The idea of cloning animals was first suggested in 1938 by a German embryologist called Hans Spemann. He proposed what he called a "fantastical experiment" to remove the nucleus from an egg cell and replace it with a nucleus from another cell.

14 years later in 1952, two American scientists, Robert Briggs and Thomas King attempted this. They used very fine pipettes to suck the nucleus from a frog egg and transfer a nucleus sucked from a body cell of an adult frog into its place. The experiment failed when conducted in this way. However, partial success was achieved in 1970 when British developmental biologist, John Gurdon, inserted nuclei from advanced frog embryos rather than adult tissue. The frog eggs developed into tadpoles, but died before becoming adults.

In 1980, the U.S. Supreme Court ruled that live, human-made micro-organisms were patentable material, paving the way to make cloning research profitable. Technology continued to advance and in 1984 Steen Willadsen, a Danish embryologist working in Texas, succeeded in cloning a sheep using a nucleus from a cell of an early embryo. This exciting result was soon replicated by others in a host of other organisms, but it only seemed to work when early embryo cells were used. Researchers began to think that animal embryo cells became irreversibly "committed" after the first few cell divisions and that nuclei from differentiated animal cells could not be used to clone entire organisms.

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However, as knowledge of the cell cycle advanced, it became apparent that cells don't divide until conditions are appropriate. Keith Campbell, a geneticist in Scotland reasoned that the egg and the donated nucleus might need to be at the same stage in the cell cycle. In 1995 he and reproductive biologist, Ian Wilmut, succeeded in cloning farm animals from advanced embryos. They then went on to clone an adult mammal for the first time, producing a lamb named "Dolly" from a six-year-old ewe, using tissue taken from the ewe’s udder. She was the only one of 277 nuclear transfers to make it into the world.

In 1997, Wilmut and Campbell created Polly, the first sheep with a human gene in every cell of its body, meanwhile President Bill Clinton banned the use of federal funds for cloning research for five years. Since then scientists have successfully cloned a host of animals, including mice, cattle, goats, and pigs.

Fears of reproductive cloning in the future were raised in 1998 when Richard Seed, a Chicago scientist, announced that he would attempt human cloning in the future. Also in 1998, Bonnie, a natural offspring of Dolly, was born, proving that Dolly is able to breed normally and produce a healthy baby. Britain later went on to issue a patent to Geron Corp. for the cloning process that created Dolly.

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In 2001, Britain's House of Lords effectively legalised the creation of cloned human embryos for stem cell research purposes, with the prerequisite that the cloned embryos are destroyed within 14 days. Later in 2001, a Massachusetts research company, Advanced Cloning Technology (ACT), reported that it had cloned the first human embryo, a development it said was aimed at producing genetically matched replacement cells for patients with a wide range of diseases. The success of this was limited, however, while only one of the embryos reached the six-cell stage, all of the company's cloned embryos stopped developing after only a few hours.

The most recent development in the cloning story happened on 27th February 2002 with the House of Lords’ announcement that stem cell research is now legal. This is for therapeutic cloning only, so reproductive cloning is still banned. However, this move still brings fears that it could be the start of a 'slippery slope' towards reproductive cloning with identical copies of human beings, being created.

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