Few breakthroughs in biotechnology have evoked such a mix of promise and paranoia as cloning has.

On the one hand, cloning could be a way to preserve endangered species or breed top-of-the-line livestock. But to many, the idea of cloning humans is an unsettling one.

To clone an organism, scientists remove the nucleus from a cell of one individual and transplant it into the egg cell of another individual that has had its nucleus removed. It's then moved to a uterus. When the egg matures, it holds the identical genes of the donor nucleus.

By the 1950s, scientists were able to clone frogs.

Mice were successfully cloned in the '80s.

But the real breakthrough came in 1997, when Scottish embryologist Ian Wilmut produced a lamb using DNA from an adult sheep's mammary gland.

Dolly the lamb raised the bar, because cloning a new animal from the cells of an adult rather than an embryo was thought by many to be impossible.

Dolly also raised a slew of ethical questions.

Should we be able to make carbon copies of ourselves in case we need an organ transplant?

Would these clones be our property?

Who would deliver them, and who would be their parents - or parent?

Could they be used to test new treatments for diseases?

Should we even try to clone humans?

As for that last one, researchers in South Korea say they already have - successfully.

Fertility specialists in that country say they created a genetic duplicate of a 30-year-old woman.

They also say they destroyed the embryo in the early stages of cell division because of unresolved ethical and legal questions.

Whether they actually did clone a human is up for debate. They haven't been very forthcoming with data.

But if they didn't, many say it's only a matter of time before someone else does.

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