Earth teems with a staggering variety of animals, including 9,000 kinds of birds, 28,000 types of fish and more than 350,000 species of beetles. What explains this explosion of living creatures -- 1.4 million different species discovered so far, with perhaps another 50 million to go? The source of life's endless forms was a mystery until Charles Darwin's revolutionary idea of natural selection, which he showed could help explain the gradual development of life on Earth. But Darwin's radical insights raised as many questions as they answered. What actually drives evolution and turns one species into another? And how did we evolve? On the 150th anniversary of Darwin's "On the Origin of Species," NOVA reveals answers to the riddles that Darwin couldn't explain. Breakthroughs in a brand-new science --nicknamed "evo devo" -- are linking the enigma of origins to another of nature's great mysteries, the development of an embryo. NOVA takes viewers on a journey from the Galapagos Islands to the Arctic and from the Cambrian explosion of animal forms half a billion years ago to the research labs of today. Here scientists are finally beginning to crack nature's biggest secrets at the genetic level. And, as NOVA shows, the results are confirming the brilliance of Darwin's insights while exposing clues to life's breathtaking diversity.