Athletic contests constitute an important aspect of human affairs. However, the evolutionary origins of athletic behavior, that is, behavior which is associated with participating in and watching athletic contests, are rather obscure, as they do not seem to contribute directly to increasing survival or reproductive success. This article argues that athletic behavior has been shaped in ancestral times jointly by intrasexual selection forces, where men look for potential allies, and intersexual selection forces, where men look for spouses for their female relatives. On the basis of this evolutionary framework, a number of hypotheses are derived: First, men are more interested than women in taking part in and watching sports. In addition, men are more interested than women in taking part in and watching competitive sports than non-competitive sports, and are more interested in team sports than individual sports. Finally, men and women differ in their motives for participating in sports, while the sex differences in athletic behavior between men and women are consistent across different cultures. Evidence from a sample composed of 37 different countries provides support for all hypotheses.