Here is a list of current projects being conducted at the LRC.
Click the links for more details on each of these:
Comparative Economics
Metacognition
Social Influences on Decision Making
Ecological Influences on Decision Making
Self-Control
Numerical Cognition
Prospective Cognition
Cognitive Control
Evolution of Property
Evolution of Fairness
Evolution of Cooperation
Choice Behavior and Decision Making
Behavioral Endocrinology
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Comparative Economics
A powerful approach to understanding decision-making is to utilize the methodology of experimental economics. Economic games derived from experimental economics provide opportunities to better understand how and why individuals make the decisions that they do. This approach is of particular utility to comparative researchers. One common challenge to comparative research is that studies may not be comparable due to methodological differences, minimizing the effectiveness of the comparative approach and providing little insight into the evolution of the behaviors. Utilizing an experimental economics approach allows for a standardized methodology that is comparable not only between nonhuman species, but also to humans. This allows for more profound insight into the evolution of decision-making behavior. Many of the research topics in my lab take advantage of this approach.
For instance, a current project in the CEBUS lab compares three species of nonhuman primates and humans in their response to the Assurance game, a coordination game derived from experimental economics. We are currently investigating whether these species will coordinate when given the opportunity to do so and how factors such as partner identity, equity in payoffs, and the context of the task affect their performance. This approach has not only indicated strong continuities in outcome across the primates, but also informative differences. For example, not surprisingly, humans perform better than other species when given the opportunity to talk about the game, but when methodologies are held constant, and no instruction is given or conversation is allowed, humans’ performance looks like the performance of other primates. Perhaps most powerfully, we have evidence that while humans and rhesus monkeys coordinate equally well in these games, they do so using different cognitive mechanisms. Results like these highlight the importance of a multi-pronged approach for a full understanding of cognition and behavior. We are currently expanding this line of inquiry to investigate responses in other economic games in order to learn more about the evolution of decision-making across the primates.
Selected Recent Publications:
Brosnan, S. F. (2023). A comparative perspective on the human sense of justice. Evolution and Human Behavior, 44(3), 242-249.
Brosnan, S. F., & Wilson, B. J. (2023). Comparative economics: how studying other primates helps us better understand the evolution of our own economic decision making. Philosophical Transactions of the Royal Society B, 378(1876), 20210497.
Watzek, J., Smith, M. F., & Brosnan, S. F. (2018). Comparative economics: Using experimental economic paradigms to understand primate social decision-making. Evolution of primate social cognition, 129-141.
Vale, G. L., Williams, L., Webb, S. N., Schapiro, S. J., & Brosnan, S. F. (2022). Female squirrel monkeys’ (Saimiri boliviensis) responses to inequity in a group context; testing a link between cooperation and inequity responses. Animal Behaviour, 193, 51-62.
Robinson, L. M., Martínez, M., Leverett, K. L., Rossettie, M. S., Wilson, B. J., & Brosnan, S. F. (2021). Anything for a cheerio: Brown capuchins (Sapajus [Cebus] apella) consistently coordinate in an Assurance Game for unequal payoffs. American Journal of Primatology, 83(10), e23321.
Brosnan, S. F. (2021). What behaviour in economic games tells us about the evolution of non-human species’ economic decision-making behaviour. Philosophical Transactions of the Royal Society B, 376(1819), 20190670.
Addessi, E., Beran, M. J., Bourgeois-Gironde, S., Brosnan, S. F., & Leca, J. B. (2020). Are the roots of human economic systems shared with non-human primates?. Neuroscience & Biobehavioral Reviews, 109, 1-15.
Metacognition
Here, the question is whether animals may experience some sense of knowing what they do or do not know when faced with a decision. This is a difficult thing to assess in animals given the role of verbal reports in our understanding of human metacognition. However, certain experimental procedures have provided some insight into the metacognitive skills of nonhuman animals. In these tasks, monkeys are presented with various psychophysical and memory tasks for which stimuli can be categorized objectively as more difficult or less difficult for the animals based on task performance. Animals also are given an additional response option, called the uncertainty response, that acts in various ways to remove the contingencies of the primary response to the stimulus (e.g., to remove a trial from the screen rather than force the animal to classify a quantity of dots as large or small). In many cases, the animals use that response on exactly those trials for which the primary response (e.g., “large” or “small”) is made least efficiently. This suggests that the monkeys may monitor their own knowledge states when faced with decisions about how to respond to stimuli. However, alternate explanations also remain, and we are currently working to separate associative and cognitive explanations for these patterns of results (for example, to determine whether the uncertainty response is used as a result of uncertainty that is felt by the animal, or if it is used because the animal is tracking the reinforcement history of its primary responses in the presence of different kinds of stimuli). We also are examining the extent to which the use of the uncertainty response generalizes to new tasks. This also will provide an indication of the extent to which these responses reflect metacognition. In our newest work, we are examining metacognitive illusions and the degree to which animals and humans can use metacognition to selectively “offload” the most difficult tasks when faced with multiple projects to complete.Other projects, with chimpanzees, have shown that these animals seek-information based on what they know that they know, and they also provide measures of confidence in their own memory abilities. They do this by anticipating food reward for correct responses even before any feedback is given to them. This research is supported by the National Science Foundation (BCS – 2043667, BCS – 1552405, BCS – 0956993 and BCS – 0634662), the National Institute of Child Health and Human Development (RO1-HD061455) and the European Science Foundation (as part of a Eurocore Programme entitled Consciousness in a Natural and Cultural Context).
Selected Recent Publications:
James, B. T., Parrish, A. E, Guild, A. S., Creamer, C., Kelly, V., Perdue, B. M., Kelly, A. J., & Beran, M. J. (2021). Go if you know: Preschool children’s movements reflect their metacognitive monitoring. Cognitive Development, 17, 101001. Link
Smith, T. R., Parrish, A. E., Creamer, C., Rossettie, M., & Beran, M. J. (2020). Capuchin monkeys (sometimes) go when they know: Confidence movements in Sapajus apella. Cognition, 199. 104237. 
Smith, T. R., Smith, J. D., & Beran, M. J. (2018). Not knowing what one knows: A meaningful failure of metacognition in capuchin monkeys. Animal Behavior and Cognition, 5, 55-67. Click here for the full paper.
Beran, M. J., Perdue, B. M., Church, B. A., & Smith, J. D. (2016). Capuchin monkeys (Cebus apella) modulate their use of an uncertainty response depending on risk. Journal of Experimental Psychology: Animal Learning and Cognition, 42, 32-43.
Beran, M. J., Perdue, B. M., Futch, S. E., Smith, J. D., Evans, T. A., & Parrish, A. E.(2015). Go when you know: Chimpanzees’ confidence movements reflect their responses in a computerized memory task. Cognition, 142, 236-246.
Social Influences on Decision Making
Social animals are constantly faced with decisions about how to interact with other group members. My lab studies different aspects of social decision-making, which allows us to gain a full understanding of the evolution of decision-making. These can be roughly divided into two main lines of work. The first explores how the social environment influences decision-making, in particular the ways in which the identity and behavior of the partner control how subjects respond. The second explores how factors related to the individual influence how they respond in social tasks, in particular how factors beyond basic demographic features, such as subjects’ personalities or their preferences for risk and ambiguity, influence behavior in these tasks.
Selected Recent Publications:
Talbot, C. F., Mayo, L., Stoinski, T., & Brosnan, S. F. (2015). Face discriminations by orangutans (Pongo spp.) vary as a function of familiarity. Evolutionary Psychological Science, 1, 172-182.
