The quest for immortality

How long are we living now?

Longer than ever before. In 1900, much of the world’s population still led lives that were nasty, brutish, and short, and even in the U.S., the average life span was only 48 years for men and 46 for women. Only 4 percent of the U.S. population was over 65. Today, American men can expect to live to the age of 74 and women to 80. About 4.2 million Americans are 85 or older, and as many as 75,000 have reached their 100th birthday. Centenarians, in fact, are our fastest-growing age group; according to census projections, there will be at least 840,000 of them by the year 2050. “The notion is gone that we get three score and 10 and that’s it,” said Charlotte Muller of the International Longevity Center, an affiliate of New York’s Mount Sinai Medical Center.

Why is this happening?

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We’ve been pushing back the frontiers of death ever since the scientific revolution. For most of human history, periodic epidemics decimated entire populations, killing millions at an early age. That changed in 1798, when Edward Jenner developed his vaccine for smallpox, ushering in the modern era of immunization. Louis Pasteur’s germ theory of infection laid the groundwork for everything from sanitary operating conditions to pure water. Thanks to medical advances, people no longer routinely die from appendicitis, compound fractures, or in childbirth. Our present knowledge of nutrition and food preservation has wiped out famine in many areas of the globe. As a result of these advances, the human life span has increased more over the past century than in the previous 200,000 years.

Why do we get old?

Biologists have proposed four major theories. The wear-and-tear theory holds that the body simply corrodes, like a machine, due to toxins in our diet and environment, ultraviolet radiation, and physical and emotional stress. The neuroendocrine theory asserts that as we get older, our hormonal systems and organs stop functioning properly, and fail to provide the vital hormones and other secretions that keep bodies strong and healthy. The genetic-control theory posits that our DNA is programmed for death, once we fulfill our Darwinian destiny of bearing children, or reach age 40. The free-radical theory focuses on atoms with unpaired electrons, created as byproducts of the metabolic digestion of food. Free radicals are like little magnets that travel through the body, stealing electrons. They damage DNA, cell walls, and other important parts of the body.

Which of these theories is right?

The current scientific consensus is that aging is probably a function of all of these factors. Can science ‘cure’ aging? Up to a point. How far is a hotly debated question. The National Institutes of Health recently declared that science cannot extend the human life span beyond about 120 years. Steven Austad of the University of Idaho’s department of biological sciences is sure we can reach 150. Researchers from Cambridge University and Germany’s Max Planck Institute for Demographic Research are even more optimistic. They have calculated that ever since 1840, people born in any given year have generally lived three months longer than those born the previous year. The trend “is so linear,” they wrote earlier this year in the British journal Science, “that it may be the most remarkable regularity of mass endeavor ever observed.” The authors boldly concluded that “life-expectancy trajectories do not appear to be approaching a maximum.” This has led a few scientists to put the upper limit at 500 or even 1,000 years.

Is this the common view?

No. Most scientists believe that there’s a built-in barrier to longevity, called the Hayflick Limit. It’s based on the pioneering and sobering research of Dr. Leonard Hayflick, a cell biologist at the University of California, San Francisco. Throughout our lives, cells are constantly dividing and replacing themselves with new, genetically identical replicas. Hayflick found that cultured cells taken from the human body can’t divide more than about 50 times. At that point, the ends of their DNA strands begin to fray like shoelaces, and cancerous or defective cells are produced. The Hayflick Limit means that the body ultimately loses the ability to renew itself. “There is no evidence,” Hayflick says, “to support the many outrageous claims of extraordinary increase in human life expectation that might occur in our lifetime or that of our children.”

Can the limit be extended?

Possibly, through the magic of genetic engineering. Everybody knows some really old person who smokes like a chimney, doesn’t exercise, or scarfs junk food. Studies show that genes clearly play a major role in regulating aging and longevity. In 1993, a research project called the New England Centenarian Study began looking at 2,092 siblings of 444 people who lived to be 100. The results were published in June in the Proceedings of the National Academy of Sciences. It turns out that brothers and sisters of centenarians are, respectively, 17 times and 8 times likelier than the general population to reach age 100. “It helps prove what our parents and grandparents have told us for years,” said Dr. Thomas Perls, a Boston University geriatrician who headed the study. “Old age runs in families.”

How would an old-age gene work?

