The Evolutionary Dynamics of Friendship and Body Odor

The city remains Ukraine’s only provincial capital to be taken by Russian forces—can Ukraine overcome its shortages of manpower and firepower to retake the province? Mexico’s official missing-persons list has topped 100,000; our correspondent describes the skyrocketing total and piecemeal efforts to slow its rise. And research suggests that people choose their friends at least in part by smell. For full access to print, digital and audio editions of The Economist, subscribe here www.economist.com/intelligenceoffer