How can he, when 40,000 elephants are still slaughtered for their tusks every year? When — despite his best efforts — transnational trafficking rings continue to smuggle ivory and other wildlife contraband with impunity? It’s especially maddening for Wasser, director of the Center for Conservation Biology at the University of Washington, because he thought he had a solution: a DNA fingerprinting method that took years to develop and has the power to trace ivory back to its geographic origins. In 2015, Wasser and his colleagues used the technique to pinpoint the worst poaching hot spots across Africa — and waited for the crackdowns to follow. But some nations responded with shrugs or denials, while others lack the money and manpower to do much about it. So Wasser lies awake at night, his mind churning, trying to figure out more effective ways to attack the problem. Sometimes a new insight will jolt him out of slumber. Many nights, stress is the sleep-killer. The stress of scrambling for grants to keep his lab afloat, of trying to cajole officials in Mombasa or Singapore or Côte d’Ivoire to let him sample seized ivory for DNA testing, of watching known traffickers walk free. Sitti...