an explanation for their limited diffusion. Previous experimental work showed that chimpanzees (Pan troglodytes) preferentially copy dominant over low-rank models. We investigated whether low ranking individuals may nevertheless successfully seed a beneficial behavior as a tradition if there are no "competing" models. In each of four captive groups, either a single high-rank (HR, n = 2) or a low-rank (LR, n = 2) chimpanzee model was trained on one method of opening a two-action puzzle-box, before demonstrating the trained method in a group context. This was followed by 8 hr of group-wide, open-access to the puzzle-box. Successful manipulations and observers of each manipulation were recorded. Barnard's exact tests showed that individuals in the LR groups used the seeded method as their first-choice option at significantly above chance levels, whereas those in the HR groups did not. Furthermore, individuals in the LR condition used the seeded method on their first attempt significantly more often than those in the HR condition. A network-based diffusion analysis (NBDA) revealed that the best supported statistical models were those in which social transmission occurred only in groups with subordinate models. Finally, we report an innovation by a subordinate individual that built cumulatively on existing methods of opening the puzzle-box and was subsequently copied by a dominant observer. These findings illustrate that chimpanzees are motivated to copy rewarding novel behaviors that are demonstrated by subordinate individuals and that, in some cases, social transmission may be constrained by high-rank demonstrators.

Chimpanzees can point to smaller amounts of food to accumulate larger amounts but they still fail the reverse-reward contingency task

The reverse-reward contingency task presents 2 food sets to an animal, and they are required to choose the smaller of the 2 sets in order to receive the larger food set. Intriguingly, the majority of species tested on the reverse-reward task fail to learn this contingency in the absence of large trial counts, correction trials, and punishment techniques. The unique difficulty of this seemingly simple task likely reflects a failure of inhibitory control which is required to point toward a smaller and less desirable reward rather than a larger and more desirable reward. This failure by chimpanzees and other primates to pass the reverse-reward task is striking given the self-control they exhibit in a variety of other paradigms. For example, chimpanzees have consistently demonstrated a high capacity for delay of gratification in order to maximize accumulating food rewards in which foods are added item-by-item to a growing set until the subject consumes the rewards. To study the mechanisms underlying success in the accumulation task and failure in the reverse-reward task, we presented chimpanzees with several combinations of these 2 tasks to determine when chimpanzees might succeed in pointing to smaller food sets over larger food sets and how the nature of the task might determine the animals' success or failure. Across experiments, 3 chimpanzees repeatedly failed to solve the reverse-reward task, whereas they accumulated nearly all food items across all instances of the accumulation self-control task, even when they had to point to small amounts of food to accumulate larger amounts. These data indicate that constraints of these 2 related but still different tasks of behavioral inhibition are dependent upon the animals' perceptions of the choice set, their sense of control over the contents of choice sets, and the nature of the task constraints. (PsycINFO Database Record

Price Discrepancy Between Sellers and Buyers When Making Decisions for the Self and Others

In daily life, people make decisions not only for themselves but also on behalf of others. There may be differences in terms of the endowment effect when making decisions in these two situations. In Study 1, this question was investigated with an existing dataset exploring the traditional endowment effect, in which 86 students ( M age = 20.8 years, SD = 5.0) at Harvard University were asked to make a decision on selling or buying a coffee mug for themselves or for others as brokers. When making decisions for the self, the average price demanded by sellers was much higher than that offered by buyers; while making decisions for others, the price discrepancy disappeared. In Study 2, a similar study was conducted with a sample of 42 Chinese university students ( M age = 22.3 years, SD = 2.5), and a similar pattern of results was obtained. Further analysis indicated that when making decisions for others, only buyers increased their valuations, therefore mitigating the seller–buyer price discrepancy. Finally, the findings were interpreted from the perspective of Construal Level Theory.

Cognitive capacities for cooking in chimpanzees

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.

