The first time Rikki Carver pressed a stethoscope against a rhino, the jungle fell away. Deep in Borneo, in a former coal mine that had been painstakingly reforested into a sanctuary, the air was thick, the forest quiet. But all Rikki really heard was the steady, deliberate thump of a heart that might not have a successor. Pahu, the Sumatran forest rhino resting in front of her, is one of just two of her kind left on Earth. “Listening to her heartbeat,” Rikki said, “I remember thinking this is probably something I’ll tell my grandkids about. You’re hearing the heart of an animal that might never have another baby, that might be the last one of her species. There’s a weight to that. But it also kind of re-instills why you’re doing this. You realize, this matters.” “It felt like listening to the heartbeat of a planet,” she said. “Like something sacred.” For a sophomore on the Cornell women’s track and field team, it was a long way from home. The girl who once turned her family’s la...