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Five experiments involving invisible displacements were run on a population of semi‐free‐ranging rhesus monkeys (Macaca mulatta). The goal of these experiments was to assess, without training, the kinds of expectations individuals spontaneously set up when an object has moved out of sight. The first experiment, modeled after studies of human infants and children, involved a table with one box on the top surface and a second box lined up below on the ground. An occluder was placed in front of the table, blocking the subject's view. A piece of food was then dropped behind the occluder, above the top box. The presenter then removed the occluder, walked away, and allowed the subject to approach. Consistently, subjects searched in the incorrect bottom box. This error can be interpreted as a failure to understand solidity, containment, or some other factor. It can also be interpreted as an error guided by a gravity bias, i.e. an expectation that all falling objects fall straight down or to the lowest point. Experiments 2–5 tested these alternative hypotheses. Results show that rhesus monkeys do not have an inherent bottom box bias, are not avoiding the top box, and do recognize that in some contexts boxes can contain or hold food. Thus, for example, when the two boxes are placed on the ground, one in front of the other, and occluded, subjects search in the near box after a piece of food has been rolled behind the occluder (horizontal trajectory). This shows that rhesus can solve an invisible displacement problem that involves solid containers, where one container blocks travel to the other container. We conclude that the rhesus monkey's error in Experiment 1 is guided by an expectation that all falling objects fall straight down or, at least, to the lowest point. This expectation represents a limitation of their knowledge of physical objects and events.

Human infants have considerable understanding of why objects move and what causes them to take one trajectory over another. Here, we explore the possibility that this capacity is shared with other nonhumans and present results from preferential looking time tests with a New World monkey, the cotton‐top tamarin. Experiments examined whether individuals form different expectations about an object's potential capacity to change locations. Test objects were: 1) self‐propelled, moving, animate; 2) self‐propelled, moving, inanimate; 3) non‐self‐propelled, moving due to an external agent, inanimate; 4) non‐self‐propelled, motionless, inanimate. When category 1 objects, either a live mouse or frog, emerged from behind an occluder in a novel location, this did not affect looking time; subjects appeared to expect such changes. In contrast, when the other objects emerged in a novel location following occlusion from view, subjects looked longer than when the object emerged in the location seen prior to occlusion; such locational changes were apparently not expected. Some feature other than self‐propelled motion accounts for the tamarins' looking time responses and at least one candidate feature is whether the object is animate or inanimate.

Studies often reveal a dissociation between what infants know as revealed by action and what they know as revealed by perception. We explored whether non‐human primates exhibit a similar dissociation, focusing on what rhesus macaques know about solidity. In a series of search experiments, Hauser (2001) found that rhesus do not possess a complete understanding of solidity, searching below a solid shelf for an invisibly displaced object. In the present experiments, we explored how rhesus would perform in expectancy violation versions of the same tasks. Subjects looked longer when an apple appeared to fall through a solid shelf and when it appeared to roll through a solid barrier. These results suggest that macaques have some understanding of solidity when tested using looking paradigms even though they do not appear to use this knowledge when searching for food. We speculate that this dissociation is similar to that demonstrated in human development.

Pre‐school children expect falling objects to travel in a straight line even when there are clear physical mechanisms that deviate the object's path (Hood, 1995). The current study set out to determine whether this expectancy is limited to humans. Cotton‐top tamarins (Saguinus oedipus oedipus), a New World monkey species, were tested on Hood's (1995) experimental task where objects are dropped down a chimney connected by an opaque tube to one of three containers. Like human children, there was a significant tendency to search in the container underneath the chimney where the food was dropped on the first trial, even though aligned chimneys and containers were never connected. These search errors suggest that there may be a gravity bias that operates when both primate species fail to understand the constraints operating on object trajectories. Unlike human children however, tamarins were generally more likely to perseverate in making errors even though repeated testing and cost incentives were used.

Frontmatter -- CONTENTS -- ACKNOWLEDGMENTS -- INTRODUCTION -- Part I. Epistemology after Darwin -- Introduction -- The Principles of Psychology -- The Gay Science -- The Evolution of Self- Consciousness -- The Fixation of Belief -- Great Men, Great Thoughts, and the Environment -- The Influence of Darwinism on Philosophy -- Part II. Ethics after Darwin -- Introduction -- The Descent of Man -- The Data of Ethics -- The Challenge of Facts -- The Gospel of Wealth -- Socialism -- Mutual Aid -- Human Progress: Past and Future -- The Right to Make War -- The Call of the Wild -- Principia Ethica: Naturalistic Ethics -- Evolution and Ethics -- Part III. The Evolution of Ideas -- Introduction -- Darwinism as a Metaphysical Research Programme -- The Structure of Scientific Revolutions -- The Evolutionary Development of Natural Science -- Memes and the Exploitation of Imagination -- Three Challenges for the Survival of Memetics -- Altruism in Science: A Sociobiological Model of Cooperative Behavior among Scientists -- Why Reason Can't Be Naturalized: Evolutionary Epistemology -- Part IV. The Evolution of Rationality -- Introduction -- Kant's Doctrine of the A Priori in the Light of Contemporary Biology -- The View from Somewhere: A Critical Defense of Evolutionary Epistemology -- How the Mind Works -- Evolution, Thinking, and Rationality -- The Evolutionary Argument against Naturalism: An Initial Statement of the Argument -- Darwin's Doubt, Calvin's Calvary -- Part V. Ethics and Progress -- Introduction -- On Human Nature -- A Darwinian Left: Politics, Evolution, and Cooperation -- Darwinian Conservatism -- Moral Philosophy as Applied Science -- Four Ways of "Biologicizing" Ethics -- A Defense of Evolutionary Ethics -- Part VI. The Evolution of Altruism -- Introduction -- The Liver and the Moral Organ -- Unto Others -- Is Human Morality Innate? -- Game Theory in Evolutionary Biology -- Ethics and Intuitions -- Evolution and Ethics: The Sociobiological Approach -- The Darwinian Moral Sense and Biblical Religion -- Thomistic Natural Law and the Limits of Evolutionary Psychology -- An Evolutionary Account of Evil -- Falling Up: Evolution and Original Sin -- SOURCES AND CREDITS -- FURTHER READING -- BIBLIOGRAPHY -- INDEX