Explanations of the endowment effect: an integrative review

The endowment effect is the tendency for people who own a good to value it more than people who do not. Its economic impact is consequential. It creates market inefficiencies and irregularities in valuation such as differences between buyers and sellers, reluctance to trade, and mere ownership effects. Traditionally, the endowment effect has been attributed to loss aversion causing sellers of a good to value it more than buyers. New theories and findings--some inconsistent with loss aversion--suggest evolutionary, strategic, and more basic cognitive origins. In an integrative review, we propose that all three major instantiations of the endowment effect are attributable to exogenously and endogenously induced cognitive frames that bias which information is accessible during valuation.

The Monty Hall dilemma with pigeons: No, you choose for me

In the Monty Hall dilemma, humans are initially given a choice among three alternatives, one of which has a hidden prize. After they have chosen, but before revealing whether they have won the prize, subjects are shown that one of the remaining alternatives does not have the prize, and they are asked whether they want to stay with their original choice or switch to the remaining alternative. Switching results in obtaining the prize two thirds of the time, but even after considerable training, humans fail to consistently adopt the optimal strategy of switching. Pigeons, however, show closer-to-optimal switching performance with this task. One of the reasons that humans choose suboptimally is their mistaken assumption that with two alternatives, the probabilities of winning the prize are the same for staying and switching, and staying may be preferred because of a sense of endowment (ownership of the initial response). When we tried to produce an endowment effect in pigeons by requiring 20 pecks (rather than one peck) for the initial choice, it actually resulted in faster acquisition of the switching response. In the present research with pigeons, we examined the finding from human research that subjects are more likely to switch if they are not responsible for making the initial choice (another approach to the endowment effect). Inconsistent with the findings with humans, we found that when the initial choice was made for the pigeons, they actually showed less of a tendency to switch than did pigeons that made the initial choice themselves.

Bonobos and chimpanzees exhibit human-like framing effects

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.

The evolutionary roots of human decision making

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.

Rats exhibit reference-dependent choice behavior

Human preferences depend on whether a chosen outcome appears to be a loss or a gain compared with what had been expected, i.e., in comparison to a reference point. Because reference dependence has such a strong influence on human decision-making, it is important to uncover its origins, which will in turn help delineate the underlying mechanisms. It remains unknown whether rats use reference points in decision-making, and yet, the study of rats could help address the question of whether reference dependence is evolutionarily conserved among mammals and could provide a nonhuman animal model to investigate the neural mechanisms underlying this important cognitive process. The aim of the current study was to determine whether rats show reference-dependent choice behavior. We developed a novel paradigm by modifying the "T" maze by installing "pockets" to the left and right of the "T" stem that held reward pellets so rats would potentially develop reference values for each option prior to choice. We found that the rats were indeed sensitive to the way alternatives were presented. That is, they exhibited reference-dependent choice behavior by avoiding the choice option framed as a loss (e.g., having four reward pellets in the pocket, but receiving only one), at least under conditions with certain outcomes and clear differences between the reference and outcome quantities. Despite the small number of rats in this study, this species-level capacity suggests that reference dependence in general and loss aversion in particular may be conserved traits that evolved at or before the emergence of mammals.

Biases in preferences for sequences of outcomes in monkeys

Movies, vacations, and meals are all examples of events composed of a sequence of smaller events. How do we go from our evaluations of each scene in a movie to an evaluation of the sequence as a whole? In theory, we should simply average the values of the individual events. In practice, however, we are biased towards sequences where each element tends to be better than the previous, where the last value is large, and we overweight the best (or worst) part of the sequence. To study how general these biases are we examined monkeys' preferences for sequences of rewards in a novel reward repeat task. Monkeys were first given a sequence of rewards and then chose between repeating the sequence or receiving a standard comparator sequence. We found that, like humans, monkeys overweight events that happen later in a sequence, so much so that adding a small reward to the end of a sequence can paradoxically reduce its value. Monkeys were also biased towards sequences with large peak values (the highest value in the sequence), but only following a working memory challenge, suggesting that this preference may be driven by memory limitations. These results demonstrate the cross-species nature of biases in preferences for sequences of outcomes. In addition, monkeys' consistent preference for sequences in which large values occur later challenges the generality of discounting models of intertemporal choice in animals.

