We humans just weren't designed to sit on our tushes all day; the static, unnatural posture is hard on the spine, degenerative for the muscles and hindering for circulation. But since we do, designer Henner Jahns (you guessed it, he's one of those crazy German-engineer types) has developed a chair that's better for you. The Swopper is actually a cushy, back-less seat set atop a fully articulating base. The convex seat shape impels correct posture and spine alignment, while the base's up-and-down. . .