Dolly, the world's most famous clone

Human cloning is perhaps the most controversial reproductive technology, raising fears in people's minds of armies of clones or exact copies of people long dead.

But most scientists working in human cloning are not concerned with making babies, but with creating stem cells that can be used to treat genetic diseases.

In February 2004, South Korean scientists became the first to clone human embryos, creating 30 early-stage embryos from more than 200 eggs.

The Seoul scientists harvested a colony of stem cells from one of the embryos they created. They credited their success to acquiring very fresh eggs from volunteers and to gentle handling of the genetic material inside the cells to be cloned.

They said their goal is to grow replacement tissue for patients with genetic diseases, such as diabetes and Parkinson's disease, from their own cells so that their bodies are less likely to reject the tissue.

The announcement followed a series of earlier cloning experiments by other researchers.

On December 27, 2002, Clonaid, the self-proclaimed "first human cloning company," said they had successfully cloned a human baby girl, although their claims were met with considerable skepticism.

The Raelians, a religious sect that believes life on Earth was created by extraterrestrials, established Clonaid in 1997.

Brigitte Boisselier, a chemist and the CEO of Clonaid, said the girl, named Eve, was "very healthy" and is the clone of a 31-year-old American woman, who resorted to cloning because her husband is infertile.

But Boisselier didn't offer DNA evidence to verify whether the baby girl is a clone.

Cloning experts were skeptical about the claim, saying cloning a human is technically demanding and the group lacks the skills to do it.

In November 2001, an American company announced it had cloned the first human embryo using the same technique that produced Dolly the sheep back in 1996.

The private company, Advanced Cell Technologies, hopes to use the procedure to isolate stem cells and help patients with a wide range of medical problems. Stem cells are cells that haven't matured to perform specialized functions, which means they still can be programmed to do anything.

The human embryo cloning experiments failed to produce therapeutic stem cells because the embryos did not divide enough times. Theoretically, the cloned embryos could provide a perfect match for a patient and prevent rejection problems.

Unlike the Raelians, most scientists do not intend to use these technologies to clone humans. Some, however, are considering cloning humans for reproductive purposes. In March 2001, three scientists gathered in Rome said they're going ahead with human cloning, no matter what anyone says.

They said their intention is to help infertile couples to have children.

"Some people say we are going to clone the world, but this isn't true," Italian Severino Antinori, one of the doctors, said at a news conference. "We're talking science, we're not here to create a fuss."

The team plans to combine cells (from either the man or the woman) with one of the woman's eggs, which has been stripped of its genetic material. When the cells form an embryo, the scientists would implant the embryo in the woman's uterus. The embryo would then take its "natural" course and develop into a fetus and then a baby – a baby that would have only one biological parent.

The Raelians say they used a similar technique to create Eve.

The idea that we may one day clone a human being has been a part of science fiction and scientific debate for generations.

However, it wasn't until 1997, when a team in Scotland announced it had cloned the first adult mammal, the now-famous Dolly the sheep, that the world really changed the way it thought about human cloning. Those who were previously asking whether it could be done were now asking when it would be done.

But there's still the question of whether it should be done. And the ethical issues that surround human cloning can be as complicated as the science itself.

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