Last week, a federal judge blocked an order from the Obama administration mandating that public schools nationwide allow transgender students to use bathrooms that correspond with their gender identity. Earlier in the summer, the U.S. legally recognized the first non-binary person, someone who identifies as neither male nor female. Both of these stories highlight the latest chapter in how our understanding of gender is changing—and the corresponding unease many have with it. What it means to be a man and a woman, and evolving perspectives on gender and sex.