By blocking the damage caused by free radicals. Last year Dr. Jackob Moskovitz of the National Institutes of Health reported a gene that makes an enzyme known as MsrA. Moskovitz found that mice with this gene lived about 40 percent longer than those without it, because it protected them against the “oxidative damage” caused by free radicals. This discovery, he wrote in Science, “allows a glimpse into a world in which aging—and even death—may no longer be inevitable.” The next step, Moskovitz said, would be to engineer a mouse whose genes trigger a superabundance of MsrA. But it will be years before we know whether high MsrA levels are truly life-enhancing.

What about stem cells?

In the pursuit of longevity, they’re the real wild card. Stem cells are body cells that have not yet grown into heart cells, muscle fiber, nerve and brain cells—any kind of tissue in the body. It is stem cells that allow lizards to grow new tails, and humans to grow new skin over minor cuts. Embryonic stem cells, extracted from the spinal cords of human embryos, are the kind most prized by scientists because they can transform themselves into any kind of body cell. Unlike regular cells, which are subject to the Hayflick Limit, stem cells’ ability to divide is almost limitless. The world’s first embryonic stem cells have doubled their population more than 500 times since they were extracted in 1998.

So how can they help us?

If scientists can control the growth of stem cells, they could repair failing bodies the way a mechanic fixes an aging car—by installing brand-new, functioning parts. Stem-cell transplants could be used to treat dozens of serious ailments associated with aging, including cancer, Parkinson’s and Alzheimer’s diseases, diabetes, stroke, osteoporosis, and rheumatoid arthritis. And transplants of stem cells would only be the first step. In theory, entire organs could be grown outside the body: new hearts, new livers, new kidneys, and so on. When a part wore out or became diseased, people would not have to endure an agonizing wait for a donor organ to become available. They could simply go into “the shop” and get a new one.

How would these organs be grown?

The easiest way would be to breed animals that have been modified for this purpose. Pigs are the likeliest candidates because their organs resemble those of humans in terms of size and function. Researchers are currently trying to genetically alter pigs so that they don’t produce a sugar called alpha-1,3,-galactose. This sugar, found in many animals but not humans, invariably causes transplant recipients to violently reject animal organs. Cloning human tissue is another possible route. Scientists at Advanced Cell Technologies, which last year created the world’s first human-embryo clones, are now working on growing cow kidneys from cow stem cells. That would be a step toward enabling scientists to take human stem cells and grow anything from new tendons to new livers. “Within five years,” says Ben Bova, a futurist author of science fact and fiction, “we should see the field of organ transplants begin to change into the field of organ regeneration.”

Would that put an end to death?

No. These techniques would cure many diseases and prolong life, but they wouldn’t eliminate all the deterioration caused by aging. The human body is an enormously complex organism—far more complex than any machine. The Centers for Disease Control and Prevention estimates that even if 13 of the 15 leading causes of death were eliminated, the average U.S. life expectancy would increase by a year at most. Eradicating the other two, cardiovas-cular disease and cancer, would add 6.7 years and 3.4 years, respectively. So while 120 or even 150 looks likely, immortality does not.

What about the ethical implications?

They’re profound, but right now few people are giving much thought to how society will be affected if the average life span shoots up to 90, 100, and beyond. “We’re creating a big experiment,” says Dr. S. Jay Olshansky, a biodemographer at the University of Illinois’ Center on Aging, “a set of conditions that never before existed in our species.” In his new book, Our Posthuman Future: Consequences of the Biotechnology Revolution, Francis Fukuyama predicts that “generational warfare will join class and ethnic conflict as a major dividing line in our society.” Ubiquitous old age, he thinks, will turn all our expectations about the cycles of life and family on their ear. Instead of withering and dying as they used to, the elderly will increasingly “refuse to get out of the way; not just of their children, but their grandchildren and great-grandchildren.” There is also the question of overcrowding. In the next 50 years, our present population of 5.8 billion is expected to swell to 10.6 billion. And that’s before factoring in dramatically lengthened lives.

What might happen?

In the near future, intraspecies strife could erupt as the world ends up divided into three kinds of humans: the Enhanced, who will have computer chips blended into their brains, brand-new cloned organs, and other benefits of the biotechnological revolution; the Naturals, who would prefer not to avail themselves for aesthetic or ethical reasons; and the Rest, who are too poor to have a choice. The futurist Ray Kurzweil, winner of the National Medal of Technology and author of the forthcoming book The Singularity Is Near, predicts that by the year 2040, the Enhanced will be smarter, stronger, longer-lived, and in every measurable way superior to Naturals. Whether they’ll still be human is another question. At that point, the Naturals might adopt Nietzsche’s observation as their slogan: “What is great in man is that he is a bridge and not a goal.”