Volume 80, No. 4 December 2005 395 The Quarterly Review of Biology, December 2005, Vol. 80, No. 4 Copyright  2005 by The University of Chicago. All rights reserved. 0033-5770/2005/8004-0001$15.00 The Quarterly Review of Biology THE EVOLUTION AND FUNCTIONS OF LAUGHTER AND HUMOR: A SYNTHETIC APPROACH Matthew Gervais Programs of Psychobiology and Evolutionary Studies, Binghamton University Binghamton, New York 13902 USA e-mail: mgervai1@binghamton.edu David Sloan Wilson Departments of Biology and Anthropology, Binghamton University Binghamton, New York 13902 USA e-mail: dwilson@binghamton.edu keywords laughter, humor, emotional expression, nonverbal communication, contagion, mirror neurons, SMA, theory of mind, language, play, joy, multi- level selection, social neuroscience, positive psychology, evolutionary psychology, Duchenne, coordination He who approaches laughter upon science bent will find it no laughing matter. (McComas 1923:45) abstract A number of recent hypotheses have attempted to explain the ultimate evolutionary origins of laughter and humor. However, most of these have lacked breadth in their evolutionary frameworks while neglecting the empirical existence of two distinct types of laughter—Duchenne and non-Du- chenne—and the implications of this distinction for the evolution of laughter as a signal. Most of these hypotheses have also been proposed in relative isolation of each other and remain disjointed from the relevant empirical literature. Here we attempt to remedy these shortcomings through a synthesis of previous laughter and humor research followed by (i) a reevaluation of this research in light of theory and data from several relevant disciplines, and (ii) the proposal of a synthetic evolutionary framework