Sarah F. Brosnan - US grants

Economic decision making has guided human behavior for thousands of years, but little is known about the evolution and adaptiveness of such decision making in humans. Monkeys and apes provide a good model for many human behaviors due to their close evolutionary relatedness and similar cognitive abilities. This project examines the hypothesis that nonhuman primates and humans share basic economic decision making strategies that take into account partner identity and potential rewards for cooperation and defection, as well as examining how responses to computerized interactions differ from responses to face-to-face interactions in potentially cooperative situations.
A common assumption is that economic decisions rely on verbal skills, and thus are perhaps unique to verbal organisms. However, economic decision making may be more phylogentically widespread than this assumption suggests in which case such behavior may be better understood by comparing the behavior of humans with the behavior of nonhuman primate species. This study uses a well known economic decision making game called the Assurance, or Stag Hunt game. After being paired with a partner, individuals must choose between a cooperative outcome which is beneficial to both players and a non-cooperative outcome in which the partner does not receive any reward and the player receives some reward. Both individuals are better off if they cooperate; however, if a player is concerned that the partner may not cooperate, then that player is better off 'defecting', or choosing the non-cooperative option. In some situations, participants will experience face-to-face interactions with the partner, whereas in other situations the notion of ?social distance? will be introduced by having participants play computerized versions of the game. Many cooperative interactions do not pay all participants equally, and this may have a major impact on subsequent cooperation and defection. Thus, some conditions in this study will determine how responses to economic games are altered when one player receives either more rewards for cooperating (leading to unequal payoff and motivation for their partner to defect) or more rewards for defecting (leading to motivation to defect). Human and nonhuman subjects will serve as subjects in all treatments and their behavior will be compared. These data will clarify how individuals make cooperative decisions, and how such decisions are affected by face-to-face interaction and inequity. Understanding these interactions in both nonhuman primate and humans will help to more properly place nonhuman behavior in context with human behavior and to understand the roots from which human economic decision making emerged.

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."

Decades of research in economics and social psychology shows that people respond negatively to receiving worse outcomes as compared to other individuals. These reactions impact many decisions in people's daily lives and sometimes lead them to make decisions to their detriment. More recent research indicates that other species exhibit a similar reaction to inequality, often refusing rewards that are inferior to those received by their peers. However, thus far the evolutionary mechanism(s) for and function(s) of this response remain unknown, as does the reason for the significant variation seen in how the response manifests.
The proposed research examines the factors surrounding negative reactions to inequity across non-human primate species to determine 1) the mechanism(s) causing this behavioral reaction, 2) the social and/or environmental factors affecting the reaction and 3) the evolutionary history of this reaction. Seven species of primates will be asked to make decisions about whether or not to accept rewards in a series of studies in which their outcomes vary relative to their social partners. The influence of social factors like group membership and individual factors like personality will also be investigated.
The results of this research will clarify how decision-making is affected by unequal outcomes. As a CAREER project, this work offers undergraduate and graduate students multiple opportunities to become involved with interdisciplinary research, as well as providing for the development of course materials designed to enhance undergraduate education, which will be freely distributed to the community.

Despite much research regarding how animals and humans solve social problems, few studies have utilized comparable procedures, outcomes, or measures, thus little is known about the evolution of decision-making behavior. In this project, the Principal Investigators will investigate how primates, including humans, deal with problems that arise in interactions with other group members. Understanding what outcomes are achieved, and how they vary across species, has implications for theories of the evolution of sociality and our understanding of social decision-making. The research will examine strategic decisions involving costly conflict and trust, varying the cooperativeness or competitiveness of the frame. The results will provide shed light on the evolution of human decision-making behavior.

This research will help to clarify the similarities and differences between nonhuman primates and humans with respect to social decision-making and will more properly place nonhuman behavior in context with human behavior and to understand the roots from which human economic decision making emerged. In addition to the theoretical merits, this interdisciplinary research will be integrated into summer workshops for graduate, undergraduate, and high school students at the Economic Science Institute at Chapman University and disseminated to the general public through partnerships with schools and Zoo Atlanta. It will also provide training for multiple postdoctoral fellows, graduate and undergraduate students.

