COULD YOU EVER LIVE FOREVER? - 4. The Secrets of Aging
Figure 1. Elderly lady.
Figure 2. Unlike humans, painted turtles can survive being frozen. Painted turtle babies can live for several days in this condition.
Figure 3. Genes determine a great number of human characteristics, such as skin color, eye color, and height.
Why do we age? What goes wrong as we grow older to cause our organs and other body parts to break down? There are several possible answers to this question. Scientists are trying to decide which one is correct.
According to one theory, some of the wastes produced by our body are harmful to us. Among these harmful substances may be a group called free radicals. When a free radical meets a chemical that is important to the proper working of our body, it may react with it and make it use less. Just as oxygen combines with the metal of a car to form rust, so free radicals may have a similar effect on our cells. The harder and longer our cells work, claims this theory, the more free radicals they produce. And the greater the number of free radicals, the more damage they cause to our body. Eventually, the damage is so great that we die.
Slow Down, Age Less
If free radicals do play a part in aging, slowing down the rate at which they are produced might help us to live longer. This would mean reducing the speed at which our bodies function.
On way to slow down the human body is to cool it. For example, before carrying out a heart transplant on a baby, doctors pack ice around the infant's body. This drops the body temperature to about 62°F. It also stops the beating of the heart and the movement of the blood. It is as if the baby were frozen in time. Yet, doctors must return the baby's temperature to normal and restart its heart within about an hour to avoid brain damage.
Humans cannot survive having their bodies chilled for long. But experiments on animals that can survive in this way have shown that a lower body temperature can increase the creatures' life span (see Figure 2). For example, flies kept at 64°F live twice as long as those kept at 86°F. Some species of frogs and turtles can survive when as much as half of their body water is turned into ice. Under these conditions, the animals show no signs of aging at all.
Since chilling will not work for humans, what other ways could we use to slow down the working rate of our cells? the results of an experiment at the National Toxicology Laboratory in Little Rock, Arkansas, may point to an answer. In these experiment, mice that received 60 percent less food than normal lived about twice as long as their regular life span. Also, as their life span lengthened, their immune system worked better, and they suffered less from disease. Some of the scientists who performed those experiments are so impressed that they have started eating less themselves. But they do not yet know whether reducing the amount of food people eat will help them live longer.
Other researchers think that glucose, a type of sugar found in our bodies, may be one main cause of aging. Glucose seems to make other chemicals, called proteins, stick together like chewing gum.
Proteins are the most important building blocks of cells and tissues. As we grow older, proteins in and between our cells become increasingly tangled, or cross-linked. This leads to many of the problems of old age, such as clogged arteries and damaged lungs. Recent laboratory tests have shown that glucose may have an important effect on cross-linking. People who suffer from diabetes, for instance, have a high level of body sugar. The victims of this disease live only about two-thirds the average life span of people with normal sugar levels.
Programmed to Die
Another theory of aging suggests that, from the moment of birth, our body cells contain "self-destruct" commands. These instructions, the theory says, determine when our bodies will wear out and break down.
All the instructions for controlling a cell are contained inside tiny chemical structures called genes. The genes are joined together on long, coiled strands. A complete copy of all your genes exists inside every one of your cells.
Your set of genes determined characteristics such as your eye and skin color and height, as well as every chemical process that is needed to keep you alive (see Figure 3). Some scientists now claim that certain of your genes also decide when you will die.
To pinpoint the genes that may be responsible for aging, researchers are studying people who have a rare condition known as Werner's syndrome. This affects about one in a million babies.
Children who have Werner's syndrome begin to age very rapidly. A 10-year-old may have the wrinkled skin, shrunken muscles, and baldness of an old person. Few victims survive beyond the age of 20.
Research has shown that about 40 or 50 genes in children with Werner's syndrome are working much faster than normal. These may be the genes that are responsible for aging in all human beings. The next step is to study these "aging" genes in more detail to find out exactly what they do. Then researchers may be able to alter them to slow down the aging process.
In 1990, a team of Japanese and American scientists announced the results of another important research project. They took normal human cells and combined them with cancer cells from hamsters. Normally, cancer cells go on dividing endlessly, even in a laboratory dish. In a sense, cancer cells live forever. But when the researchers mixed the normal human cells with the cancerous hamster cells, they found that the cancer cells died. Something in the normal cells caused the cancer cells to age and wear out. Eventually, the researchers traced the aging effect to the action of one particular gene. Now, the scientists are focusing on this gene, trying to discover exactly how it works.
In other laboratories, scientists have managed to breed long-lived strains of certain small animals. At the University of Colorado, researchers carried out an experiment with a type of worm known as a nematode. Choosing the oldest nematodes for breeding produced long-lived offspring. The new generations of nematodes differed by only one gene from their normal, short-lived cousins. Does this gene correspond to the human aging gene that kills cancer cells? Within the next few years scientists may find the answer.
|Brains That Last Forever
In a strange way, a person might live forever if his or her brain were replaced by a computer. Some scientists believe that the brain itself is like a computer. Already, researcher has begun on a new type of computer, called a neurocomputer, that works in some ways like the brain. If this research is successful, it may be possible in the future, to link a neurocomputer directly to the brain. That would give a human being extraordinary new powers.
For example, the person could store a huge amount of knowledge or calculate extremely fast using the attached neurocomputer. As time went on, more and more of a person's thoughts could be held inside the computer. Every important part of the person's mind could be transferred to the machine, In that way, when his or her brain dies, the person would live on inside the computer.
An End to Death?
No medicines are on sale yet that will help you live longer. But studies have shown that the way a person lives can have a major effect on his or her life span. Overeating, a poor diet high in animal fats, smoking, and stress seem to shorten a person's life. Low-fat, high-fiber diets, exercise, and plenty of rest tend to keep a person youthful and healthy.
Meanwhile, doctors are making rapid progress in the war against disease. Many forms of cancer, for instance, can now be successfully treated. New methods in the operating room have made it possible for surgeons to mend damaged hearts and other organs without endangering their patients' lives. Organ transplants have become increasingly common and successful. In time, artificial organs will be available that perform as well as real ones.
All these advances are helping to increase the average life span of people in the developed world. But the biggest breakthrough will come when scientists find the basic reasons why our bodies age. Researchers appear to be on the brink of discovering which particular gene or genes in our cells is responsible for aging. It should then be possible to alter those genes so they are no longer active.
So, could you ever live forever? If not forever, scientists say, then for a very long time. Within the next century, life-prolonging medicines are likely to be available in local drugstores. Some of these may "switch off" our aging genes. Others may prevent he buildup of harmful substances such as free radicals. Such drugs and other methods of slowing aging will become more and more effective. As a result, human beings may eventually live to be hundreds or even thousands of years old. Today, no one knows what effects these changes will have on future generations of life on Earth.