Mail and email of the species

Every week, it seems, social scientists find another way in which we divide ourselves into groups. There’s the Generation Gap, the Gender Gap, the Education Gap, people who shop at the Gap and those who don’t, omnivores and vegans, liberals and conservatives, book readers and Kindle readers, rock climbers and normal people, texters and grown-ups, gay and straight, rich and poor, black and white, boxer/briefs and a million other splits.