Quick, name the world's oldest profession! It's not what you think, say the authors of The Invisible Sex. The world's oldest profession is, most likely, midwifery. The combination of larger brains and narrower pelvises required adaptations that led to women no longer being able to give birth solo. The book's title itself illustrates the thesis: were women truly invisible in societies of the past, or did they become so because of anthropologists' biases?