There’s something uncomfortably sterile about life-expectancy rates. When the Centers for Disease Control and Prevention reports that average American life expectancy shortened by a tenth of a year, as it did last year, it’s forgivable if the problem isn’t immediately obvious. Sure, we might have shaved off a little more than a month from our lifespans, but at the same time, mortality rates for some of America’s leading causes of death, including cancer, heart disease and kidney disease, are falling.