Decision making: from neuroscience to psychiatry

Adaptive behaviors increase the likelihood of survival and reproduction and improve the quality of life. However, it is often difficult to identify optimal behaviors in real life due to the complexity of the decision maker's environment and social dynamics. As a result, although many different brain areas and circuits are involved in decision making, evolutionary and learning solutions adopted by individual decision makers sometimes produce suboptimal outcomes. Although these problems are exacerbated in numerous neurological and psychiatric disorders, their underlying neurobiological causes remain incompletely understood. In this review, theoretical frameworks in economics and machine learning and their applications in recent behavioral and neurobiological studies are summarized. Examples of such applications in clinical domains are also discussed for substance abuse, Parkinson's disease, attention-deficit/hyperactivity disorder, schizophrenia, mood disorders, and autism. Findings from these studies have begun to lay the foundations necessary to improve diagnostics and treatment for various neurological and psychiatric disorders.

Artifacts and essentialism

Psychological essentialism is an intuitive folk belief positing that certain categories have a non-obvious inner "essence" that gives rise to observable features. Although this belief most commonly characterizes natural kind categories, I argue that psychological essentialism can also be extended in important ways to artifact concepts. Specifically, concepts of individual artifacts include the non-obvious feature of object history, which is evident when making judgments regarding authenticity and ownership. Classic examples include famous works of art (e.g., the Mona Lisa is authentic because of its provenance), but ordinary artifacts likewise receive value from their history (e.g., a worn and tattered blanket may have special value if it was one's childhood possession). Moreover, in some cases, object history may be thought to have causal effects on individual artifacts, much as an animal essence has causal effects. I review empirical support for these claims and consider the implications for both artifact concepts and essentialism. This perspective suggests that artifact concepts cannot be contained in a theoretical framework that focuses exclusively on similarity or even function. Furthermore, although there are significant differences between essentialism of natural kinds and essentialism of artifact individuals, the commonalities suggest that psychological essentialism may not derive from folk biology but instead may reflect more domain-general perspectives on the world.

The endowment effect can extend from self to mother: evidence from an fMRI study

People typically demand more to part with goods they own than they would be willing to pay to acquire identical goods they do not own, a phenomenon known as the endowment effect [1-3]. Recently, a large body of behavioral research has suggested that the endowment effect may actually be a type of self-referent cognitive bias resulting from ownership of an object. However, the neural underpinnings of this effect are not well understood. In the present study, we used functional magnetic resonance imaging (fMRI) to explore whether brain activity can predict the extensibility of the endowment effect to items owned by another individual with a close relationship to the subject. Subjects were asked to decide whether to buy or sell their own or their mothers' possessions at various prices. Behavioral results showed an endowment effect not only for goods owned by the subjects, but also for goods owned by the subjects' mothers, providing evidence for the extensibility of the endowment effect. Neuroimaging data showed activation in the medial prefrontal cortex (MPFC) and insula in both ownership conditions. Also, MPFC activation was positively correlated with the behavioral indifference point in the sell-for-self and sell-for-mother conditions. Furthermore, psychophysiological interaction (PPI) analysis revealed that MPFC activation was accompanied by increased functional integration with insula and striatum. Together, these findings suggest that MPFC may play an important role in the extensibility of the endowment effect.

Evolution and the expression of biases: situational value changes the endowment effect in chimpanzees

Cognitive and behavioral biases, which are widespread among humans, have recently been demonstrated in other primates, suggesting a common origin. Here we examine whether the expression of one shared bias, the endowment effect, varies as a function of context. We tested whether objects lacking inherent value elicited a stronger endowment effect (or preference for keeping the object) in a context in which the objects had immediate instrumental value for obtaining valuable resources (food). Chimpanzee subjects had opportunities to trade tools when food was not present, visible but unobtainable, and obtainable using the tools. We found that the endowment effect for these tools existed only when they were immediately useful, showing that the effect varies as a function of context-specific utility. Such context-specific variation suggests that the variation seen in some human biases may trace predictably to behaviors that evolved to maximize gains in specific circumstances.