When faced with a choice, humans often make decisions based on their observations of the results of similar decisions made by other people. Although in some cases such comparisons can help determine the best outcome, in other contexts, such social comparisons can lead to less than optimal, and even potentially negative, decisions or outcomes. For instance, when making decisions related to personal or family economics, people may observe others (peers, colleagues, neighbors, family, etc.), to determine what is ?normal? or ?appropriate,? potentially leading to expenditures that essentially cannot be afforded (colloquially known as ?keeping up with the Joneses?) and therefore, increase their risk of financial ruin. Similarly, observations of peers, neighbors, or colleagues may lead to comparisons that result in the making of ?risky? decisions, again with potentially negative outcomes. Understanding how and why people observe and apply the decisions made by other people to the making of their own decisions, even when such comparisons are not valid or are even actively misleading, may aid in the development of strategies that can be used to help people make good decisions and minimize the probability that they will make poor ones. Because people are faced with decision-making situations on a daily basis, this research will be important for helping people to develop strategies that will help them make good decisions that promote well-being.


In this project, the Principal Investigators will study the factors that influence decision-making when individuals rely on what others receive to determine their expected outcome, also known as a reference point. Our first research goal is to explore how these reference points influence what people expect their outcomes to be. In particular, we are interested in what happens if those expectations are violated. Additionally, we are interested in what other factors surrounding the decision may influence the degree to which these reference points are used to establish expectations. These contexts include the riskiness of the situation, the degree to which an observed outcome conforms to what is typical (e.g., is only one other person receiving that outcome, or is everyone else receiving that outcome?), and, in situations in which expectations are violated, whether there is a good rationale for why one?s own outcome might differ from what is expected. Our second research goal is to understand the evolution of these behaviors. This is important because by understanding the broader biological and psychological foundations, mechanisms, and processes, we can begin to design effective interventions to counteract sub-optimal decision-making. One way to understand the biological foundations of human decision-making behavior is to explore these questions in nonhuman species. We will use methods from experimental economics to explore 1) how risk interacts with individuals? expectations about their outcomes, 2) how the social context influences individuals? expectations, and 3) whether individuals respond differently if there is a rationale for a perceived violation of expectations. Together these questions will provide an understanding of how social comparison may drive decision-making processes that could lead to negative outcomes in certain contexts. In terms of broader impacts, we have a strong focus on providing training in the scientific method to the next generation of scientists. This includes engaging undergraduate and graduate students and postdoctoral fellows in all levels of the research involved in this proposal. We will also bring this research to K-12 students in order to generate enthusiasm for science while these students are young. Additionally, good decision-making should positively impact people of all ages, so it is a particularly relevant and important topic that should easily engage students during their formative years. We accomplish this engagement by presenting our science in area K-12 schools and through community involvement in science, such as participating in public ?science nights? at local schools and involvement in science fairs by both the PIs and our students. More broadly, people encounter daily the sorts of decisions that we are exploring, and good decision making in these situations directly impacts financial, physical, and psychological well-being.

Cognitive biases cloud effective decision-making. These irrational strategies lead to inefficiencies in everything from large-scale economic systems (such as the health-care industry) to personal choices (such as picking unhealthy snack foods). This research investigates one specific bias, the Endowment Effect (EE), in which individuals tend to ask for more to sell an item in their possession than they would pay to buy it. For instance, people demanded more money to part with a Final Four basketball ticket won in a raffle than they offered to pay for such a ticket some time earlier (e.g., $2400 to sell vs $160 to buy; Carmon & Ariely, 2000). This is true even in cases where the object has accrued no additional value, even sentimental value, since it was acquired. The EE is important because over-valuing possessions leads to less efficient transactions; people demand too much in exchange for what they currently have. For children, this bias may complicate social interactions that involve possessions, such as sharing with siblings and peers.

