Vincent van Gogh was an artist, and a famous one. However, to many people who never have seen his paintings he is better known as the man who one winter's day in 1888 cut off his own ear.

Did he have a right to do it? How about his toe, or his hand? To what extent did he (or you, or I) own his own body? This question has never been fully answered, though we know of some restrictions. For example, suicide is illegal in most of today's societies, while the right of a terminally ill patient to die depends on where he or she lives.

I believe that the arguments over your rights to your own body have scarcely begun. In the next twenty years, no issue will be more controversial or hotly debated. The present furor over stem cell research is no more than the first shot in a long war.

This article will not tackle the complex legal, ethical, political and social issues. My objective is merely to clear the ground, so to speak, by providing basic scientific facts which ought to (but seldom do) precede other arguments. For example, one undeniable fact is the limited power of humans to regenerate body parts. We can grow new skin, but not a new finger or toe, or new nerve cells. Since amphibians can grow whole new limbs and lizards new tails, we know it can be done. If we could learn the regeneration trick and use it in humans, our approach to everything from spinal cord injuries to Parkinson's disease and Alzheimer's disease would be transformed.

Stem cells appear to hold the secret of regeneration. However, there are several different types of stem cells, each with different properties. What they have in common is two things: first, they can copy themselves by cell division; and second, some of those copied cells can turn into a wide variety of other types of cells - nerve cells, liver cells, lung cells, etc. A stem cell that is able to produce any type of cell in the body is called a "totipotent" stem cell. A stem cell whose copies can produce only a limited set of body cell types is called a "pluripotent" stem cell. Extending this definition, we might say that most cells of our bodies are "monopotent" - all they can produce is copies of their own cell type. From the point of regeneration, totipotent cells can do things that pluripotent cells cannot, while pluripotent cells are more versatile than monopotent or "normal" cells.

So far, no controversy. Now let us note another undeniable fact: the fertilized egg from which you, I, and everyone else in the world developed was a totipotent cell. It must have been, since it went on to produce every type of cell in our bodies. As the original fertilized egg that was going to become you began to divide, it passed through a stage where you looked like a little ball of cells. Many of those cells, particularly those in the middle of the ball, were close to totipotent. These are known as embryonic stem cells. As the original cluster of cells continues to divide, different cells begin to take on more specialized functions. They are going to become part of an eye, or a muscle, or a kidney, and they quickly pass from being totipotent to being pluripotent to being totally specialized as one particular cell type.

Now we can ask a very important question: Do any cells at all in the developing organism that is you remain totipotent, or even pluripotent? The answer is, yes - but.

If we define a stem cell only as a cell that can make copies of itself, some of which copies can be other types of cells, then we have these in our bodies. But here we come to controversy. There is general agreement that no adult stem cell can be totipotent, but no agreement at all as to the degree of pluripotency. Stem cells from the umbilical cord and from the placenta are candidates as pluripotent cells, as are stem cells from fatty tissue. However, few scientists believe that they offer the protean potential of embryonic stem cells to become all other cell types; and therefore, they argue, adult and umbilical stem cells do not offer the most promising route to the cell regeneration techniques needed to treat disease.

This would by itself be enough to cause intense arguments over the pros and cons of the use of embryonic stem cells. However, another and more controversial possibility lies just one step away. Suppose that you were to replace the nucleus of a fertilized egg with one of your own adult cells, and permitted the result to divide. It would form a little ball of cells, at the middle of which would be cells that are close to totipotent. If you want to place cells in your body for tissue regeneration, they are the perfect choice since they are actually your own cells. Your immune system will accept them, so there is no possibility of rejection or destruction as foreign tissue. This approach is known as "therapeutic cloning," and it adds to the stem cell debate all the suspicions of and aversion to the idea of cloning humans.

Where does all this lead? The stakes are incredibly high. How do we balance the quality of life and even life itself for existing people on the one hand, and on the other hand the rights of embryonic life - including possibly an embryonic form that if allowed to continue would become a copy of you?

I can't answer the questions of the previous paragraph. However, half a century of experience with drug use should tell us that if enough people want something badly enough, declaring it illegal will not work. Research into the use of stem cells may fall into that category. It will then continue elsewhere, perhaps in Europe where the laws on the use of embryonic stem cells are already different. And if the final results are anywhere near as good as some people believe they may be, this country will face an odd choice: either we reverse the policies that forbid treatment here, or we watch an increasing number of our sick citizens go abroad to seek medical help.

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