PBS
Pbs Learning Media: The Transforming Leap, From Four Legs to Two
John Noble Wilford, a "New York Times" science writer, outlines various hypotheses on the origin of bipedalism.
Smithsonian Institution
National Museum of Natural History: What Does It Mean to Be Human, Human Characteristics
Explore walking upright, tools and food, bodies, brains, social life, language and how humans ultimately changed the world. Excellent charts, pictures and videos accompany easy-to-understand text on the earliest humans.
Australian Broadcasting Corporation
Australian Broadcasting Corporation: News in Science: Walking Upright Started in Trees
From ABC News in Science, Will Dunham's article on orangutans covers topics related to the evolutionary process of "bipedal walking," or walking on two legs instead of four.