Pirouettes: the rotational play of wild chimpanzees.

A pirouette is a locomotor-rotational movement in which a young chimpanzee spins around in a (mostly) quadruped posture while advancing forward in a straight line. We addressed whether this behavior evolved as a practice of general athletic ability or of sexual selection. The former hypothesis would predict no sex differences in skill or the developmental process, while the latter would predict the opposite. Chimpanzees most likely master the pirouette around the time of weaning. We found no conspicuous sex differences in the developmental process or the number of rotations per bout of pirouettes, so the pirouette's main function may be to facilitate general athletic ability. Infants pirouetted regardless of the context of rest or travel, whereas juveniles and adolescents pirouetted primarily during travel. This is consistent with the survival strategy hypothesis, because juveniles and adolescents would be expected to display pirouettes to many watchers if this practice were sexually selected. However, the fact that males tend to pirouette faster than females and to pirouette even during adolescence suggests that sexual selection has some influence in shaping the evolution of the practice. Despite this, no conspicuous tendency was found for juveniles or adolescent chimpanzees to display pirouettes to opposite-sex individuals. More data on adolescent individuals are needed to definitively determine the role of sex differences in pirouetting behavior.