Laboratory for Comparative Economics and Social Behavior (CEBUS Lab)
My research interests lie in the intersection of complex social behavior and cognition. More specifically, I am interested in the proximate mechanisms underlying cooperation, reciprocity, and inequity aversion, as well as the evolution of exchange and economic decisions in nonhuman primates. This includes, but is not limited to, questions of what decisions individuals make and how they make these decisions, in what ways the decisions of humans and nonhumans compare, how their social or ecological environments affect their decisions and interactions, and under what circumstances they can alter their behaviors contingent upon these inputs. I approach these questions comparatively, with an interest in how these behaviors correlate with similar (appearing) behaviors in humans, and also with an interest in combining the expertise of different disciplines as I address these issues.
I have three main lines of research, all of which are generally related to economic and social decision making. First, I am particularly interested in the evolution of responses to inequity in nonhuman primates. My research, which stemmed from an assertion by behavioral economists that inequity aversion could be a trait which supports the evolution of cooperation, was the first to demonstrate such a response in any nonhuman species. This research, done in collaboration with Frans de Waal at the Yerkes National Primate Center of Emory University, initially examined the primates’ response to distributional inequity, wherein one individual receives a lesser value food reward than a partner for the same, or more, effort. I found that capuchin monkeys and chimpanzees respond to inequitable treatment by refusing to participate in interactions that are less beneficial to them than to their counterparts. This implies that the human response to inequity is evolved and, given that these species are also highly cooperative, may support the behavioral economists’ assertion. We are currently expanding this study to test the effects of different rewards and varying levels of effort.
Further research I have just completed with capuchin monkeys, using a mutualistic cooperation task with unequal rewards, implicates the behavior of the partner as another key factor in determining whether individuals choose to cooperate to obtain rewards. In this study, capuchins were less willing to continue to cooperate with partners who consistently dominated the better rewards than with those partners who shared them. Interestingly, this was true both when rewards were unequal and in control situations in which they were the same, indicating a response that is more complex than an immediate reaction to receiving less reward. This leads to further questions about the roles of cognitive decision making and social emotions in their behavior. With this work in particular, I have been able to step outside of my field and participate in conferences and other initiatives which attempted to bridge the gaps between different disciplines studying related phenomena.
A second focus, related to this, is the evolution of prosocial behavior in human and nonhuman primates. For this, we are investigating how young children and nonhuman primates behave when they have an opportunity to assist another individual, and how their behavior changes when “selfish” objectives, such as the potential for reciprocity, are included. This research has added to a growing body of information indicating that nonhuman primates excel at both cooperation and reciprocity, but appear to be motivated by self-centered rather than other-centered concerns. The chimpanzee research is being done at the University of Texas/MD Anderson Cancer Center Science Park chimpanzee colony in Bastrop, TX, in collaboration with Joseph Henrich (UBC Vancouver), Joan Silk (UCLA), and Steven Schapiro (UTMD Anderson). We recently demonstrated that chimpanzees are indifferent towards rewarding conspecifics, even at no real cost to themselves, indicating that their psychology may differ from that of humans (as determined in experimental economic games). This result ties in nicely with my previous work on inequity, which demonstrated that while individuals were averse to inequity detrimental to themselves, they showed no behavioral change when they were the advantaged partner. Recent work expanding this to allow for low-cost altruism found similar results. We are currently expanding this study to include a more highly valued food and opportunities for reciprocity, as well as examining how the relationship of the two partners affects their responses.
Finally, we are replicating this study on young children (3-6 years of age) to determine when similar prosocial tendencies appear in human development. We are testing pairs of children who know each other (in the same classroom at their daycare or school) and do not know each other (recruited independently), children who are paired with adults rather than peers, and children who are rewarded with food versus non-food items. This will help us to understand the chimpanzee results within the context of what humans actually do in an almost identical situation, rather than what we expect humans to do based on previous research.
A final line of research explicitly examines economic interactions in nonhuman species. I have done a great deal of work on exchange and barter behavior in nonhuman primates, which indicates that, while these individuals are capable of exchange, they do not understand barter in the same ways as humans do. Although this project has continued for more than 8 years, I am still pursuing different approaches to understand how their understanding differs from our own. I think this research is particularly important at this time in the field, because as more economics research is pursued with nonhuman species, it will be vitally important to make sure that these species actually meet the basic assumptions of standard human economics models. This research is based on simple paradigms, but is essential to understanding chimpanzees’ and other species’ economic thinking.
The first part of this work, done in collaboration with Frans de Waal, examined how nonhuman primates, specifically capuchin monkeys (Cebus apella) and chimpanzees (Pan troglodytes), value commodities in an experimental exchange paradigm which was designed as a token economy. This was created to mimic the reciprocal exchanges of goods and services they might experience in the wild in, for instance, food sharing, grooming, and mating markets. Both species of nonhuman primate were easily able to associate different foods with different tokens, and behaved consistently in a barter situation. However, they did not behave as research (and experience) predicts humans would respond. Instead, they tended to focus only on the higher value tokens, returning these preferentially in every situation, indicating that they did not use the same cognitive mechanisms as humans to solve the task.
I am continuing this research in several different ways. At the UT/MD Anderson Cancer Center facility, I am working in collaboration with Mark Grady, a professor of law and economics at UCLA, to investigate how chimpanzees’ food barter behavior differs from what would be expected in humans. We are interested in what factors might have caused the evolution of these differences between humans and chimpanzees, and are focusing on possession norms versus property norms. At the Language Research Center of Georgia State University, Michael Beran and I are investigating barter involving more meaningful symbols, in this case lexigrams, which are elements of a symbolic language. These chimpanzees have been exposed to lexigrams since infancy and are competent in their usage as a means of communication with humans. We are interested in how the chimpanzees treat these tokens during barter with humans, as well as whether we can induce the chimpanzees to barter with each other. The latter is not a behavior seen in the wild, but will inform our understanding of what cognitive and behavioral skills are required to participate in functional barter.
Finally, I am interested in other economic decision-making behaviors. I recently examined irrational economic behavior in chimpanzees (in the form of the Endowment Effect) to see how this species’ responses compared to humans’ responses. This research, done in collaboration with Owen Jones, a professor of law and biology at Vanderbilt University, again uses the exchange paradigm and will help clarify the evolution of this odd bias in human behavior. This should shed light not only on psychology, but on economics and law as well.
In the future, I plan to continue this interdisciplinary approach of examining both economic paradigms and the cognitive and behavioral traits, such as inequity responses, that underpin them. I also hope to continue including an element of comparative work with other species, including humans, as I think such comparisons add a great deal to our understanding of both nonhuman primate cognition and the evolution of these behaviors.
