Sarah Frances Brosnan

• PhD
• Professor at Georgia State University

Delayed matching-to-sample (DMTS) tasks are commonly used in the field of comparative cognition to study memory, including working memory. However, specific task demands vary across studies and species, and as such, DMTS tasks may engage different memory systems when features such as the available stimulus pool differ. Further, individual or specie...

Big team science has the potential to reshape comparative cognition research, but its implementation — especially in making fair comparisons between species, handling multisite variation and reaching researcher consensus — poses daunting challenges. Here, we propose solutions and discuss how big team science can transform the field.

The world lost a towering figure when primatologist Frans de Waal passed away on March 14, 2024. Many are aware of his multitude of contributions to the field. His ability to see what animals were actually doing changed how we viewed first primates, then other species. He shared these insights through both traditional scientific outputs, such as jo...

Big Team Science (BTS) offers immense potential for comparative cognition research, enabling larger and more diverse sample sizes, promoting open science practices, and fostering global collaboration. However, implementing BTS in comparative cognition also presents unique challenges, such as making comparisons “species fair,” dealing with multi-sit...

The ability to quickly perceive and interpret threatening facial expressions from others is critical for successfully maintaining group cohesion in social nonhuman primate species. Rapid detection of threatening or negative stimuli in the environment compared to neutral stimuli, referred to as an attentional bias toward threat, is adaptive in that...

The ability to quickly perceive others' rank minimizes costs by helping individuals behave appropriately when interacting with strangers. Indeed, humans and at least some other species can quickly determine strangers' rank or dominance based only on physical features without observing others' interactions or behavior. Nonhuman primates can determin...

Human cooperation can be facilitated by the ability to create a mental representation of one’s own actions, as well as the actions of a partner, known as action co-representation. Even though other species also cooperate extensively, it is still unclear whether they have similar capacities. The Joint Simon task is a two-player task developed to inv...

How does ecological complexity influence decision making? To facilitate interpretation, laboratory studies often focus on decision tasks with limited options, but animals presumably face more variety in the wild. For example, sometimes species must choose between ephemeral and permanent options, as with choosing between mobile prey and stationary f...

Social norms – rules governing which behaviours are deemed appropriate or inappropriate within a given community – are typically taken to be uniquely human. Recently, this position has been challenged by a number of philosophers, cognitive scientists, and ethologists, who have suggested that social norms may also be found in certain non-human anima...

Reciprocally patterned behavior is widespread in animals in the wild, but experimental evidence has been frustratingly inconsistent. Contrary to earlier contentions that this inconsistency is because reciprocity in non‐human species is a rare or fragile effect, recent authors have argued that the evidence suggests that reciprocity is widespread, th...

Many animals, including humans, must make decisions when outcomes involve risk and/or ambiguity. To explore the evolutionary roots of decision making when outcomes are unknown, we modified the Balloon Analogue Risk Task (BART) for use with tufted capuchin monkeys (Sapajus [Cebus] apella), creating the Primate Analogue Risk Task (PART). Using both t...

Studies on coordination often present animals with the choice of either cooperating or remaining inactive; however, in nature, animals may also choose to act alone. This can be modeled with the Assurance game, an economic game that has recently been used to explore decision-making in primates. We investigated whether dyads of pet dogs coordinate in...

Nonhuman primates exhibit sexual dimorphism in behavior, suggesting that there could be underlying differences in brain organization and function. Understanding this neuroanatomical variation is critical for enhancing our understanding of the evolution of sex differences in the human brain. Tufted capuchin monkeys (Sapajus [Cebus] apella) represent...

Observed behavior can be the result of complex cognitive processes that are influenced by environmental factors, physiological process, and situational features. Pressure, a feature of a situation in which an individual’s outcome is impacted by his or her own ability to perform, has been traditionally treated as a human-specific phenomenon and only...

Social interactions induce oxytocin release in many social species, suggesting that oxytocin is a critical part of social bonding among individuals. However, oxytocin also increases as a result of physical contact and stimulation, making it unclear which features of affiliative behaviors (for instance, social interaction or physical contact with a...

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 met...

Humans stand out for their capacity to flexibly cooperate, possibly because they understand their partners' role. Researchers have explored if such understanding is unique to humans by assessing whether non-human species wait to manipulate a cooperative apparatus until a delayed partner arrives. If animals do wait, then it is assumed that they reco...

