The relative life expectancy of a 7-footer is foggy, but scientists do know that a human being's medically optimal height is considerably closer to 6'1" than it is to 7'1". Grow nearer to the latter mark, says John Komlos, an economist who studies height at Ludwig-Maximilian University in Munich, and "health diminishes: back, heart, bones. Mortality rate rises." Adds Gowriharan Thaiyananthan, co--medical director of the Chapman Neurosurgical and Spine Institute in Orange, Calif., and a neurosurgeon who's operated on four 7-footers himself, "Our bodies were not designed to be 7 feet tall. That's like turning a car into a stretch limo: Things work, but it's not what nature decided is our optimal state. You're pushing every organ system to its limit."