Watch Sex: How It Works (2013) : Full Movie Online Free We've been doing it since we first walked the Earth. It gives us pleasure and it gives us life. But how much do you know about how sex works? Now, National Geographic Channel takes a fascinating look at one of the world's most popular pastimes: sex. Through gripping real-life stories and simulations, we journey from first times to playing the field, and all the way to humankind's ultimate goal, procreation. We'll learn anything and everything you've ever wondered about sex.