Dr. Robert Butler, 81, says he felt a need to "sum up" all he has learned in 50 years of studying longevity.

"This was a hard book to write," he says of his massive tome, "The Longevity Revolution," (Public Affairs, 2008).

"There is a paradox. On one hand, longevity is a great human achievement and on the other are the gloomy people who think we can't afford old age."  To Read The Interview...