The average life span for Americans hovered around 40 years for the first 100 years of the nation's existence.
But after 1880, breakthroughs in modern medicine and public health resulted in a dramatic rise in life expectancy. By 1930, the average American could expect to enjoy an additional 20 years of life.
And today, of course, most Americans live considerably longer, around 79 years on average.
"It's an extraordinary thing that we can now expect to live long lives - unless we're extremely unlucky - and more than that, to be relatively high functioning," said Yale Law School's Samuel Moyn. "I'm interested in, let's say, the dark side of that. What are the unexpected consequences of having longer lives?
The answers to that question are the basis for his new book, "Gerontocracy in America: How the Old Are Hoarding Power and Wealth - and What to Do About It" (Farrar, Straus and Giroux).
