To celebrate the 50th anniversary of Born Free, Joy Adamson's memoir about rescuing Elsa the lion cub, PBS's "Nature" series examines the lives of Joy and her husband, George, and the long-term impact of their environmental efforts on African lions. Virginia McKenna, who played Joy in the classic 1966 film, shares her memories of the Adamsons, with home movies and diary entries further illuminating their struggles to promote conservationism.