Addressing the welfare needs of nonhuman primates in captivity is a significant challenge due to the differences among different species, sexes, ages, dominance groups, and individuals. Interventions that increase species typical behaviors and/or reduce atypical behaviors or stress for one species, group, individual, or context may cause the opposi...

Primates of several species respond negatively to receiving less preferred rewards than a partner for completing the same task (inequity responses), either rejecting rewards or refusing to participate in the task when disadvantaged. This has been linked to cooperation, with species that cooperate frequently refusing to participate in inequity tasks...

Thinking about possibilities plays a critical role in the choices humans make throughout their lives. Despite this, the influence of individuals' ability to consider what is possible on culture has been largely overlooked. We propose that the ability to reason about future possibilities or prospective cognition, has consequences for cultural change...

Visual attention to facial features is an important way that group-living primate species gain knowledge about others. However, where this attention is focused on the face is influenced by contextual and social features, and emerging evidence in Pan species suggests that oxytocin, a hormone involved in forming and maintaining affiliative bonds amon...

The platyrrhine family Cebidae (capuchin and squirrel monkeys) exhibit among the largest primate encephalization quotients. Each cebid lineage is also characterized by notable lineage-specific traits, with capuchins showing striking similarities to Hominidae such as high sensorimotor intelligence with tool use, advanced cognitive abilities, and beh...

Non-invasive health monitoring is advantageous for wild and captive primate populations because it reduces the need for traditional invasive techniques (i.e., anesthetization) that can be stressful and potentially harmful for individuals. The biomarker neopterin is an emerging tool in primatology to measure immune activation and immunosenescence, h...

Judges are typically tasked to consider sentencing benefits but not costs. Previous research finds that both laypeople and prosecutors discount the costs of incarceration when forming sentencing attitudes, raising important questions about whether professional judges show the same bias during sentencing. To test this, we used a vignette-based exper...

Humans often experience striking performance deficits when their outcomes are determined by their own performance, colloquially referred to as “choking under pressure.” Physiological stress responses that have been linked to both choking and thriving are well-conserved in primates, but it is unknown whether other primates experience similar effects...

Prosecutors can influence judges’ sentencing decisions by the sentencing recommendations they make—but prosecutors are insulated from the costs of those sentences, which critics have described as a correctional “free lunch.” In a nationally distributed survey experiment, we show that when a sample of (n=178) professional prosecutors were insulated...

Collective decision-making is a widespread phenomenon across organisms. Studying how animal societies make group decisions to the mutual benefit of group members, while avoiding exploitation by cheaters, can provide unique insights into the underlying cognitive mechanisms. As a step toward dissecting the proximate mechanisms that underpin collectiv...

Although individuals in some species refuse foods they normally accept if their partner receives a more preferred one, this is not true across all species. The cooperation hypothesis proposes that this species-level variability evolved because inequity aversion is a mechanism to identify situations in which cooperation is not paying off, and that s...

Unequal outcomes disrupt cooperation in some situations, but this has not been tested in the context of coordination in economic games. To explore this, we tested brown capuchins (Sapajus [Cebus] apella) on a manual version of the Stag Hunt (or Assurance) Game, in which individuals sequentially chose between two options, Stag or Hare, and were rewa...

Cumulative cultural evolution (CCE), the improvement of cultural traits over generations via social transmission, is widely believed to be unique to humans. The capacity to build upon others’ knowledge, technologies, and skills has produced the most diverse and sophisticated technological repertoire in the animal kingdom. Yet, inconsistency in both...

Large-scale studies of individual differences in innovative behavior among nonhuman animals are rare because of logistical difficulties associated with obtaining observational data on a large number of innovative individuals across multiple locations. Here, we take a different approach, using observer ratings to study individual differences in inno...

Cooperation plays a fundamental role in the success of our species. Although other species also cooperate, they do not reach the same degree of complexity or achieve the same levels of coordinated action as humans do. Why cooperation evolved to varying extents in different species remains one of the big questions for science. One way in which we ca...

