My guest today is Helen Joyce. Helen is a staff journalist at the Economist magazine, and has been an editor there since 2005. She also has a PhD in mathematics from University College London. Helen just released a controversial new book called "Trans: When Ideology Meets Reality." Now, this is one of those books that is likely to be misrepresented on Twitter and in some media as transphobic but is in fact a deep and thoughtful attempt to navigate all the complex issues at the intersection of gender identity and public policy.  Helen and I discussed the difference between gender and sex, evolving definitions of gender, the different waves of feminism, gender dysphoria and related phenomenon like autogynephilia, trans identity as well as gender neutrality. We talk about hormone treatments, puberty blockers, detransitioning, and the age at which people should be able to make these kinds of decisions. We discuss gender pronouns, the logic of sex-segregated spaces, such as locker rooms...