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. Last Updated: 07/27/2016

The Cost of a Long Life

My grandmother lived vigorously to the age of 100. She was raised in an impoverished shtetl in tsarist Russia, arrived in America the day McKinley was shot, lived in a cold-water tenement, sewed garments in a crowded, filthy sweatshop and delivered four children at home. I always assumed she carried genes for longevity and a strong constitution. There were some in her family, similarly healthy and long-lived, who inherited those genes, and others, less blessed, who did not.

It was a matter of good fortune, and nothing fundamental could be done to alter the outcome. Yet as we look into the next century, we see science poised to determine a person's life span directly, by modifying his genes. Pills would replace parents as the key to vigorous longevity. Although providing long and healthy lives is a laudable goal, the consequences of this approach raise deeply disturbing questions.

Genes for long life were first found in fruit flies. Last month, a breakthrough occurred in higher animals. Mutant mice were created, through genetic engineering, that lacked a normal cell protein called SHC. All mammals, including human beings, have this SHC protein. The mutant mice were healthy and lived one third longer than their normal counterparts. Their cells were notably resistant to oxidants, molecules that wear down tissues the way they rust metal. Of course, we are not mice, and the SHC protein may not have the same effects on oxidation in our cells. But the proof of principle is powerful. Analogous genetic changes in people could routinely make us into centenarians.

Genetic diagnosis, though, will come before any specific treatment. People will learn of their natural chances to live to a certain age and their risks of having a variety of diseases. This knowledge will make it increasingly urgent to create drugs to modulate the effects of genes linked to illnesses. Such drugs will be designed, in large part, using supercomputers that will screen chemicals, to see which ones might work, in a virtual format before empirical testing in cells and animals.

The natural and steady degeneration of tissues is accelerated by disease.

Illnesses become deadly when they overwhelm the body's defenses and its mechanisms for repair. Longevity appears to involve delaying normal aging while protecting against disease.

Data on centenarians published this year suggest what is needed to live past 100. Many centenarians had close relatives in their 90s and early 100s. They were like my grandmother, physically and mentally vigorous, and were largely free of illness until shortly before their deaths. Their survival apparently involved not only genes for longevity, but also genes that reduce susceptibility to disease.

The converse painfully makes the same point: Families with genes that predispose them to serious illness, like the genes for breast cancer or the hyperlipidemia genes for heart attack and stroke, are marked by untimely deaths.

We will be faced with the difficult decision of which life-limiting genes and proteins to remedy first. Should we address the most prevalent killers, like atherosclerosis, or the maladies that affect younger people, like juvenile diabetes? Will some racial and ethnic groups be given short shrift, since minorities often have unusual genes predisposing them to rarer disorders? Will diseases that happen to affect congressmen, celebrities and corporate chief executives be favored, getting periodic infusions of money for research and development?

No one believes that anyone should be denied the benefits of science for financial reasons. So, even after priorities are set, who will pay for the longevity treatments, which probably will begin at an early age and extend 100 years or more? Certainly the drugs will be costly, but might health costs ultimately be reduced if we can successfully delay illness and extend productivity for five or more decades? Will the process of dying also become less costly, since it may occur rapidly as the drugs wane in effect or are withdrawn, in contrast to the slow, stuttering decline that is now the expensive norm?

Regardless of who is first in line, and regardless of the cost-effectiveness of the treatments over time, only those in wealthy and prosperous nations will have access to them. This will make global demographics even more lopsided than they are now, as people in the United States and Europe live well past 100 while Africans and Asians continue to die young, as they have for centuries.

In the industrialized world, family dynamics will change as five or more generations know each other. The ballooning healthy population will sharply increase global demand for food, shelter and everything else. The natural resources and cheap labor to respond to these material needs will come from the developing world, as they do now, but the drain from those areas will be magnified. Unless the rate of new births slows, we will have Malthusian strife within a Methuselahan culture. Will a limitation on reproduction be voluntary or become coercive?

The quest for longevity holds a tight grip on the human imagination, forming the fabric of ancient myths and the core of explorers' dreams. A long, vigorous life is posited as the solution to much of our suffering and many of our dilemmas. Yet as science brings this goal into reach, the inequalities of the past and the present threaten its realization. We disregard these issues at our peril.

Jerome Groopman is a professor of medicine at Harvard University. He contributed this comment to The New York Times.