Pasquaretta, C., Levé, M., Claidiere, N., Van De Waal, E., Whiten, A., MacIntosh, A. J., … & Sueur, C. (2014). Social networks in primates: smart and tolerant species have more efficient networks. Scientific reports, 4(1), 7600.
Hopper, L. M., Lambeth, S. P., Schapiro, S. J., & Brosnan, S. F. (2014). Social comparison mediates chimpanzees’ responses to loss, not frustration. Animal cognition, 17, 1303-1311.
Ecological Influences on Decision Making
Historically, there has been a strong assumption in psychology that species can be roughly ranked by cognitive ability, based on some aspect of brain size (or the ratio of brain to body size), and that this is typically sufficient to explain differences in cognition across species. Recent research has shattered that assumption by demonstrating homologies in behavior across species with quite different brain morphology (e.g., corvids, cetaceans, and primates). However, most cases studies are still done among highly encephalized species known to do quite well in cognitive tasks. We, in collaboration with Redouan Bshary at the University of Neuchatel, are interested in how ecology shapes cognition such that even species with very small brains can outperform species with very large brains on decision-making tasks derived from the smaller-brained species’ ecology.
For this work, we are comparing primates with another highly cooperative species, cleaner fish, to elucidate the ecological pressures that have influenced cooperation. We have found that cleaner fish do indeed outperform several primates species, including humans, on tasks that are ecologically relevant to cleaner fish but not primates. This cannot be explained by basic cognition because, even on these tasks, the primates show equally fast reversal learning, indicating that the challenge was in acquiring the task in the first place. We are currently exploring the ways in which the task can be tweaked to increase the primates’ performance and, importantly, testing the fish on tasks derived from primate ecology.
Selected Recent Publications:
Ciacci, F., Mayerhoff, S., De Petrillo, F., Gastaldi, S., Brosnan, S. F., & Addessi, E. (2023). State‐dependent risky choices in primates: Variation in energy budget does not affect tufted capuchin monkeys’ (Sapajus spp.) risky choices. American Journal of Primatology, 85(10), e23542.
Webster, M. F., Leverett, K. L., Williamson, R., & Brosnan, S. F. (2023). Children’s endowment effect is impacted by the salience of the object, but not the duration of possession or the object’s tangibility. Cognitive Development, 66, 101331.
Wilson, B. J., Brosnan, S. F., Lonsdorf, E. V., & Sanz, C. M. (2020). Consistent differences in a virtual world model of ape societies. Scientific reports, 10(1), 14075.
Self Control
This research program focuses on the self-control behavior of nonhuman primates. Here, we use delay of gratification tasks in which animals can obtain a more preferred or larger reward by waiting to make a response whereas they obtain a smaller or lesser preferred reward if they make that response. In the most recent studies, we have used a technique in which food items accumulate as long as an animal inhibits consumption of those items. Thus, the longer the animal waits to eat the food items that are accessible, the more food items it can acquire. This rather simple technique has provided compelling evidence that chimpanzees show excellent delay of gratification (sometimes for periods in excess of 10 minutes with very highly preferred food accumulating in front of them). Even rhesus monkeys, traditionally viewed as a highly impulsive species, show some success with this task, and recent projects with a new apparatus, the rotating tray task, has shown that capuchin monkeys with very poor delay of gratification skills can improve when given that task. We also have examined the relation between attentional allocation either to the food items or to other available stimuli and delay maintenance (continued inhibition of the impulsive response). For children, attention to the reward is highly detrimental to delay maintenance, but this appears not to be true for chimpanzees. In some cases, attention to the food items may even facilitate greater delay maintenance, and so we continue to probe this relation as well as other aspects of self-control in these species. For example, we have shown that chimpanzees will use self-distraction to help aid delay of gratification, as in the photo at left where Sherman is looking through a magazine during the delay interval. This research is supported by the National Institute of Child Health and Human Development (HD-060563).
Dr. Beran wrote a book about much of his research, and that of others, called Self-Control in Animals and People. You can find it here.
Selected Publications:
Beran, M. J., & Hopkins, W. D. (2018). Self-control in chimpanzees relates to general intelligence. Current Biology, 28, 574-579.
Parrish, A. E., James, B. T., Rossettie, M. S., Smith, T. R., Otalora-Garcia, A., & Beran, M. J. (2018). Investigating the depletion effect: Self-control does not waiver in capuchin monkeys. Animal Behavior and Cognition, 118-138.
Beran, M. J., James, B. T., Whitham, W., & Parrish, A. E. (2016). Chimpanzees can point to smaller amounts of food to accumulate larger amounts but they still fail the reverse-reward contingency task. Journal of Experimental Psychology: Animal Learning and Cognition, 42, 347-358.
Beran, M. J., Perdue, B. M., Rossettie, M. S., James, B. T., Whitham, W., Walker, B., Futch, S. E., & Parrish, A. E. (2016). Self-control assessments of capuchin monkeys with the rotating tray task and the accumulation task. Behavioural Processes, 129, 68-79.
Numerical Cognition
We are interested in counting and arithmetic skills in nonhuman primates, human adults, and human children. With regard to the question of whether animals are capable of counting behavior, we have approached the question through use of computerized tests of what is called constructive enumeration.
In these tests, chimpanzees have learned to select items on a computer screen, one-at-a-time, until they have accumulated (or constructed) a set equal to a presented target numeral. Chimpanzees are successful on such tasks for numerals up to 8, but performance is indicative of a process more similar to estimation than to formal counting.
The chimpanzees show decreasing performance levels as a function of increasing set size, and they also show greater variability in the size of the constructed set as numeral values increase. This pattern indicates that the enumerative process used by the animals is approximate in its representation of set size.
We have assessed estimation skills in chimpanzees, monkeys, human adults, and human children. In these tests, participants observe as items are placed into and removed from opaque containers so that additive and subtractive operations can be presented. This sequential presentation method has produced compelling similarities in the performance of the nonhuman primates and human children. In addition, recent studies have indicated that articulatory suppression methods can block subvocal counting routines in adult humans, producing data sets that are very similar to those of nonhuman primates and children who have not yet mastered the counting routine. Thus, these comparative data strongly suggest a shared mechanism for the approximate representation of set size for sequentially presented arrays. Modifications of the testing paradigm have demonstrated that chimpanzees also are capable of responding to addition and subtraction manipulations on these arrays, and also that chimpanzees can retain numerical information resulting from enumeration processes for extended time periods (up to 20 minutes). We have examined the link between these types of numerousness judgments and the formal counting skills acquired by children. We have postulated that counting skill is not required for children to be sensitive to arithmetic manipulations as such a sensitivity appears to be widespread phylogenetically. This research is supported by the National Institute of Child Health and Human Development (HD-38051).
Selected Related Publications:
Beran, M. J., French, K., Smith, T. R., & Parrish, A. E. (2019). Limited evidence of number-space mapping in rhesus monkeys (Macaca mulatta) and capuchin monkeys (Sapajus apella). Journal of Comparative Psychology, 133, 281-293.
Beran, M. J., & Parrish, A. E. (2016). Capuchin monkeys (Cebus apella) treat small and large numbers of items similarly during a relative quantity judgment task. Psychonomic Bulletin & Review, 23, 1206-1213.
Beran, M. J., McIntyre, J. M., Garland, A., & Evans, T. A. (2013). What counts for “counting”? Chimpanzees (Pan troglodytes) respond appropriately to relevant and irrelevant information in a quantity judgment task. Animal Behaviour, 85, 987-993.
Beran, M. J., & Parrish, A. E. (2013). Visual nesting of stimuli affects rhesus monkeys’ (Macaca mulatta) quantity judgments in a bisection task. Attention, Perception, & Psychophysics, 75, 1243-1251.
