In 2016, Lisa Littman, ob-gyn turned public health researcher and mother of two, was scrolling through social media when she noticed a statistical peculiarity: several adolescents, most of them girls, from her small town in Rhode Island had come out as transgender—all from within the same friend group. “With the first two announcements, I thought, ‘Wow, that’s great,’ ” Dr. Littman said, a light New Jersey accent tweaking her vowels. Then came announcements three, four, five, and six.
