Brain sex? John Money and Anke Ehrhardt proposed the idea decades ago. They drew the phrase from studies done on rats, birds, and the occasional primate. And the concept has had great staying power. Critics, myself included, have launched assaults on its edifice, but these have been repelled time after time. Today, if you let a computer search engine loose on the phrase, link after link turns up. There are books titled Brain Sex. There are self help guides to using knowledge about brain sex to advance one’s career. There are theories of primary and secondary education based on the premise that boys and girls have different brains. And more—YouTube videos by the title, critiques of the idea, BBC nature films on the topic. You name it! You can probably find it.