Prospective Cognition
This research program focuses on the planning skills of primates and the use of prospective memory by primates including humans. People spend a lot of time thinking about the past and the future (what is sometimes called mental time travel). Being able to remember the past, including what, how, and when things happened, can be very helpful in new situations when one is not sure how to behave. Planning for the future, and remembering to carry out those plans, helps people prepare for things that are not immediately important but could be important hours, days, or even years from now. This ability to flexibly plan for the future has long been reserved for humans. In fact, it has been argued that animals are “stuck in time,” and they cannot think about the past or future because their behavior is affected only by their current needs and surroundings. If true, this would indicate a unique aspect of human memory and behavior. However, animals may show capacities for mental time travel, and such evidence would provide a better understanding of the evolutionary foundations of human memory and behavior. This project includes new tests of future-oriented thought and behavior in humans and three primate species (chimpanzees, rhesus monkeys, and capuchin monkeys). This project involves testing each species’ ability to anticipate future situations and plan future actions so as to determine continuities and discontinuities in the prospective memory and planning abilities of humans and other primates. In some cases, primates may show that they can plan for future situations that are different from present ones, and this performance will be directly compared to human performance.
Failures of prospective memory and failures to plan for the future can have profound consequences for humans. Understanding the causes of such failures is important and can benefit from a broad scientific approach that includes a comparative perspective. This project will provide a better understanding of the evolutionary emergence, as well as the limits, of planning and future-oriented thought and memory in humans and primates. These studies offer new ideas about the nature of primate memory, the beginnings of planned behavior, and the nature of prospective memory. This research will determine similarities and differences between primates and humans in their planning behavior and prospective memory and will help determine whether any of these abilities are unique to humans. The research is supported by the National Science Foundation (BCS – 0924811).
Selected Related Publications:
Kelly, A. J., Perdue, B. M., Love, M. W., Parrish, A. E., & Beran, M. J. (2018). An investigation of prospective memory with output monitoring in preschool children. American Journal of Psychology, 133, 201-210.
Beran, M. J., Parrish, A. E., Futch, S. E., Evans, T. A., & Perdue, B. M. (2015). Looking ahead? Computerized maze task performance by chimpanzees (Pan troglodytes), rhesus monkeys (Macaca mulatta), capuchin monkeys (Cebus apella), and human children (Homo sapiens). Journal of Comparative Psychology, 129, 160-173.
Beran, M. J., Perdue, B. M., & Evans, T. A. (2015). Prospective memory in nonhuman primates. Japanese Journal of Animal Psychology, 65, 23-33.
Evans, T. A., Perdue, B. M., Parrish, A. E., & Beran, M. J. (2014). The relationship between event-based prospective memory and ongoing task performance in chimpanzees (Pan troglodytes). PLoS ONE, 9, e112015. Click here for full paper.
Perdue, B. M., Beran, M. J., Williamson, R. A., Gonsiorowski, A., Evans, T. A. (2014). Prospective memory in children and chimpanzees. Animal Cognition, 17, 287-295.
Cognitive Control
Cognitive control involves a number of regulatory or executive processes that allocate attention, manipulate and evaluate available information (and, when necessary, seek additional information), plan future behaviors, and deal with distraction and impulsivity when they are threats to goal achievement. These processes are considered a feature of human cognition and an important developmental milestone. Many of the other research projects in our lab relate to cognitive control. Studies of self-control, prospective memory, and metacognition all also highlight aspects of cognitive control.
In addition, we are studying this construct using tasks in which animals and children are given conflicting cues, or distracting information, to determine the degree to which they can make smart choices.
For example, we are testing children and chimpanzees on tasks where they must remember where rewards is located, and not be distracted by labels (lexigrams or photos) on the opaque containers that cover those rewards because they are a distraction. In other tests, we are examining how post-event information that is misleading might disrupt memory, or even create false memories.
Selected Related Publications:
Beran, M. J. (2017). To err is (not only) human: Fallibility as a window into primate cognition. Comparative Cognition & Behavior Reviews, 12, 57-81.
Parrish, A. E., Otalora-Garcia, A., & Beran, M. J. (2017). Dealing with interference: Chimpanzees respond to conflicting cues in a food-choice memory task. Journal of Experimental Psychology: Animal Learning and Cognition, 43, 366-376.
Beran, M. J., Menzel, C. R., Parrish, A. E., Perdue, B. M., Sayers, K., Smith, J. D., & Washburn, J. D. (2016). Primate cognition: Attention, episodic memory, prospective memory, self-control, and metacognition as examples of cognitive control in nonhuman primates. WIREs Cognitive Science. doi: 10.1002/wcs.1397
Beran, M. J. (2015). Chimpanzee cognitive control. Current Directions in Psychological Science, 24, 352-357.
Evolution of Property
Individual property is a rarity in most species of nonhuman primates, most likely because their lifestyles are not conducive to the maintenance of property. Nonetheless, just because these species do not frequently maintain property does not mean that they lack the propensity to do so. Recent research from the CEBUS lab has shed light on primates’ concepts of property. First, we find that chimpanzees and capuchins are quite good at barter between themselves and a human experimenter, and appropriately respond based on the value of the objects. Moreover, chimpanzees will barter with conspecifics, yet ceased doing so as soon as experimenter control was removed. Property concepts beyond possession may be challenging for chimpanzees due to the risks involved when social and institutional controls for maintaining property (e.g. gossip or legal mechanisms) are lacking.
Second, we have found evidence of an endowment effect in several apes, similar to that seen in humans. These individuals prefer to maintain property that they have in their possession over trading it for something that they prefer in a free-choice context, showing that they and we share biases in common with respect to property in common. Moreover, these apes can be used as a model system to study these property biases. For instance, new research in our lab shows that chimpanzees show the endowment effect for food objects, but not for toys, and for tools that can be used to get food, but only when that food is both visible and immediately accessible. Thus, for identical items, the endowment effect is only triggered when that item is immediately useful in an evolutionarily relevant context. I have recently received a grant with psychologist Rebecca Williamson to use the non-verbal methods we developed for primates to test young children. We will explore at what age they begin to show the effect, and how properties such as physical possession (vs. property without actual possession) and symbols of property influence the perception of children that something is “theirs.” By comparing these data, we gain perspective on how human property concepts have evolved.
Selected Related Publications:
Webster, M. F., Leverett, K. L., Williamson, R., & Brosnan, S. F. (2023). Children’s endowment effect is impacted by the salience of the object, but not the duration of possession or the object’s tangibility. Cognitive Development, 66, 101331.
Brosnan, S. F., & Jones, O. D. (2023). Using an evolutionary approach to improve predictive ability in the social sciences: Property, the endowment effect, and law. Evolution and Human Behavior, 44(3), 222-228.
Jaeger, C. B., Brosnan, S. F., Levin, D. T., & Jones, O. D. (2020). Predicting variation in endowment effect magnitudes. Evolution and Human Behavior, 41(3), 253-259.
Evolution of Cooperation
Humans routinely confront situations that require coordination between individuals, from mundane activities, such as planning where to go for dinner, to incredibly complicated activities, such as international agreements or transnational ventures (such as the International Space Station). Moreover, despite some failure, we frequently succeed in these situations. How did this ability arise, and what prevents success in those situations in which it breaks down? To understand how this capability has evolved, the CEBUS lab utilizes an explicitly comparative approach at both the species and individual levels.
