Life expectancy predictions, however, in order to be accurate, need to factor in the negative, as well.
"Every once in a while," says Olshansky, "a novel source of data surfaces that makes it possible to peer into the future in a fundamentally different and far more revealing way."
Case in point: a study of 3,237 young Minnesotans who died between 1981 and 2004. Their autopsies revealed that while the severity of coronary heart disease had declined from '81 to '95, the trend had reversed itself after 2000, owing to an increase in obesity, among other factors.
Insurers and other longevity predictors, he says, make a mistake not to consider negative lifestyle factors. The Minnesota data, in his view, offers "a glimpse into the future of heart disease" in tomorrow's adults.
Unlike many of his peers, he does accept it as a given that tomorrow's Americans will live longer than today's. More likely, he thinks, they will hit a "longevity wall" at age 85.
Even if science were to find a cure for cancer and for heart disease, Olshansky says, the average human lifespan won't advance beyond 90, unless someone finds a way to slow the aging process itself.
That search is underway at a variety of laboratories around the country, including at Sierra Sciences in Reno, Nev. Sierra's motto: "To cure aging or die trying."