Author ORCID Identifier

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Sarah F. Brosnan

Second Advisor

Michael J. Beran

Third Advisor

Heather M. Offutt

Fourth Advisor

Eyal Aharoni


Humans and animals alike make thousands of decisions each day, and good decision-making is crucial to survive and thrive in a competitive world. Much research has focused on how to make ‘rational’ decisions based on stable and absolute preferences. In reality, however, human and animal decisions are extremely context dependent. We show and act on relative rather than absolute preferences (e.g., relative to irrelevant options, previous choices, or what others receive), and these tendencies can lead to consistently ‘irrational’ behavior. Studying the flaws in our cognitive system can help us learn how it works. This dissertation explored the extent to which we share several such decision-making biases with other primates. In a series of manual and computerized tasks, capuchin monkeys’ and rhesus macaques’ choices shifted in response to theoretically irrelevant factors like the presence of unattainable options, inferior options, or social partners; how much work they had previously invested; and how frequently different stimuli were encountered. These findings suggest that evolutionary ancient mechanisms can underlie similar biases in humans, highlighting the need to evaluate the potential function of decision-making strategies in a species’ physical and social environment. However, seemingly minor aspects of the experimental paradigms, like monkeys’ baseline preferences or whether information about the reward contingencies was signaled, affected the magnitude of these biases. Such methodological details may contribute to mixed evidence for decision-making biases in animals and need to be assessed systematically for comparative research to make valid inferences. In doing so, studying whether species other than humans make similar mistakes allows us to better understand the underlying cognitive mechanisms and the evolutionary forces that shape them.


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