At the species level, we explore how individuals in many different species make these decisions, how these decisions differ across species, and what underlying mechanisms support successful cooperation. By determining how these species’ responses correlate with different aspects of the socio-ecology of each species, we can begin to make informed guesses about the function of behavior, or why it evolved. For instance, in one line of research we have discovered a correlation between species that respond negatively to inequity and the tendency to cooperate with non-kin outside of family groups. We also find that primates coordinate on economic games, but that Old World primates find better outcomes than do New World primates, indicating a split within the primate taxon.
At the individual level, we use a similar approach to explore how differences in decision-making outcomes within a species correlate with aspects of an individual’s demographic characteristics, such as age, rank, sex, or personality, as well as social variables, such as individuals’ relationships. Finally, we are exploring how hormones such as oxytocin affect decision-making in primates. Our recent evidence indicates that oxytocin actually decreases food sharing in capuchin monkeys, so our main interest is in understanding what effect these hormones are really having on behavior, and how this varies across species. Such studies help us to better understanding the evolution of cooperation in primates, and hence provide insight into how cooperation works in humans.
Selected Related Publications:
Martínez, M., Robinson, L. M., Brosnan, S. F., & Range, F. (2023). Dogs take into account the actions of a human partner in a cooperative task. Proceedings of the Royal Society B, 290(1993), 20222189.
Vale, G. L., Williams, L., Webb, S. N., Schapiro, S. J., & Brosnan, S. F. (2022). Female squirrel monkeys’(Saimiri boliviensis) responses to inequity in a group context; testing a link between cooperation and inequity responses. Animal Behaviour, 193, 51-62.
Watzek, J., Hauber, M. E., Jack, K. M., Murrell, J. R., Tecot, S. R., & Brosnan, S. F. (2021). Modelling collective decision-making: Insights into collective anti-predator behaviors from an agent-based approach. Behavioural Processes, 193, 104530.
Brosnan, S. F. (2020). Building Peace through Social Relationships. Peacebuilding Paradigms: The Impact of Theoretical Diversity on Implementing Sustainable Peace, 59.
Evolution of Fairness
Humans often respond negatively when receiving a less good outcome than another person (inequity), a behavior which is hypothesized to be a mechanism to support successful cooperation. First documented by me and Frans de Waal in capuchin monkeys, we have since found evidence that several primate species respond negatively if they receive a less good reward than a social partner for completing the same task. This requires the individuals to take into account both their own and their partners’ rewards or procedures and make assessments of their outcome based upon these parameters. We have found in particular that this response is contingent upon a task, and does not occur when rewards are provided for free. Moreover, among most primates, while effort seems to enhance the response, individuals are more sensitive to different rewards than to different levels of effort. Finally, there is variation among individuals within a species, which seems to be based upon individual differences, rather than differences in relationship quality.
While this indicates that the behavior is not unique to humans, it does not provide an evolutionary explanation for the emergence of inequity responses due to the behavioral similarities among the initial species studied, capuchin monkeys and chimpanzees. Thus, the inequity response could be due to either an evolutionary homology or a convergence based on one or more of these traits. To address this, we have recently tested several additional primate species (orangutans, squirrel monkeys, owl monkeys, rhesus monkeys, and common marmosets), which differ on these dimensions, using the same paradigm as in previous work in my lab. We find that these other species do not show responses to inequity, indicating that the response is a convergent behavior that likely emerged in the context of cooperation among non-kin not from the same family group. This response is likely a partner choice mechanism by which individuals recognize when they would do better in a new cooperative relationship.
Of course, a true sense of fairness involves two components: responding when one receives less and responding when others do. The inequity studies just described address only the first of these: how subjects respond when their partners get more than them. Recent evidence indicates that chimpanzees (and likely other cognitively advanced social species) also change their behavior when they get more than a partner, at least when their partner has some recourse. This indicates that the evolution of fairness involves two steps. In first order fairness, species evolve to respond negatively to inequity as a way for individuals to recognize the value of their cooperative partners, and therefore increase their payoffs from cooperation. In second order fairness, species evolve to recognize when they receive more than a cooperative partner, and act to ameliorate this inequity in order to maintain a beneficial cooperative relationship. Humans, with our advanced abilities at foresight and our ability to delay gratification for a long-term gain, then developed the full-blown sense of fairness that we see today.
Selected Related Publications:
Brosnan, S. F. (2023). A comparative perspective on the human sense of justice. Evolution and Human Behavior, 44(3), 242-249.
Sosnowski, M. J., Drayton, L. A., Prétôt, L., Carrigan, J., Stoinski, T. S., & Brosnan, S. F. (2021). Western lowland gorillas (Gorilla gorilla gorilla) do not show an aversion to inequity in a token exchange task. American Journal of Primatology, 83(10), e23326.
Brosnan, S. F. (2019). The biology of fairness. Social Psychology and Justice, 21-45.
Talbot, C. F., Parrish, A. E., Watzek, J., Essler, J. L., Leverett, K. L., Paukner, A., & Brosnan, S. F. (2018). The influence of reward quality and quantity and spatial proximity on the responses to inequity and contrast in capuchin monkeys (Cebus [Sapajus] apella). Journal of Comparative Psychology, 132(1), 75.
Choice Behavior and Decision Making
How do we choose? Why do we choose? To what extent are our choices affected by external factors in the environment? We ask these questions and others through studying choice in adults, children, and nonhuman animals. For example, we have studied the decoy effect, in which the presentation of a third, typically unwanted option (such as the $6.50 popcorn) changes how you might feel about the other two options compared to when it is not present. In some cases, other animals show this decoy effect as well.
We also have studied the effects of having choices on performance. For example, monkeys prefer to play computer games in which they can choose the tasks in the order they complete them compared to being given those games in the same order, but without control over choosing them. This is “choice for choice” and reflects the value that animals place on having options.
Selected Related Publications:
Parrish, A. E., Evans, T. A., & Beran, M. J. (2015). Rhesus macaques (Macaca mulatta) exhibit the decoy effect in a perceptual discrimination task. Attention, Perception, & Psychophysics, 77, 1715-1725.
Perdue, B. M., Evans, T. A., Washburn, D. A., Rumbaugh, D. M., & Beran, M. J. (2014). Do monkeys choose to choose? Learning & Behavior, 42, 164-175.
Klein, E. D., Evans, T. A., Schultz, N. B., & Beran, M. J. (2013). Learning how to “make a deal”: Human and monkey performance when repeatedly faced with the Monty Hall Dilemma. Journal of Comparative Psychology, 127, 103-108.
Behavioral Endocrinology
We are interested in the mechanisms that underpin social behavior. As part of this, we look at how endogenous hormone levels correlate with behavioral outcomes in order to understand how hormones may influence behavior. This is particularly valuable for comparative work because many hormones are highly conserved across species. Our lab is currently studying oxytocin, testosterone, and cortisol in capuchin monkeys to better understand how these correlate with different contexts. Although most of our work focuses on endogenous changes, one line of work also explores how exogenous and endogenous increases in oxytocin influence social behavior.
Selected Related Publications:
Sosnowski, M. J., Reilly, O. T., Brosnan, S. F., & Benítez, M. E. (2023). Oxytocin increases during fur‐rubbing regardless of level of social contact in tufted capuchin monkeys. American Journal of Primatology, e23490.
Sosnowski, M. J., Benítez, M. E., & Brosnan, S. F. (2022). Endogenous cortisol correlates with performance under pressure on a working memory task in capuchin monkeys. Scientific Reports, 12(1), 953.
Smith, M. F., Leverett, K. L., Wilson, B. J., & Brosnan, S. F. (2019). Capuchin monkeys (Sapajus [Cebus] apella) play Nash equilibria in dynamic games, but their decisions are likely not influenced by oxytocin. American Journal of Primatology, 81(4), e22973.
