Let’s consider the case of identical twins who were similarly active as kids. But over the past three years of their adulthood, one of them has exercised regularly, and one of them hasn’t. Would there really be much difference in their fitness levels and overall health? Or, in the end, does it really all come down to genetics? The NYT’s Gretchen Reynolds reports on a recent study in which “it turned out that these genetically identical twins looked surprisingly different beneath the skin and skull. The sedentary twins had lower endurance capacities, higher body fat percentages, and signs of insulin resistance, signaling the onset of metabolic problems … The twins’ brains also were unalike.”

+ Kevin Roose in Fusion: “I tried Silicon Valley’s favorite brain-enhancing drugs.” (I miss the days when this town still ran on coffee, egomania, and greed.)