The nonobvious basis of ownership: preschool children trace the history and value of owned objects

For adults, ownership is nonobvious: (a) determining ownership depends more on an object's history than on perceptual cues, and (b) ownership confers special value on an object ("endowment effect"). This study examined these concepts in preschoolers (2.0-4.4) and adults (n=112). Participants saw toy sets in which 1 toy was designated as the participant's and 1 as the researcher's. Toys were then scrambled and participants were asked to identify their toy and the researcher's toy. By 3years of age, participants used object history to determine ownership and identified even undesirable toys as their own. Furthermore, participants at all ages showed an endowment effect (greater liking of items designated as their own). Thus, even 2-year-olds appreciate the nonobvious basis of ownership.

Carrion crows cannot overcome impulsive choice in a quantitative exchange task

The ability to control an immediate impulse in return for a more desirable – though delayed – outcome has long been thought to be a uniquely human feature. However, studies on non-human primates revealed that some species are capable of enduring delays in order to get food of higher quality or quantity. Recently two corvid species, common raven (Corvus corax) and carrion crow (Corvus corone corone), exchanged food for a higher quality reward though seemed less capable of enduring delays when exchanging for the same food type in a higher quantity. In the present study, we specifically investigated the ability of carrion crows to overcome an impulsive choice in a quantitative exchange task. After a short delay, individuals were asked to give back an initial reward (cheese) to the human experimenter in order to receive a higher amount of the same reward (two, four, or eight pieces). We tested six captive crows – three individuals never exchanged the initial reward for a higher quantity; the other three birds did exchange though at very low rates. We performed a preference test between one or more pieces of cheese in order to address whether crow poor performance could be due to an inability to discriminate between different quantities or not attributing a higher value to the higher quantities. All birds chose the higher quantities significantly more often, indicating that they can discriminate between quantities and that higher quantities are more desirable. Taken together, these results suggest that, although crows may possess the cognitive abilities to judge quantities and to overcome an impulsive choice, they do so only in order to optimize the qualitative but not quantitative output in the exchange paradigm.

The influence of loss aversion on mountain bikers' behavioral intentions

Public involvement in management decision making has received increased attention from researchers in recent years. These studies, however, have rarely considered differences in behavior resulting from gains and losses, despite ample evidence that individuals' behavior is not the same across situations. Individuals are often more sensitive to losses than gains, which research suggests is related to ownership (real or perceived) of the item lost. We present evidence from a within-subjects quasi-experimental design to test whether mountain bikers' reported intentions differ between gain based and loss based conditions. These data were analyzed using a multi-step repeated measures analysis of variance and repeated measures analysis of covariance. The results suggest that losses are more powerful than gains in motivating public engagement in management decision making. Further, the type of action was also shown to influence behavioral intentions. Additional analyses provide support to the claim that, centrality, used as a proximate measure of ownership, moderates the contextual effects on behavioral intentions. Thus, loss aversion, moderated by ownership, is a plausible explanation of stakeholder involvement.

Why we should use animals to study economic decision making - a perspective

Despite the rich tradition in psychology and biology, animals as research subjects have never gained a similar acceptance in microeconomics research. With this article, we counter this trend of negligence and try to convey the message that animal models are an indispensible complement to the literature on human economic decision making. This perspective review departs from a description of the similarities in economic and evolutionary theories of human and animal decision making, with particular emphasis on the optimality aspect that both classes of theories have in common. In a second part, we outline that actual, empirically observed decisions often do not conform to the normative ideals of economic and ecological models, and that many of the behavioral violations found in humans can also be found in animals. In a third part, we make a case that the sense or nonsense of the behavioral violations of optimality principles in humans can best be understood from an evolutionary perspective, thus requiring animal research. Finally, we conclude with a critical discussion of the parallels and inherent differences in human and animal research.