Benítez, M. E., Sosnowski, M. J., Tomeo, O. B., & Brosnan, S. F. (2018). Urinary oxytocin in capuchin monkeys: Validation and the influence of social behavior. American Journal of Primatology, 80(10), e22877.
Here, the question is whether animals may experience some sense of knowing what they do or do not know when faced with a decision. This is a difficult thing to assess in animals given the role of verbal reports in our understanding of human metacognition. However, certain experimental procedures have provided some insight into the metacognitive skills of nonhuman animals. In these tasks, monkeys are presented with various psychophysical and memory tasks for which stimuli can be categorized objectively as more difficult or less difficult for the animals based on task performance. Animals also are given an additional response option, called the uncertainty response, that acts in various ways to remove the contingencies of the primary response to the stimulus (e.g., to remove a trial from the screen rather than force the animal to classify a quantity of dots as large or small). In many cases, the animals use that response on exactly those trials for which the primary response (e.g., “large” or “small”) is made least efficiently. This suggests that the monkeys may monitor their own knowledge states when faced with decisions about how to respond to stimuli. However, alternate explanations also remain, and we are currently working to separate associative and cognitive explanations for these patterns of results (for example, to determine whether the uncertainty response is used as a result of uncertainty that is felt by the animal, or if it is used because the animal is tracking the reinforcement history of its primary responses in the presence of different kinds of stimuli). We also are examining the extent to which the use of the uncertainty response generalizes to new tasks. This also will provide an indication of the extent to which these responses reflect metacognition. In our newest work, we are examining metacognitive illusions and the degree to which animals and humans can use metacognition to selectively “offload” the most difficult tasks when faced with multiple projects to complete.Other projects, with chimpanzees, have shown that these animals seek-information based on what they know that they know, and they also provide measures of confidence in their own memory abilities. They do this by anticipating food reward for correct responses even before any feedback is given to them. This research is supported by the National Science Foundation (BCS – 2043667, BCS – 1552405, BCS – 0956993 and BCS – 0634662), the National Institute of Child Health and Human Development (RO1-HD061455) and the European Science Foundation (as part of a Eurocore Programme entitled Consciousness in a Natural and Cultural Context).
Selected Recent Publications:
James, B. T., Parrish, A. E, Guild, A. S., Creamer, C., Kelly, V., Perdue, B. M., Kelly, A. J., & Beran, M. J. (2021). Go if you know: Preschool children’s movements reflect their metacognitive monitoring. Cognitive Development, 17, 101001. Link
Smith, T. R., Parrish, A. E., Creamer, C., Rossettie, M., & Beran, M. J. (2020). Capuchin monkeys (sometimes) go when they know: Confidence movements in Sapajus apella. Cognition, 199. 104237.
Smith, T. R., Smith, J. D., & Beran, M. J. (2018). Not knowing what one knows: A meaningful failure of metacognition in capuchin monkeys. Animal Behavior and Cognition, 5, 55-67. Click here for the full paper.
Beran, M. J., Perdue, B. M., Church, B. A., & Smith, J. D. (2016). Capuchin monkeys (Cebus apella) modulate their use of an uncertainty response depending on risk. Journal of Experimental Psychology: Animal Learning and Cognition, 42, 32-43.
Beran, M. J., Perdue, B. M., Futch, S. E., Smith, J. D., Evans, T. A., & Parrish, A. E.(2015). Go when you know: Chimpanzees’ confidence movements reflect their responses in a computerized memory task. Cognition, 142, 236-246.
Social Influences on Decision Making
Social animals are constantly faced with decisions about how to interact with other group members. My lab studies different aspects of social decision-making, which allows us to gain a full understanding of the evolution of decision-making. These can be roughly divided into two main lines of work. The first explores how the social environment influences decision-making, in particular the ways in which the identity and behavior of the partner control how subjects respond. The second explores how factors related to the individual influence how they respond in social tasks, in particular how factors beyond basic demographic features, such as subjects’ personalities or their preferences for risk and ambiguity, influence behavior in these tasks.
Selected Recent Publications:
Talbot, C. F., Mayo, L., Stoinski, T., & Brosnan, S. F. (2015). Face discriminations by orangutans (Pongo spp.) vary as a function of familiarity. Evolutionary Psychological Science, 1, 172-182.
Pasquaretta, C., Levé, M., Claidiere, N., Van De Waal, E., Whiten, A., MacIntosh, A. J., … & Sueur, C. (2014). Social networks in primates: smart and tolerant species have more efficient networks. Scientific reports, 4(1), 7600.
Hopper, L. M., Lambeth, S. P., Schapiro, S. J., & Brosnan, S. F. (2014). Social comparison mediates chimpanzees’ responses to loss, not frustration. Animal cognition, 17, 1303-1311.
Ecological Influences on Decision Making
Historically, there has been a strong assumption in psychology that species can be roughly ranked by cognitive ability, based on some aspect of brain size (or the ratio of brain to body size), and that this is typically sufficient to explain differences in cognition across species. Recent research has shattered that assumption by demonstrating homologies in behavior across species with quite different brain morphology (e.g., corvids, cetaceans, and primates). However, most cases studies are still done among highly encephalized species known to do quite well in cognitive tasks. We, in collaboration with Redouan Bshary at the University of Neuchatel, are interested in how ecology shapes cognition such that even species with very small brains can outperform species with very large brains on decision-making tasks derived from the smaller-brained species’ ecology.
For this work, we are comparing primates with another highly cooperative species, cleaner fish, to elucidate the ecological pressures that have influenced cooperation. We have found that cleaner fish do indeed outperform several primates species, including humans, on tasks that are ecologically relevant to cleaner fish but not primates. This cannot be explained by basic cognition because, even on these tasks, the primates show equally fast reversal learning, indicating that the challenge was in acquiring the task in the first place. We are currently exploring the ways in which the task can be tweaked to increase the primates’ performance and, importantly, testing the fish on tasks derived from primate ecology.
Selected Recent Publications:
Ciacci, F., Mayerhoff, S., De Petrillo, F., Gastaldi, S., Brosnan, S. F., & Addessi, E. (2023). State‐dependent risky choices in primates: Variation in energy budget does not affect tufted capuchin monkeys’ (Sapajus spp.) risky choices. American Journal of Primatology, 85(10), e23542.
Webster, M. F., Leverett, K. L., Williamson, R., & Brosnan, S. F. (2023). Children’s endowment effect is impacted by the salience of the object, but not the duration of possession or the object’s tangibility. Cognitive Development, 66, 101331.
Wilson, B. J., Brosnan, S. F., Lonsdorf, E. V., & Sanz, C. M. (2020). Consistent differences in a virtual world model of ape societies. Scientific reports, 10(1), 14075.
Self Control
This research program focuses on the self-control behavior of nonhuman primates. Here, we use delay of gratification tasks in which animals can obtain a more preferred or larger reward by waiting to make a response whereas they obtain a smaller or lesser preferred reward if they make that response. In the most recent studies, we have used a technique in which food items accumulate as long as an animal inhibits consumption of those items. Thus, the longer the animal waits to eat the food items that are accessible, the more food items it can acquire. This rather simple technique has provided compelling evidence that chimpanzees show excellent delay of gratification (sometimes for periods in excess of 10 minutes with very highly preferred food accumulating in front of them). Even rhesus monkeys, traditionally viewed as a highly impulsive species, show some success with this task, and recent projects with a new apparatus, the rotating tray task, has shown that capuchin monkeys with very poor delay of gratification skills can improve when given that task. We also have examined the relation between attentional allocation either to the food items or to other available stimuli and delay maintenance (continued inhibition of the impulsive response). For children, attention to the reward is highly detrimental to delay maintenance, but this appears not to be true for chimpanzees. In some cases, attention to the food items may even facilitate greater delay maintenance, and so we continue to probe this relation as well as other aspects of self-control in these species. For example, we have shown that chimpanzees will use self-distraction to help aid delay of gratification, as in the photo at left where Sherman is looking through a magazine during the delay interval. This research is supported by the National Institute of Child Health and Human Development (HD-060563).
