Psychology, Department of


Date of this Version



Published, as Chapter 6, in Primate Neuroethology, ed. Michael L. Platt & Asif A. Ghazanfar (New York: Oxford University Press, 2010), pp. 98–116. Copyright © 2010 Michael L. Platt & Asif A. Ghazanfar. Used by permission.


Primates constantly face decisions that influence their survival and reproduction. Continue foraging in this tree or move on to another? Expose oneself to a hidden predator by straying from the group or enjoy the safety of having other potential victims nearby? Defend one’s territory from invaders or abandon it and seek a new home? In all of these cases, primates must trade off the costs and benefits associated with uncertain and delayed decision outcomes. The outcomes of these choices influence survival and reproduction, and natural selection should favor those individuals whose choices lead to the propagation of their genes.

The vast majority of economic analyses of decision making define good or “rational” decisions as those consistent with a set of mathematical principles. Yet, this ignores the evolutionary pressures on decision making for the sake of mathematical elegance (Kacelnik, 2006; Stevens, 2008). Meanwhile, the standard psychological view of decision making seeks to empirically undermine the economic theory but cannot offer an alternative explanatory theory. Here, I emphasize an evolutionarily informed framework for studying decision making: the bounded and ecological rationality approaches (Gigerenzer et al., 1999). Though these approaches have traditionally focused on human decision making, they are just as relevant for other species, including other primates. To illustrate the relevance of bounded and ecological rationality to the study of primate decision making, I begin by introducing various visions of rationality found in the economic and psychological study of decision making. I then explore how primate studies inform three aspects of decision making: utility, uncertainty, and time. Together, these aspects will guide our understanding of the evolutionary origins of primate and human rationality.