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Yawning, that universal signal of boredom and sleepiness, is so
contagious that merely reading this article will inspire many
readers to yawn. The neurobehavioral basis of yawning and its
contagious nature are well understood, yet certain myths
persist—for example, the belief that yawning is a response to
oxygen deprivation. In fact we begin yawning in the womb, and most
vertebrates yawn; yet contagious yawning is confirmed only in humans
and chimps. Yawning may a tool for studying the roots of social
behavior and of certain pathologies such as autism and schizophrenia.