Nova: Science Now on PBS | “Where did we come from?” with host Neil DeGrasse Tyson explores the origin of our solar system and the start of life itself, how head lice figure in human evolution, and more. Journey back in time to the birth of our solar system to examine whether the key to our planet’s existence might have been the explosive shockwave of an ancient supernova. Meet a chemist who has yielded a new kind of “recipe” for natural processes to assemble and create the building blocks of life. And see how the head louse, a creepy critter that’s been sucking our blood for millions of years, is offering clues about our evolution. Finally, meet neuroscientist André Fenton, who is looking into erasing painful memories with an injection.