eter Turchin, one of the world’s experts on pine beetles and possibly also on human beings, met me reluctantly this summer on the campus of the University of Connecticut at Storrs, where he teaches. Like many people during the pandemic, he preferred to limit his human contact. He also doubted whether human contact would have much value anyway, when his mathematical models could already tell me everything I needed to know. But he had to leave his office sometime. (“One way you know I am Russian is that I cannot think sitting down,” he told me. “I have to go...