Human decision-making is often swayed by irrecoverable investments even though it should only be based on future—and not past—costs and benefits. Although this sunk cost effect is widely documented and can lead to devastating losses, the underlying psychological mechanisms are unclear. To tease apart possible explanations through a comparative appr...

Procedural memory allows animals to solve previously encountered tasks over weeks, months, or years efficiently. Although thoroughly documented in vertebrate clades such as mammals and birds, studies of procedural memory in squamate reptiles are lacking. Filling the gap in knowledge regarding procedural memory in squamates is important to understan...

A goal of the comparative approach is to test a variety of species on the same task. Here, we examined whether the factors that helped capuchin monkeys improve their performance in a dichotomous choice task would generalize to three other primate species: orangutans, gorillas, and drill monkeys. In this task, subjects have access to two options, ea...

Recently, there has been great interest in the evolution of human decision-making behavior. Strategies evidenced by non-human primates in dynamic economic games can shed light on the human behavior. Experimental game theory is particularly amenable to studying this question. Comparative studies of common two-player games, including the Assurance Ga...

Practical and ethical constraints limit our ability to experimentally test socioecological theory in wild primates. We took an alternate approach to model this, allowing groups of humans to interact in a virtual world in which they had to find food and interact with both ingroup and outgroup avatars to earn rewards. We altered ratios and distributi...

Do people punish more than they would if the decision costs were more transparent? In two Internet-based vignette experiments, we tested whether juvenile sentencing recommendations among U.S. adults are responsive to variation in the salience of the taxpayer costs and public safety benefits of incarceration. Using a 2 Cost (present vs. absent) x 2...

Human decision-making is often swayed by irrecoverable investments even though it should only be based on future – and not past – costs and benefits. Although this sunk cost effect is widely documented and can lead to devastating losses, the underlying psychological mechanisms are unclear. To tease apart possible explanations through a comparative...

Theories of optimal decision-making typically assume that animals have consistent preferences among options. In reality, economic behaviour in humans and foraging behaviour in some animals is often susceptible to choice-irrelevant factors such as inferior options or conspecifics’ outcomes, but the evidence for primate decision-making is mixed. Unli...

Humans make thousands of decisions every day, and in some situations, we make reliably bad ones. Much research has explored the circumstances in which such irrational decision-making occurs, but the underlying mechanisms are often unclear. One approach that has recently gained traction is to study other species’ responses to similar scenarios to be...

Hundreds of studies demonstrate human cognitive biases that are both inconsistent with “rational” decision-making and puzzlingly patterned. One such bias, the “endowment effect” (also known as “reluctance to trade”), occurs when people instantly value an item they have just acquired at a much higher price than the maximum they would have paid to ac...

We review and analyze evidence for an evolutionary rooting of human economic behaviors and organization in non-human primates. Rather than focusing on the direct application of economic models that a priori account for animal decision behavior, we adopt an inductive definition of economic behavior in terms of the contribution of individual cognitiv...

We review and analyze evidence for an evolutionary rooting of human economic behaviors and organization in non-human primates. Rather than focusing on the direct application of economic models that a priori account for animal decision behavior, we adopt an inductive definition of economic behavior in terms of the contribution of individual cognitiv...

A core aspect of human behavior is that people evaluate themselves in comparison to others in their social group. These social comparisons impact how people see themselves, the decisions they make, and the way they behave on a daily basis. Why, however, are people so focused on relative outcomes, rather than looking at their absolute gains? The ans...

A central premise of the science of comparative affect is that we can best learn about the causes and consequences of affect by comparing affective phenomena across a variety of species, including humans. We take as a given that affect is widely shared across animals, but a key challenge is to accurately represent each species' affective experience...

Purpose At what cost to society are we willing to punish criminal offenders, and how does our awareness of those costs impact our support for punitive measures? In a nationally distributed sample of 191 Internet users, we examined the elasticity of punishment in response to information about the direct material cost of incarceration. Methods Using...

A key feature that seems to separate humans and other species is humans’ ability to conceive of death. Although other species also respond differently to deceased individuals in their groups, we do not yet know what they understand about what has happened or at what point, if ever, they understand that another individual is gone permanently. Moreov...

Learned rules help us accurately solve many problems, but by blindly following a strategy, we sometimes fail to find more efficient alternatives. Previous research found that humans are more susceptible to this "cognitive set" bias than other primates in a nonverbal computer task. We modified the task to test one hypothesis for this difference, tha...

