There’s an old joke where someone tells a guy that his bad habits could cut 5 years from his life, to which the guy responds, “Yeah, but which 5 years?” It turns out that over the past several decades, humans have seen a lifespan increase in total years, and in active years. “Imagine, now, that the trend of the last century continues another hundred years: Our 50-year-old great-grandchildren may have an average of 50 years left to live, the same span as a 30-year-old today can expect. It is not implausible that they will be similarly spry and untouched by disability.” In Nautilus, David Steinsaltz wonders: Will 90 Become The New 60? (I’d be satisfied if I could figure out the point of SnapChat.)