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Tool use has been linked to intelligence; the emergence of tools in human history is thought to reflect the evolution of human intelligence. Apart from the issue of intelligence, animals using tools interest biologists because tool use is a means by which an individual can expand available resources. Exploration can lead to the fortuitous discovery of how to use an object as a tool, but it is the purposeful repetition of that sequence of actions to reach a goal that is recognized as tool use. This chapter focuses on capuchin monkeys (Cebus apella) as a vehicle to discuss tool use in nonhuman primates. After providing some background on capuchins and an overview of the forms and contexts of tool use commonly observed in this genus, the chapter reviews experimental studies focusing on the number and kind of relations among object, substrate, and actions required to use an object to achieve a goal.

This chapter examines the rationality in the feeding behaviour of capuchin monkeys and provides a cautionary perspective on the link between social learning and rationality. It argues against the attribution of PP-rational social learning to the monkeys and suggests an explanation of their foraging behaviour in terms of lower-level processes operating in ways that are biased by social contexts. It contends that the monkeys' social foraging habits are better explained in terms of individual preferences and learned aversions, associative and trial and error learning, and social biases on individual learning.

Furlong and Santos survey studies of framing and situational influences on behavior in capuchin monkeys as well as humans, but they argue that both humans and monkeys can still have some control and freedom. In his comment, Hare suggests that a comparative and evolutionary approach might illuminate the function of control and free will in both humans and other species. Miller, however, is more critical of the implications that Furlong and Santos (as well as Hare) draw from their data. In their reply, Furlong and Santos argue that their main points survive these criticisms.

This chapter describes three theoretical analyses which shed light on the question as to what was different about the behavior, morphology, or circumstances of our ancestors that allowed our technology and culture to take off in such an extraordinary manner. Here, mathematical modeling has proven extremely insightful, particularly by demonstrating that high-fidelity transmission would lead to cultural traits persisting for extremely long periods. The theoretical findings supported a verbal argument that had been made previously by psychologist Michael Tomasello at the Max Planck Institute for Evolutionary Anthropology in Leipzig. Tomasello had proposed that our species' unique capabilities for language, teaching, and efficient imitation had allowed us to transmit knowledge with a higher fidelity than observed in other animals, and that this transmission fidelity explained the existence of cumulative culture (what he termed “ratcheting”) in humans, but not in other animals. The chapter ends with an account of an experimental investigation in children, chimpanzees, and capuchin monkeys that reinforces these theoretical findings.

This chapter explores the origins of our species' drive to explain the causal world. It begins by reviewing the types of information that humans use to learn causal structures. Specifically, it focuses on two aspects of human causal learning — learning through observed dependences and learning through interventions — that have gained considerable empirical attention in the past few decades. Researchers have argued that these two learning strategies are thought to provide learners with a window into the structure of causal relationships. The chapter then explores whether non-human animals are capable of using similar kinds of information to learn causal structures. It argues that a better approach to studying animals' abilities to learn causal structures might involve incorporating experimental tasks different from the training methods historically used to study animal causal learning. It reviews a set of methods recently employed by developmental psychologists for studying children's causal understanding, which might be reasonably adapted for work with animals. It concludes by discussing recent work which attempts to use just these tasks to explore causal learning in brown capuchin monkeys (Cebus paella) and points out several areas where future work can help resolve unanswered questions regarding the purported uniqueness of human causal explanations.

This chapter examines the social reciprocity of gratitude in nonhuman primates, specifically chimpanzees and capuchin monkeys. It describes how these animals show gratitude and how gratitude could be inferred in these species. It concludes with an argument for the universality of gratitude grounded in biological systems, echoing a sentiment expressed by moralist Henry Sedgwick in 1907 that gratitude is a truly universal intuition.

This chapter considers the most counterintuitive aspects of human choices and discusses why understanding the evolutionary origins of these counterintuitive features can provide insights into how human choice really works. Recent work in social psychology suggests that real human decision making violates a number of maxims we believe our choices obey. First, we do not seem to know the preferences that guide our decision making and can fall prey to the illusion that we have made a choice even in cases where we had no freedom to make one. Second, our choices appear to shape our preferences more than we realize. Even the simple act of making one decision can alter the way we think about the options involved in that decision. Finally, we experience choice-based preference changes not just in cases of real decisions; recent work suggests that even the illusion of a choice can shape the way our future preferences work. In all these ways, the real psychological processes that constitute our choices and preferences violate many of our intuitions about how our decisions actually work. Findings with capuchin monkeys also suggest that nonhuman primate choice falls short in the same ways as human choice does.