Humans make countless choices every day that affect their health, safety, and finances. Despite the high stakes, decision-making is often irrational from the viewpoint of traditional economics, i.e., the choices made are contrary to existing preferences. This leads to negative consequences for individuals and to inefficiencies in the exchange of go...

Serotonin is a neurotransmitter that plays an important role in regulating behavior and personality in humans and other mammals. Polymorphisms in genes coding for the serotonin receptor subtype 1A (HTR1A), the serotonin transporter (SLC6A4), and the serotonin degrading enzyme monoamine oxidase A (MAOA) are associated with anxiety, impulsivity, and...

Comparative approaches to experimental economics have shed light on the evolution of social decision‐making across a range of primate species, including humans. Here we replicate our previous work looking at six pairs of capuchin monkeys' (Sapajus [Cebus] apella) responses to scenarios requiring both coordination (Assurance Game) and anti‐coordinat...

Games derived from experimental economics can be used to directly compare decision-making behavior across primate species, including humans. For example, the use of coordination games, such as the Assurance game, has shown that a variety of primate species can coordinate; however, the mechanism by which they do so appears to differ across species....

Games from experimental economics have provided insights into the evolutionary roots of social decision making in primates and other species. Multiple primate species' abilities to cooperate, coordinate and anti-coordinate have been tested utilizing variants of these simple games. Past research, however, has focused on species known to cooperate an...

Change blindness is a phenomenon in which individuals fail to detect seemingly obvious changes in their visual fields. Like humans, several animal species have also been shown to exhibit change blindness; however, no species of New World monkey has been tested to date. Nine capuchins (Sapajus [Cebus] apella) were trained to select whether or not a...

The Monty Hall Dilemma (MHD) is a simple probability puzzle famous for its counterintuitive solution. Participants initially choose among three doors, one of which conceals a prize. A different door is opened and shown not to contain the prize. Participants are then asked whether they would like to stay with their original choice or switch to the o...

This study investigated the effect of cost–benefit salience on simulated criminal punishment judgments. In two vignette‐based survey experiments, we sought to identify how the salience of decision costs influences laypeople's punishment judgments. In both experiments (N1 = 109; N2 = 398), undergraduate participants made sentencing judgments with an...

The capacity for planning in nonhuman species has long been an interest of many comparative and cognitive psychologists. There is now considerable evidence that at least great apes show both motor planning and planning for future needs in various contexts and modalities. Few studies, however, have investigated planning ability in a monkey species,...

One of the goals of studying primate social cognition is to better understand how decision-making is similar or different across primate species, including humans. Recently, researchers have begun to use paradigms from experimental economics that allow for direct comparisons across species using identical or highly similar experimental approaches....

An influential evolutionary model proposed that social anxiety biases people to treat social interactions as competitive struggles with the primary goal of avoiding status loss. Among subordinate nonhuman primates in highly hierarchical social groups, this goal leads to adaptive submissive behavior; for humans, however, affiliative responses may be...

Human and animal decision-making is known to violate rational expectations in a variety of contexts. Previous models suggest that statistical structures of real-world environments can favor such seemingly irrational behavior , but this has not been tested empirically. We tested 16 capuchin monkeys, seven rhesus monkeys, and 30 humans in a computeri...

People routinely make bad decisions. Far from being random, however, these bad decisions are often predictable, occurring reliably in specific contexts (1–3). One set of such suboptimal decisions are cognitive biases, wherein individuals make decisions that predictably violate rationality or their own best interests without a logical reason for doi...

Many species face the problems of how, when and with whom to cooperate. Comparing responses across species can reveal the evolutionary trajectory of these decisions, including in humans. Using nearly identical economic game methods to compare species could identify the evolutionary constraints and catalysts to cooperation.

In highly social species, like primates, oxytocin plays an important role in cooperation, and in the formation and maintenance of social relationships. Despite recent interest in the relationship between oxytocin and social behavior in nonhuman primates, relatively little is known about endogenous oxytocin in social New World Monkeys. In this paper...

