Rhythmic Entrainment and Sexual Selection in Animal Communication

In animal behavior, entrainment is the specialized sensorimotor process by which individuals precisely coordinate endogenous ultradian (period <10 s) rhythms with those of their conspecific neighbors. The rhythms are typically communication signals, either acoustic, substrate vibration, or optical, that are distinguished by their continuous isochrony (consistent repetition rate), and the expressed coordination is synchronous or antisynchronous (alternating) alignment. Entrainment is known in orthopterans, cicadas, fireflies, crabs, frogs, birds, and humans, where it is a core element of musicality and related group activities. Animals, including humans, achieve entrainment by adjusting rhythm phase, which is adequate if several individuals have comparable tempos (repetition rates), or by adjusting both phase and tempo, if their tempos differ. In the latter case, temporal alignment can be very precise. Entrainment has not yet been reported for natural populations of nonhuman mammals, notably primates-suggesting that human entrainment evolved de novo in the hominid lineage within the past 5 million years. Experimental studies on the function and adaptation of entrainment in arthropods and anurans can offer clues to its origin in humans.