Over tea at her north London home, Aarathi Prasad is talking calmly, coolly, about reproduction. But not sex. Specifically not sex. Her subject is technologies that would take intercourse out of the reproductive equation, advances that could challenge everything we know about family and the relationship between men and women. Their potential is summed up in the final paragraphs of her new book, Like a Virgin: How Science is Redesigning the Rules of Sex.