Comparative research has taught us much about the evolution and development of human and animal behavior. Humans share not just physical and biological similarities with other species, but also many behavioral traits and, in some of these cases, the psychological mechanisms behind them. Comparing behavior and cognition across multiple species can h...

The ability to inhibit previously employed strategies and flexibly adjust behavioural responses to external conditions may be critical for individual survival. However, it is unclear which factors predict their distribution across species. Here, we investigated social inhibition and behavioural flexibility in six primate species (chimpanzees, bonob...

Numerous studies have investigated the extent to which nonhuman primates understand the goals of a partner. One limitation common to many of these studies, however, has been that animals are often required to interpret actions of heterospecifics, typically human experimenters. In this study, we tested capuchin monkeys’ understanding of goal-directe...

Recent evidence within the field of comparative psychology has demonstrated that small differences in procedure may lead to significant differences in outcome. Therefore, failing to fully explore the impact of different contexts on a behavior limits our ability to fully understand that behavior. A behavior that has exhibited substantial variation,...

How special are humans? This question drives scholarly output across both the sciences and the humanities. Whereas some disciplines, and the humanities in particular, aim at gaining a better understanding of humans per se, most biologists ultimately aim to understand life in general. This raises the question of whether and when humans are acceptabl...

One challenge of studying cognition and behavior in other species is designing studies that are intuitive and motivating to the subjects; studies that lack these features may result in false negatives and other outcomes that bias our understanding of animals’ abilities and choices. Here, Schmelz, Grueneisen, Kabalak, Jost, and Tomasello (PNAS, 114(...

Although it is well known that risk impacts decision-making, less work has looked at the role of context. For example, people gamble more in social situations, but do their preferences change when another individual may win the outcome that they lose? We hypothesized that individuals would prefer options with relatively equal payoffs when another i...

Social relationships constitute a highly rewarding context for most people, providing a source of support and nurturance, as well as protection against loneliness, depression, and even death (Cacioppo, Hawkley, & Thisted, 2010; Cohen, 2004; Steptoe, Shankar, Demakakos, & Wardle, 2013). Interpersonal relationships can also, however, be stressful. Th...

To better understand the evolutionary history of human decision-making, we compare human behavior to that of two monkey species in a symmetric game of conflict with two asymmetric equilibria. While all of these species routinely make decisions in the context of social cooperation and competition, they have different socio-ecologies, which leads to...

Reciprocal altruism provides one evolutionary explanation for cooperation, and extensive research has been conducted to discern when reciprocity occurs and the underlying proximate mechanisms. de Waal and colleagues have proposed three levels of reciprocity. Symmetry-based reciprocity is noncontingent and based on symmetries in existing relationshi...

Frans de Waal is a Dutch-born primatologist whose observational and experimental research on nonhuman primates has demonstrated the cognitive and emotional continuity between humans and other primates. His areas of influence include conflict resolution, social strategizing, reconciliation and consolation, cooperation, inequity responses, culture, a...

Animal welfare questionnaire designed by myself and Dr. Matt Leach , which we have used in different animal welfare projects.

Although growing neural evidence suggests that human and nonhuman primates share a similar face-processing mechanism, evidence from behavioural research has been mixed. If primates share a similar face-processing system, one would expect to observe similar behavioural effects in both human and nonhuman primates. A particularly robust effect observe...

Though competition and cooperation are often considered opposing forces in an arms race driving natural selection, many animals, including humans, cooperate in order to mitigate competition with others. Understanding others' psychological states, such as seeing and knowing, others' goals and intentions, and coordinating actions are all important fo...

Species vary in the ease with which they can solve apparently similar problems. This can be due to a variety of features. For instance, the ecological context of a problem will be interpreted differently by different species. This could relate to how they interpret the problem, but also, more basically, to which cue they see as key. Differences in...

One way to gain insights into personality evolution is by comparing the personality structures of related species. We compared the personality structure of 240 wild white-faced capuchin monkeys to the personality structure of 100 captive brown capuchin monkeys. An ancillary goal was to test the degree to which different personality questionnaires y...

Welfare questionnaires, which allow people who are familiar with individual animals to rate the welfare of the animals, are an underutilised tool. We designed a 12-item welfare questionnaire and tested its reliability and associations with subjective well-being (SWB), locomotor stereotypy, and personality traits. The welfare questionnaire included...