EXCERPT: A physicist trained at Caltech and Cambridge, he sees immortality as a mathematical challenge. To solve it requires first asking why we age. “The canonical answer,” Fink explained, “is that aging is inevitable and a fundamental condition of life.” Every organism degrades over time and eventually breaks down. End of story. “But the story’s much weirder than we think,” Fink said. In a recent paper, he used math to demonstrate that “aging can be favored by natural selection.” That’s a shocking insight: It means that the first forms of life, which started billions of years ago, likely didn’t die....