Dr. Beran wrote a book about much of his research, and that of others, called Self-Control in Animals and People. You can find it here.
Selected Publications:
Beran, M. J., & Hopkins, W. D. (2018). Self-control in chimpanzees relates to general intelligence. Current Biology, 28, 574-579.
Parrish, A. E., James, B. T., Rossettie, M. S., Smith, T. R., Otalora-Garcia, A., & Beran, M. J. (2018). Investigating the depletion effect: Self-control does not waiver in capuchin monkeys. Animal Behavior and Cognition, 118-138.
Beran, M. J., James, B. T., Whitham, W., & Parrish, A. E. (2016). Chimpanzees can point to smaller amounts of food to accumulate larger amounts but they still fail the reverse-reward contingency task. Journal of Experimental Psychology: Animal Learning and Cognition, 42, 347-358.
Beran, M. J., Perdue, B. M., Rossettie, M. S., James, B. T., Whitham, W., Walker, B., Futch, S. E., & Parrish, A. E. (2016). Self-control assessments of capuchin monkeys with the rotating tray task and the accumulation task. Behavioural Processes, 129, 68-79.
Numerical Cognition
We are interested in counting and arithmetic skills in nonhuman primates, human adults, and human children. With regard to the question of whether animals are capable of counting behavior, we have approached the question through use of computerized tests of what is called constructive enumeration.
In these tests, chimpanzees have learned to select items on a computer screen, one-at-a-time, until they have accumulated (or constructed) a set equal to a presented target numeral. Chimpanzees are successful on such tasks for numerals up to 8, but performance is indicative of a process more similar to estimation than to formal counting.
The chimpanzees show decreasing performance levels as a function of increasing set size, and they also show greater variability in the size of the constructed set as numeral values increase. This pattern indicates that the enumerative process used by the animals is approximate in its representation of set size.
We have assessed estimation skills in chimpanzees, monkeys, human adults, and human children. In these tests, participants observe as items are placed into and removed from opaque containers so that additive and subtractive operations can be presented. This sequential presentation method has produced compelling similarities in the performance of the nonhuman primates and human children. In addition, recent studies have indicated that articulatory suppression methods can block subvocal counting routines in adult humans, producing data sets that are very similar to those of nonhuman primates and children who have not yet mastered the counting routine. Thus, these comparative data strongly suggest a shared mechanism for the approximate representation of set size for sequentially presented arrays. Modifications of the testing paradigm have demonstrated that chimpanzees also are capable of responding to addition and subtraction manipulations on these arrays, and also that chimpanzees can retain numerical information resulting from enumeration processes for extended time periods (up to 20 minutes). We have examined the link between these types of numerousness judgments and the formal counting skills acquired by children. We have postulated that counting skill is not required for children to be sensitive to arithmetic manipulations as such a sensitivity appears to be widespread phylogenetically. This research is supported by the National Institute of Child Health and Human Development (HD-38051).
Selected Related Publications:
Beran, M. J., French, K., Smith, T. R., & Parrish, A. E. (2019). Limited evidence of number-space mapping in rhesus monkeys (Macaca mulatta) and capuchin monkeys (Sapajus apella). Journal of Comparative Psychology, 133, 281-293.
Beran, M. J., & Parrish, A. E. (2016). Capuchin monkeys (Cebus apella) treat small and large numbers of items similarly during a relative quantity judgment task. Psychonomic Bulletin & Review, 23, 1206-1213.
Beran, M. J., McIntyre, J. M., Garland, A., & Evans, T. A. (2013). What counts for “counting”? Chimpanzees (Pan troglodytes) respond appropriately to relevant and irrelevant information in a quantity judgment task. Animal Behaviour, 85, 987-993.
Beran, M. J., & Parrish, A. E. (2013). Visual nesting of stimuli affects rhesus monkeys’ (Macaca mulatta) quantity judgments in a bisection task. Attention, Perception, & Psychophysics, 75, 1243-1251.
Prospective Cognition
This research program focuses on the planning skills of primates and the use of prospective memory by primates including humans. People spend a lot of time thinking about the past and the future (what is sometimes called mental time travel). Being able to remember the past, including what, how, and when things happened, can be very helpful in new situations when one is not sure how to behave. Planning for the future, and remembering to carry out those plans, helps people prepare for things that are not immediately important but could be important hours, days, or even years from now. This ability to flexibly plan for the future has long been reserved for humans. In fact, it has been argued that animals are “stuck in time,” and they cannot think about the past or future because their behavior is affected only by their current needs and surroundings. If true, this would indicate a unique aspect of human memory and behavior. However, animals may show capacities for mental time travel, and such evidence would provide a better understanding of the evolutionary foundations of human memory and behavior. This project includes new tests of future-oriented thought and behavior in humans and three primate species (chimpanzees, rhesus monkeys, and capuchin monkeys). This project involves testing each species’ ability to anticipate future situations and plan future actions so as to determine continuities and discontinuities in the prospective memory and planning abilities of humans and other primates. In some cases, primates may show that they can plan for future situations that are different from present ones, and this performance will be directly compared to human performance.
Failures of prospective memory and failures to plan for the future can have profound consequences for humans. Understanding the causes of such failures is important and can benefit from a broad scientific approach that includes a comparative perspective. This project will provide a better understanding of the evolutionary emergence, as well as the limits, of planning and future-oriented thought and memory in humans and primates. These studies offer new ideas about the nature of primate memory, the beginnings of planned behavior, and the nature of prospective memory. This research will determine similarities and differences between primates and humans in their planning behavior and prospective memory and will help determine whether any of these abilities are unique to humans. The research is supported by the National Science Foundation (BCS – 0924811).
Selected Related Publications:
Kelly, A. J., Perdue, B. M., Love, M. W., Parrish, A. E., & Beran, M. J. (2018). An investigation of prospective memory with output monitoring in preschool children. American Journal of Psychology, 133, 201-210.
Beran, M. J., Parrish, A. E., Futch, S. E., Evans, T. A., & Perdue, B. M. (2015). Looking ahead? Computerized maze task performance by chimpanzees (Pan troglodytes), rhesus monkeys (Macaca mulatta), capuchin monkeys (Cebus apella), and human children (Homo sapiens). Journal of Comparative Psychology, 129, 160-173.
Beran, M. J., Perdue, B. M., & Evans, T. A. (2015). Prospective memory in nonhuman primates. Japanese Journal of Animal Psychology, 65, 23-33.
Evans, T. A., Perdue, B. M., Parrish, A. E., & Beran, M. J. (2014). The relationship between event-based prospective memory and ongoing task performance in chimpanzees (Pan troglodytes). PLoS ONE, 9, e112015. Click here for full paper.
Perdue, B. M., Beran, M. J., Williamson, R. A., Gonsiorowski, A., Evans, T. A. (2014). Prospective memory in children and chimpanzees. Animal Cognition, 17, 287-295.
