The greatest certainty in life is death. As we grow old, our muscles and bones weaken, our skin wrinkles, and our eyesight and hearing become less keen. In time, as with a worn-out car, some important part of our body breaks down completely. Then we die. But does this have to happen? Are there ways in which human aging could be slowed or stopped altogether?

Why do living things die? It would seem much better for an animal or plant if it could grow up and then stay fit and healthy without aging any further. But this would not be good for the species, the type of animal of plant, to which the individual belonged.

Death seems to be nature's way of getting rid of creatures that have outlived their usefulness. For instance, lions that have lived long enough to have offspring of their own have served their main purpose. They have helped to ensure the survival of their species. But if lions never died, the world would be overrun by them. And the same is true of other species. If individual animals or plants could live forever, the Earth would quickly become overcrowded.

Why does every living thing eventually die? One possible answer is that the body's defense system breaks down. Instead of destroying only invaders such as germs, the defense system may attack parts of the body which are healthy.

There is another possible answer. Something may go wrong with the chemical instructions that tell the body how to repair and maintain itself. While we are young, these instructions are carried out without a mistake. As each tiny living unit, or cell, in our body dies, it is replaced by an exact copy. But as we grow older, the chemical instructions may be partly lost or imperfectly passed on. Some cells are not replaced. Others are replaced with faulty ones. As a result, we age. Our bodies develop serious problems, and we die.

Dying for a Cure

If we knew the exact causes of aging and death, then perhaps we could find ways to counter them. Some causes of death are known. There are accidents. People are killed, for instance, by drowning or falling off mountains. There are also many diseases, such as cancer, which can kill people before they die of old age. Thus, the average human life span could be increased by making the world safer and by finding cures for deadly diseases.

But even if all these obvious causes of death were removed, human beings would not live forever. Our bodies eventually wear are. One way to solve this problem would be to replace the worn parts with new parts made of artificial materials. A diseased heart, for instance, could be replaced by one built from plastic and metal.

It would be even better, though, if scientists could discover the basic causes of aging. They might find out why our bodies start to break down as we grow old. Then, further research might show how to greatly slow or stop the aging process.

So, could you ever live forever? Maybe you would not want to live that long. Or perhaps you would look forward to all that you could see and learn during a healthy lifetime of hundreds or thousands of years. In the not-too-distant future, people may have that choice.