After a human egg and sperm join in fertilization, an embryo begins to develop. By five days after conception, a hollow ball of cells has formed. The outer cell layer gives rise to the placenta. The inner 50 or so cells are known as pluripotent embryonic stem cells and go on to form the tissues of the developing embryo. Each of these embryonic stem cells can give rise to most cell types that make up an adult human body.

As the embryo continues to develop, its cells become increasingly differentiated. Most of them lose the capacity to develop into a wide range of cells. Instead they become specialized, functioning as a red blood cell, one of the cell types in bone, or whatever. However, even in adults some cells naturally retain a certain capacity to give rise to a variety of different cell types. For example, blood stem cells, located in bone marrow, can develop into red blood cells, platelets and the various sorts of white blood cells.

One way in which stem cells might be used is by what is generally referred to as therapeutic cloning. In therapeutic cloning a patient needing a transplant would have one of their ordinary cells removed-this could simply be a cell from the base of a hair or any other suitable tissue. This cell, or its nucleus, would then be fused with an egg cell from which the nucleus had been removed.

This resulting cell would then be stimulated to divide in the same way that the cell that gave rise to Dolly the cloned sheep was. If all went to plan, stem cells could then be isolated from this developing embryo and encouraged to develop into tissues. It is hoped that these tissues could then be used for transplantation. For example, a person with Parkinson's disease might receive a transplant of neural cells.

The principal ethical argument in favor of therapeutic human cloning is easily stated. It is that this technology stands a good chance of reducing human suffering and enhancing happiness. Indeed, it has been estimated that over one-third of the people in the United States are affected by diseases that may be helped by stem cell research (Perry, 2000). It may be that such benefits will be found to result from other technologies, for example through using stem cells derived from adults or from umbilical cords. However, most scientists believe that adult stem cells are likely to be less valuable for research and in developing new treatments than are the pluripotent stem cells that can only be derived from human embryos (e.g. Royal Society, 2000).

            In 2001 George Bush announced a ban on the creation of any new stem cell lines in the US. Following a personal consultation with the Vatican, and in response to public pressures to ban the use of human embryonic tissue in the manufacturing of cell lines, Bush's restrictions created a less favorable research environment in the US, where stem cell research is most advanced. Meanwhile, stem cell research in Europe has been strongly encouraged by the European Commission, leading some countries, most notably Germany, to liberalize their laws on embryo research to allow them to be used for making cell lines. According to the leading EC scientific research bulletin of 2001, 'Europe seems determined not to miss the stem cell train. The European Union already funds-to the sum of 27.4 million euro-15 research projects involving 117 laboratories in countries from Finland to Portugal' (European Commission, 2001, p. 7)…