We will investigate the emergence and development of the EE by testing how children and adults make decisions. Our first goal is to document any differences in the EE across these age groups. Our testing procedures will produce results that are comparable to existing data on the EE in non-human primates. This means that we will understand both how the EE develops in humans and how it evolved across the primates. This combined approach will help measure the degree to which biased decision-making is a result of experience and culture. Our second goal is to investigate how different features related to possession influence the EE. In particular, we will test the importance of physical versus "legal" possession (e.g., having an object vs. being told that you will receive an object) and the degree to which the EE is determined by possession of the actual object (as compared to a photo of or symbol representing the object). Finally, our research will have two broader impacts. First, these results will address the development of decision-making biases and thus help to inform the debate about how to best minimize the impacts of faulty decision-making. Additionally, we will engage students at all levels in the scientific process, including sharing these results in academic venues as well as with parents and other members of the community.

Understanding how individuals manage or fail to coordinate their behavior in social settings where coordination is beneficial is a fundamental objective of social science. To the extent such understanding informs our ability to promote or impede coordination it is also of great practical importance for improving the performance of teams or disrupting the performance of adversaries. Recent research has investigated the underpinnings of strategic interactions in social settings between humans using simple economic games drawn from game theory as models for human decision-making. Even more recently, these methods have been used to look at strategic behavior more broadly across primate species, allowing for inter-species comparisons. Much of this work, however, in both humans and other primates, has involved only pairs of individuals, whereas in the real world such decisions take place within the rapidly changing dynamics of larger social groups. The current research project will study the decisions made by two species of non-human primates, capuchin monkeys and chimpanzees, while they are interacting in their social groups. The research will focus on how these species solve coordination problems depending on the social context and ecological conditions in which the interactions occur. The research will also examine how human subjects behave in virtual environments matched to those in which the non-human primates have been studied.

The research has two primary objectives. The first is to examine who participates and doesn't in situations where individuals can coordinate (or not) to acquire a reward, how participation varies with payoffs, and how it varies with changes in social context. Two species - chimpanzees and capuchins - are selected for this part of the study because there is evidence that both cooperate, exhibit variation in success in cooperating, and are available for study in sufficiently large social groups. The second aim is to use humans to examine the influence of ecological conditions and variation in such conditions on the manifestation of strategic behavior. Subjects will make decisions in a virtual environment with specific ecological conditions and in which benefits of cooperation or anti-cooperation can be varied. The characteristics of the virtual environment will match features of environments in which behavior of capuchins and chimpanzees has already been observed to enable interspecies comparison. This part of the study will shine light on the question of how important language is to humans' remarkable ability to come to pareto optimal solutions in social interactions

Innovation and learning are fundamental human traits, but they are thought to be costly to evolve due to the cognitive capacities necessary to support them. This research project tests hypotheses relevant to understanding the context in which social learning emerges to uncover the selective pressures driving innovation, behavioral flexibility, and a propensity to learn from others. Specifically, this project investigates how ecological and social factors influence social transmission of information in primates with differing baseline use of social learning. The project provides much-needed field-based research opportunities for underrepresented and lower-income students. The project also improves research partnerships that build capacity at minority-serving institutions, and disseminates findings broadly to academic and non-academic audiences.

The study investigates social learning among non-human primates that share many features with humans, including large brains relative to body size, extensive cooperation, innovative social conventions, and refined foraging skills. These characteristics make them excellent candidates for studying the factors that influence the emergence of innovation and social learning. This research investigates how evolutionary pressures, ecological need, and social experience influence problem-solving and social learning strategies in two closely-related species that differ in tool use and social traditions that may impact their propensity to innovate and learn from others. The project will compare a) problem solving, b) behavioral flexibility, and c) social learning strategies across these populations. This research will highlight the impacts of cognitive differences, ecological necessity, and previous experiences on individuals’ ability to solve novel problems and transmit that knowledge to others.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.