Watch The Shape of Life Season 1 Episode 8 Online

As we go through our lives — driving cars, exploring the Internet, studying the world around us — it is hard to imagine that we're related to Earth's other animals. It's even a stretch to see what connects us with the rest of the chordates, a group of about 50,000 species including the vertebrates like fish, amphibians, reptiles and birds, mammals and ourselves. But indeed, all chordates, from the worm-like amphioxus to Homo sapiens have three common features.