Chimpanzees' socially maintained food preferences indicate both conservatism and conformity

Chimpanzees remain fixed on a single strategy, even if a novel, more efficient, strategy is introduced. Previous studies reporting such findings have incorporated paradigms in which chimpanzees learn one behavioural method and then are shown a new one that the chimpanzees invariably do not adopt. This study provides the first evidence that chimpanzees show such conservatism even when the new method employs the identical required behaviour as the first, but for a different reward. Groups of chimpanzees could choose to exchange one of two types of inedible tokens, with each token type being associated with a different food reward: one type was rewarded with a highly preferred food (grape) and the other type was rewarded with a less preferred food (carrot). Individuals first observed a model chimpanzee from their social group trained to choose one of the two types of tokens. In one group, this token earned a carrot, while in the other, control, group the token earned a grape. In both groups, chimpanzees conformed to the trained model's choice. This was especially striking for those gaining the pieces of carrot, the less favoured reward. This resulted in a population-level trend of food choices, even when counter to their original, individual, preferences. Moreover, the chimpanzees' food preferences did not change over time, demonstrating that these results were not due to a simple shift in preferences. We discuss social factors apparent in the interactions and suggest that, despite seeming to be inefficient, in chimpanzees, conformity may benefit them, possibly by assisting with the maintenance of group relations.

Can nonhuman primates use tokens to represent and sum quantities?

It is unclear whether nonhuman animals can use physical tokens to flexibly represent various quantities by combining token values. Previous studies showed that chimpanzees (Pan troglodytes) and a macaque (Macaca mulatta) were only partly successful in tests involving sets of different-looking food containers representing different food quantities, while some capuchin monkeys (Cebus apella) have shown greater success in tests involving sets of various concrete objects representing different food quantities. Some of the discrepancy in results between these studies may be attributed to the different methods used. In an effort to reconcile these discrepancies, we presented two primates species, chimpanzees and capuchin monkeys, with two token tasks. The critical test in each task involved summing the value of multiple tokens of different types to make accurate quantity judgments. We found that, using either method, individuals of both species learned to associate individual tokens with specific quantities, as well as successfully compare individual tokens to one another or to sets of visible food items. However, regardless of method, only a few individuals exhibited the capacity to sum multiple tokens of different types and then use those summed values to make an optimal response. This suggests that flexible combination of symbolic stimuli in quantity judgments tasks is within the abilities of chimpanzees and capuchins but does not characterize the majority of individuals. Furthermore, the results suggest the need to carefully examine specific methodological details that may promote or hinder such possible representation.

Chimpanzees and bonobos distinguish between risk and ambiguity

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.

Responses to the Assurance game in monkeys, apes, and humans using equivalent procedures

There is great interest in the evolution of economic behavior. In typical studies, species are asked to play one of a series of economic games, derived from game theory, and their responses are compared. The advantage of this approach is the relative level of consistency and control that emerges from the games themselves; however, in the typical experiment, procedures and conditions differ widely, particularly between humans and other species. Thus, in the current study, we investigated how three primate species, capuchin monkeys, chimpanzees, and humans, played the Assurance (or Stag Hunt) game using procedures that were, to the best of our ability, the same across species, particularly with respect to training and pretesting. Our goal was to determine what, if any, differences existed in the ways in which these species made decisions in this game. We hypothesized differences along phylogenetic lines, which we found. However, the species were more similar than might be expected. In particular, humans who played using "nonhuman primate-friendly" rules did not behave as is typical. Thus, we find evidence for similarity in decision-making processes across the order Primates. These results indicate that such comparative studies are possible and, moreover, that in any comparison rating species' relative abilities, extreme care must be taken in ensuring that one species does not have an advantage over the others due to methodological procedures.