Male and female tungara frogs. Among these frogs, the guy with the best call usually wins the gal — except when you throw a third-choice loser into the mix. Alexander T. Baugh/Encyclopedia of Life hide caption

itoggle caption Alexander T. Baugh/Encyclopedia of Life

Margaret Sanger appears before a Senate committee for federal birth-control legislation in Washington, D.C., on March 1, 1934, arguing that federal courts be given the right to discuss contraceptive methods with their patients. Anonymous/AP hide caption

itoggle caption Anonymous/AP