For decades, genetic testing has promised parents a way to avoid serious inherited diseases for their children. Now some Silicon Valley-backed companies are going much further, claiming they can help prospective parents not just avoid negative diseases, but choose the "best" embryo based on predicted intelligence, health, or height. Christopher Cox is a science writer for New York Magazine. He investigates the booming business of embryo screening, the anxiety driving parents toward it, and the ethical questions raised when reproduction starts to look more like optimization. His article is called Can You Really Choose Your 'Best Baby?'