This is not an idle concern, or merely fodder for science fiction--like Logan's Run, in which they not only don't distrust people of 30, they kill them, or Soylent Green, in which the dead become food. In the real world, policy makers are increasingly concerned about whether we can afford our aging population. The baby boomers, of which I am a proud charter member, were born between 1946 and 1960. During this period--all those GIs back from World War II--the U.S. fertility rate was twice its 20th century average. Today we constitute almost one-quarter of the population.

In 2006, Social Security cost us about 4.2 percent of the Gross Domestic Product (GDP)--$554 billion. By only 2030, it will grow, as a percentage of GDP, by 50 percent to 6.2 percent. And it will keep rising. Sooner than that--if nothing changes--by 2017, payroll taxes will collect less for Social Security than it needs to pay out.

Medicare, which pays for the health care of 43 million aging or disabled Americans, potentially faces an even more dire future. Today, Medicare is a $230 billion annual program--about 3 percent of GDP. But by 2018, Medicare will cost more than Social Security.

This is not an impossible problem. In the U.S., if we can develop the political will to increase taxes, for example, we could sustain Medicare and Social Security well into the 22nd century. Currently, the payroll tax of 6.2 percent is imposed on only the first $106,800 of income. Simply raising this income cap, says Stephen Gross, the Social Security Administration's chief actuary, could--depending on benefit increases--cover 93 percent of the current shortfall or even produce a surplus over the next 75 years.

Alternatively, if 60 is the new 50, we could help solve this problem by putting the money where our mouths are, by raising the eligibility age. When Social Security was enacted in the 1930s, the average U.S. life expectancy was less than 65. Far fewer people were expected to live to collect the benefit, or to live for decades beyond 65 as millions do today. Raising the age to 70, by one estimate, would not totally eliminate the projected shortfall, but eliminate more than third of it--by 36 percent.

Similar, although not identical, considerations apply to Medicare. If we rose the eligibility age without providing any additional access to medical insurance, it could actually increase costs with more people flooding expensive emergency rooms. But raising taxes--according to most scenarios--would cover projected shortfalls from our current tax structure.

Other countries--particularly other advanced countries that have a more developed social welfare system than we do--face potentially greater crises. Even though Europeans with more munificent social welfare programs pay more taxes, the U.S. is not at the same disadvantage when it comes to population demographics. We continue to have a fertility rate that allows us to maintain or even increase our population, providing more folks to pay for my retirement. The replacement fertility rate--that needed to keep the current population stable--is 2.1 lifetime births per woman. The U.S., with a fertility rate of 2.1, is one of the few industrialized nations above the replacement rate. If we add to that, immigrants--both legal and undocumented, who pay taxes too--we have less of a problem than some of our competitors.

Contrast that to European countries. You might think it's only the godless Scandinavians who have low birth rates, but the godless Italians and Spaniards predominate here. Paradoxically, these Catholic countries have the two lowest fertility rates in the world, only a bit more than one child per woman at 1.2. Having the Pope in your backyard or being the home of the Inquisition doesn't seem to count for much these days. It's possible that in their preindustrial, agrarian, eras having many children were needed for labor intensive farm work, and were seen as a kind of old-age insurance in the absence of government or private pension. Today, the higher taxes that fund social welfare programs may be a deterrent to the affordability of more than one child. In Scandinavian countries, which have a higher fertility rate, although still below the replacement level, the higher level of benefits may be less of a deterrent to having more children.

To offset this problem, Italy has enacted a cash benefit of 1,000 Euros for women who have a second child. In Japan, which has a replacement birth rate of only 1.37, the new government plans to pay families $237 each month per child until they reach the age of 12.

Such policies are quite different from China, which penalizes families who have more than one child, or poor countries that continue to have high fertility rates, and wish they had the demographic problems of either the U.S. or China.

In the U.S., Europe, and Japan, these demographic considerations, at bottom, require only a bit of not too painful tweaking of benefits via retirement age, tax rates, or benefits for fertility. But what if science advanced to the point where life expectancy took a quantum leap or we became immortal? How would we cope with all those 200 and 300-year-old people?

In a previous post, "Will A Quantum Leap In Longevity Make Us Paranoid?" I wondered whether an indefinite life expectancy would make us over protective of a commodity--longevity--which would greatly increase in perceived value. I pointed to Isaac Asimov's fictional planet, Solaria, in which restrictions were placed on fertility, robots did all the work, and people lived in reclusive, protective isolation.

Psychological consequences aside, Leonid Gavrilov, in "Demographic consequences of defeating aging," (presented at the Strategies for Engineered Negligible Senescence Conference, Queens' College, Cambridge, England, September, 2009) asks: "Is it possible to have a sustainable population dynamics in a future hypothetical non-aging society?"

In computer simulations, Gavrilov concluded that "population changes are surprisingly slow in their response to a dramatic life extension. For example, we applied the cohort-component method of population projections to 2005 Swedish population for several scenarios of life extension and a fertility schedule observed in 2005. Even for very long 50-year horizon, with the most radical life extension scenario (assuming no aging at all after age 50), the total population increases by 35 percent only (from 9.1 to 13.3 million)."

Paradoxically, the population might even decline "if some members of the society reject to use new anti-aging technologies for some religious or any other reasons (inconvenience, non-compliance, of side effects, costs, etc.)."

Immortal parents, if they had only one child per couple, would double the population over time. The population would not grow infinitely.

"In other words, a population of immortal reproducing organisms can grow indefinitely in time, but not necessarily indefinitely in size, because asymptotic growth is possible," Gavrilov said in an interview with Rejuvenation Research (Volume 12, Number 5, 2009).

"The startling conclusion is that fears of overpopulation based on lay common sense and uneducated are, in fact, grossly exaggerated."

He adds: "In brief, we found that defeating aging, the joy of , and sustainable

population size are not mutually exclusive. This is an important point, because it can change the current public perception that life extension necessarily leads to overpopulation."

Of course, one person's under population may be another demographer's nightmare. A doubling of the population would require commensurate increases in to sustain a reasonable quality of living.

But if we were immortal--something I don't expect in my own lifetime, although I might wish it on my children who could be saying either "poor, mortal dad" or "I'm bored" centuries from now--we would save all those trillions on what would be a useless Medicare program.

We might have to spend some of those trillions on safety since immunity from aging and disease won't protect you from wrapping your car around a tree on the side of an icy road.

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My book, Nasty, Brutish, and Long: Adventures in Old Age and the World of Eldercare (Avery/Penguin, 2009) provides a unique, insider's perspective on aging in America. It is an account of my work as a psychologist in nursing homes, the story of to my frail, elderly parents--all to th accompaniment of ruminations on my own mortality. Thomas Lynch, author of The Undertaking calls it "A book for policy makers, caregivers, the halt and lame, the upright and unemcumbered: anyone who ever intends to get old."