Cognitive Control
Cognitive control involves a number of regulatory or executive processes that allocate attention, manipulate and evaluate available information (and, when necessary, seek additional information), plan future behaviors, and deal with distraction and impulsivity when they are threats to goal achievement. These processes are considered a feature of human cognition and an important developmental milestone. Many of the other research projects in our lab relate to cognitive control. Studies of self-control, prospective memory, and metacognition all also highlight aspects of cognitive control.
In addition, we are studying this construct using tasks in which animals and children are given conflicting cues, or distracting information, to determine the degree to which they can make smart choices.
For example, we are testing children and chimpanzees on tasks where they must remember where rewards is located, and not be distracted by labels (lexigrams or photos) on the opaque containers that cover those rewards because they are a distraction. In other tests, we are examining how post-event information that is misleading might disrupt memory, or even create false memories.
Selected Related Publications:
Beran, M. J. (2017). To err is (not only) human: Fallibility as a window into primate cognition. Comparative Cognition & Behavior Reviews, 12, 57-81.
Parrish, A. E., Otalora-Garcia, A., & Beran, M. J. (2017). Dealing with interference: Chimpanzees respond to conflicting cues in a food-choice memory task. Journal of Experimental Psychology: Animal Learning and Cognition, 43, 366-376.
Beran, M. J., Menzel, C. R., Parrish, A. E., Perdue, B. M., Sayers, K., Smith, J. D., & Washburn, J. D. (2016). Primate cognition: Attention, episodic memory, prospective memory, self-control, and metacognition as examples of cognitive control in nonhuman primates. WIREs Cognitive Science. doi: 10.1002/wcs.1397
Beran, M. J. (2015). Chimpanzee cognitive control. Current Directions in Psychological Science, 24, 352-357.
Evolution of Property
Individual property is a rarity in most species of nonhuman primates, most likely because their lifestyles are not conducive to the maintenance of property. Nonetheless, just because these species do not frequently maintain property does not mean that they lack the propensity to do so. Recent research from the CEBUS lab has shed light on primates’ concepts of property. First, we find that chimpanzees and capuchins are quite good at barter between themselves and a human experimenter, and appropriately respond based on the value of the objects. Moreover, chimpanzees will barter with conspecifics, yet ceased doing so as soon as experimenter control was removed. Property concepts beyond possession may be challenging for chimpanzees due to the risks involved when social and institutional controls for maintaining property (e.g. gossip or legal mechanisms) are lacking.
Second, we have found evidence of an endowment effect in several apes, similar to that seen in humans. These individuals prefer to maintain property that they have in their possession over trading it for something that they prefer in a free-choice context, showing that they and we share biases in common with respect to property in common. Moreover, these apes can be used as a model system to study these property biases. For instance, new research in our lab shows that chimpanzees show the endowment effect for food objects, but not for toys, and for tools that can be used to get food, but only when that food is both visible and immediately accessible. Thus, for identical items, the endowment effect is only triggered when that item is immediately useful in an evolutionarily relevant context. I have recently received a grant with psychologist Rebecca Williamson to use the non-verbal methods we developed for primates to test young children. We will explore at what age they begin to show the effect, and how properties such as physical possession (vs. property without actual possession) and symbols of property influence the perception of children that something is “theirs.” By comparing these data, we gain perspective on how human property concepts have evolved.
Selected Related Publications:
Webster, M. F., Leverett, K. L., Williamson, R., & Brosnan, S. F. (2023). Children’s endowment effect is impacted by the salience of the object, but not the duration of possession or the object’s tangibility. Cognitive Development, 66, 101331.
Brosnan, S. F., & Jones, O. D. (2023). Using an evolutionary approach to improve predictive ability in the social sciences: Property, the endowment effect, and law. Evolution and Human Behavior, 44(3), 222-228.
Jaeger, C. B., Brosnan, S. F., Levin, D. T., & Jones, O. D. (2020). Predicting variation in endowment effect magnitudes. Evolution and Human Behavior, 41(3), 253-259.
Evolution of Cooperation
Humans routinely confront situations that require coordination between individuals, from mundane activities, such as planning where to go for dinner, to incredibly complicated activities, such as international agreements or transnational ventures (such as the International Space Station). Moreover, despite some failure, we frequently succeed in these situations. How did this ability arise, and what prevents success in those situations in which it breaks down? To understand how this capability has evolved, the CEBUS lab utilizes an explicitly comparative approach at both the species and individual levels.
At the species level, we explore how individuals in many different species make these decisions, how these decisions differ across species, and what underlying mechanisms support successful cooperation. By determining how these species’ responses correlate with different aspects of the socio-ecology of each species, we can begin to make informed guesses about the function of behavior, or why it evolved. For instance, in one line of research we have discovered a correlation between species that respond negatively to inequity and the tendency to cooperate with non-kin outside of family groups. We also find that primates coordinate on economic games, but that Old World primates find better outcomes than do New World primates, indicating a split within the primate taxon.
At the individual level, we use a similar approach to explore how differences in decision-making outcomes within a species correlate with aspects of an individual’s demographic characteristics, such as age, rank, sex, or personality, as well as social variables, such as individuals’ relationships. Finally, we are exploring how hormones such as oxytocin affect decision-making in primates. Our recent evidence indicates that oxytocin actually decreases food sharing in capuchin monkeys, so our main interest is in understanding what effect these hormones are really having on behavior, and how this varies across species. Such studies help us to better understanding the evolution of cooperation in primates, and hence provide insight into how cooperation works in humans.
Selected Related Publications:
Martínez, M., Robinson, L. M., Brosnan, S. F., & Range, F. (2023). Dogs take into account the actions of a human partner in a cooperative task. Proceedings of the Royal Society B, 290(1993), 20222189.
Vale, G. L., Williams, L., Webb, S. N., Schapiro, S. J., & Brosnan, S. F. (2022). Female squirrel monkeys’(Saimiri boliviensis) responses to inequity in a group context; testing a link between cooperation and inequity responses. Animal Behaviour, 193, 51-62.
Watzek, J., Hauber, M. E., Jack, K. M., Murrell, J. R., Tecot, S. R., & Brosnan, S. F. (2021). Modelling collective decision-making: Insights into collective anti-predator behaviors from an agent-based approach. Behavioural Processes, 193, 104530.
Brosnan, S. F. (2020). Building Peace through Social Relationships. Peacebuilding Paradigms: The Impact of Theoretical Diversity on Implementing Sustainable Peace, 59.
Evolution of Fairness
Humans often respond negatively when receiving a less good outcome than another person (inequity), a behavior which is hypothesized to be a mechanism to support successful cooperation. First documented by me and Frans de Waal in capuchin monkeys, we have since found evidence that several primate species respond negatively if they receive a less good reward than a social partner for completing the same task. This requires the individuals to take into account both their own and their partners’ rewards or procedures and make assessments of their outcome based upon these parameters. We have found in particular that this response is contingent upon a task, and does not occur when rewards are provided for free. Moreover, among most primates, while effort seems to enhance the response, individuals are more sensitive to different rewards than to different levels of effort. Finally, there is variation among individuals within a species, which seems to be based upon individual differences, rather than differences in relationship quality.
While this indicates that the behavior is not unique to humans, it does not provide an evolutionary explanation for the emergence of inequity responses due to the behavioral similarities among the initial species studied, capuchin monkeys and chimpanzees. Thus, the inequity response could be due to either an evolutionary homology or a convergence based on one or more of these traits. To address this, we have recently tested several additional primate species (orangutans, squirrel monkeys, owl monkeys, rhesus monkeys, and common marmosets), which differ on these dimensions, using the same paradigm as in previous work in my lab. We find that these other species do not show responses to inequity, indicating that the response is a convergent behavior that likely emerged in the context of cooperation among non-kin not from the same family group. This response is likely a partner choice mechanism by which individuals recognize when they would do better in a new cooperative relationship.
