The New York Times produced a couple of fascinating stories about how the past century has produced Americans substantially taller, heavier, healthier and longer-lived.
Obviously, evolution itself does not change the shape of humanity in a mere century the way obesity does, and obesity may, it is speculated, become the tipping point (so to speak) for a reduction in life expectancy. Despite quantum growth in our understanding of genes, we still don’t know how much of our fate is written in our DNA and how much is a function of behavior.
A variety of studies indicate that middle-age health, the delay of fatal illness and ultimate longevity are consequences of nutrition in utero and through the first two years of life — which has implications for education, environmental and public health policy.
How we take care of ourselves may or may not have much to do with longevity, but focusing on a number of years as some kind of entitlement is probably the wrong way to look at our diet and fitness needs. The object should not necessarily be to live until 100 but to be able to squeeze as much enjoyment and productivity out of what number we are given before it comes up.