Is it a boy or a girl? When it comes to personal identity, gender is so foundational that it is often the first thing we ask new parents when we learn that a human being has entered the world. But as the behavioral sciences have revealed, gender is not the simple binary matter implied in that age-old question. Nor is it so easy to determine from a child's visible anatomy. For an estimated 0.3 percent of people in the U.S., external appearance feels like a terrible mistake.

In a sensitive and deeply reported cover story that begins on page 26, journalist Francine Russo examines the latest research and an ongoing debate among clinicians about how best to help children and adolescents with gender dysphoria—what experts describe as the “insistent, consistent and persistent” sense that one's sex is not what was written on the birth certificate. Some children make this known almost from the moment they can speak. “Mama, something went wrong when I was in your tummy,” one three-year-old told a mother interviewed by Russo.

Knowing how—and especially when—to intervene for such young people is a fast-shifting frontier of medicine—one with even more ethical and cultural minefields than are faced by transgender adults. “I found it so wrenching for both the kids and their parents,” Russo says of her reporting experience. Fortunately, she notes, “good futures are now possible, especially if they get help early.”

In this first issue of 2016, we continue the proud, 170-year-old Scientific American tradition of offering articles written by leading scientists. In an article beginning on page 36, Stanford University psychologist Carol S. Dweck updates her influential research on “growth mind-set”—the belief that your intelligence is not fixed but can be developed through effort. Dweck walks us through a riveting array of recent studies that demonstrate the influence of personal mind-set on student learning, organizational success and even political peacemaking.

Can you be addicted to the Internet? How about sex, eating or video games? Columbia University psychiatrist Carl Erik Fisher sizes up research on “behavioral addictions,” adding insights from his clinical practice.

Who among us doesn't hope to bring creativity to whatever work we do? In an excerpt from their new book Wired to Create, University of Pennsylvania psychologist and Scientific American blogger Scott Barry Kaufman and journalist Carolyn Gregoire examine research on the traits, brain chemistry and habits of mind that power invention.