Of course, a true sense of fairness involves two components: responding when one receives less and responding when others do. The inequity studies just described address only the first of these: how subjects respond when their partners get more than them. Recent evidence indicates that chimpanzees (and likely other cognitively advanced social species) also change their behavior when they get more than a partner, at least when their partner has some recourse. This indicates that the evolution of fairness involves two steps. In first order fairness, species evolve to respond negatively to inequity as a way for individuals to recognize the value of their cooperative partners, and therefore increase their payoffs from cooperation. In second order fairness, species evolve to recognize when they receive more than a cooperative partner, and act to ameliorate this inequity in order to maintain a beneficial cooperative relationship. Humans, with our advanced abilities at foresight and our ability to delay gratification for a long-term gain, then developed the full-blown sense of fairness that we see today.
Selected Related Publications:
Brosnan, S. F. (2023). A comparative perspective on the human sense of justice. Evolution and Human Behavior, 44(3), 242-249.
Sosnowski, M. J., Drayton, L. A., Prétôt, L., Carrigan, J., Stoinski, T. S., & Brosnan, S. F. (2021). Western lowland gorillas (Gorilla gorilla gorilla) do not show an aversion to inequity in a token exchange task. American Journal of Primatology, 83(10), e23326.
Brosnan, S. F. (2019). The biology of fairness. Social Psychology and Justice, 21-45.
Talbot, C. F., Parrish, A. E., Watzek, J., Essler, J. L., Leverett, K. L., Paukner, A., & Brosnan, S. F. (2018). The influence of reward quality and quantity and spatial proximity on the responses to inequity and contrast in capuchin monkeys (Cebus [Sapajus] apella). Journal of Comparative Psychology, 132(1), 75.
Choice Behavior and Decision Making
How do we choose? Why do we choose? To what extent are our choices affected by external factors in the environment? We ask these questions and others through studying choice in adults, children, and nonhuman animals. For example, we have studied the decoy effect, in which the presentation of a third, typically unwanted option (such as the $6.50 popcorn) changes how you might feel about the other two options compared to when it is not present. In some cases, other animals show this decoy effect as well.
We also have studied the effects of having choices on performance. For example, monkeys prefer to play computer games in which they can choose the tasks in the order they complete them compared to being given those games in the same order, but without control over choosing them. This is “choice for choice” and reflects the value that animals place on having options.
Selected Related Publications:
Parrish, A. E., Evans, T. A., & Beran, M. J. (2015). Rhesus macaques (Macaca mulatta) exhibit the decoy effect in a perceptual discrimination task. Attention, Perception, & Psychophysics, 77, 1715-1725.
Perdue, B. M., Evans, T. A., Washburn, D. A., Rumbaugh, D. M., & Beran, M. J. (2014). Do monkeys choose to choose? Learning & Behavior, 42, 164-175.
Klein, E. D., Evans, T. A., Schultz, N. B., & Beran, M. J. (2013). Learning how to “make a deal”: Human and monkey performance when repeatedly faced with the Monty Hall Dilemma. Journal of Comparative Psychology, 127, 103-108.
Behavioral Endocrinology
We are interested in the mechanisms that underpin social behavior. As part of this, we look at how endogenous hormone levels correlate with behavioral outcomes in order to understand how hormones may influence behavior. This is particularly valuable for comparative work because many hormones are highly conserved across species. Our lab is currently studying oxytocin, testosterone, and cortisol in capuchin monkeys to better understand how these correlate with different contexts. Although most of our work focuses on endogenous changes, one line of work also explores how exogenous and endogenous increases in oxytocin influence social behavior.
Selected Related Publications:
Sosnowski, M. J., Reilly, O. T., Brosnan, S. F., & Benítez, M. E. (2023). Oxytocin increases during fur‐rubbing regardless of level of social contact in tufted capuchin monkeys. American Journal of Primatology, e23490.
Sosnowski, M. J., Benítez, M. E., & Brosnan, S. F. (2022). Endogenous cortisol correlates with performance under pressure on a working memory task in capuchin monkeys. Scientific Reports, 12(1), 953.
Smith, M. F., Leverett, K. L., Wilson, B. J., & Brosnan, S. F. (2019). Capuchin monkeys (Sapajus [Cebus] apella) play Nash equilibria in dynamic games, but their decisions are likely not influenced by oxytocin. American Journal of Primatology, 81(4), e22973.
Benítez, M. E., Sosnowski, M. J., Tomeo, O. B., & Brosnan, S. F. (2018). Urinary oxytocin in capuchin monkeys: Validation and the influence of social behavior. American Journal of Primatology, 80(10), e22877.
How do we choose? Why do we choose? To what extent are our choices affected by external factors in the environment? We ask these questions and others through studying choice in adults, children, and nonhuman animals. For example, we have studied the decoy effect, in which the presentation of a third, typically unwanted option (such as the $6.50 popcorn) changes how you might feel about the other two options compared to when it is not present. In some cases, other animals show this decoy effect as well.
We also have studied the effects of having choices on performance. For example, monkeys prefer to play computer games in which they can choose the tasks in the order they complete them compared to being given those games in the same order, but without control over choosing them. This is “choice for choice” and reflects the value that animals place on having options.
Selected Related Publications:
Parrish, A. E., Evans, T. A., & Beran, M. J. (2015). Rhesus macaques (Macaca mulatta) exhibit the decoy effect in a perceptual discrimination task. Attention, Perception, & Psychophysics, 77, 1715-1725.
Perdue, B. M., Evans, T. A., Washburn, D. A., Rumbaugh, D. M., & Beran, M. J. (2014). Do monkeys choose to choose? Learning & Behavior, 42, 164-175.
Klein, E. D., Evans, T. A., Schultz, N. B., & Beran, M. J. (2013). Learning how to “make a deal”: Human and monkey performance when repeatedly faced with the Monty Hall Dilemma. Journal of Comparative Psychology, 127, 103-108.
Behavioral Endocrinology
We are interested in the mechanisms that underpin social behavior. As part of this, we look at how endogenous hormone levels correlate with behavioral outcomes in order to understand how hormones may influence behavior. This is particularly valuable for comparative work because many hormones are highly conserved across species. Our lab is currently studying oxytocin, testosterone, and cortisol in capuchin monkeys to better understand how these correlate with different contexts. Although most of our work focuses on endogenous changes, one line of work also explores how exogenous and endogenous increases in oxytocin influence social behavior.
Selected Related Publications:
Sosnowski, M. J., Reilly, O. T., Brosnan, S. F., & Benítez, M. E. (2023). Oxytocin increases during fur‐rubbing regardless of level of social contact in tufted capuchin monkeys. American Journal of Primatology, e23490.
Sosnowski, M. J., Benítez, M. E., & Brosnan, S. F. (2022). Endogenous cortisol correlates with performance under pressure on a working memory task in capuchin monkeys. Scientific Reports, 12(1), 953.
Smith, M. F., Leverett, K. L., Wilson, B. J., & Brosnan, S. F. (2019). Capuchin monkeys (Sapajus [Cebus] apella) play Nash equilibria in dynamic games, but their decisions are likely not influenced by oxytocin. American Journal of Primatology, 81(4), e22973.
Benítez, M. E., Sosnowski, M. J., Tomeo, O. B., & Brosnan, S. F. (2018). Urinary oxytocin in capuchin monkeys: Validation and the influence of social behavior. American Journal of Primatology, 80(10), e22877.