While talk of sex is all around us, the fact is that  the origins of our reproductive lives are still a mystery.  And while 50 years ago Masters and Johnson set out to try and find the science of sex, much has transpired since in our understanding of science, and evolutionary biology.In his new book  How We Do It: The Evolution and Future of Human Reproduction Field Museum of Natural History curator Robert Martin draws on 40 years of research in biological anthropology to locate the roots of everything from our sex cells to the way we care for newborns. He examines the procreative history of humans, as well as that of our primate kin. His findings are a constant surprise.My conversation with Robert Martin: