Bees do it, ants do it, and so apparently did the Goddess Athena. Parthenogenesis - Greek for "virgin birth" - could now allow British scientists to create human embryos from unfertilised eggs.
Athena was perhaps the first mythical character to undergo parthenogenesis, having emerged fully formed from the forehead of her father, Zeus. Hence her temple on the Acropolis is called The Parthenon.
Yesterday, Britain's fertility watchdog gave approval for scientists to create human embryos using a parthenogenetic process, in a landmark experiment that could pave the way for human cloning.
The Human Fertilisation and Embryology Authority (HFEA) granted a licence to the Roslin Institute, near Edinburgh, to use human eggs and embryos to generate embryonic stem cells which could be used to produce the specialised tissues of the body.
Professor Ian Wilmut, the scientist who cloned Dolly the sheep, will lead the Roslin team in its attempts to "activate" human eggs so that they develop into early embryos without first being fertilised by sperm cells.
The technique will in effect result in human embryos that cannot develop into fully mature and viable foetuses. The idea is to bypass many of the ethical concerns about experimenting with entities that could be considered potential human beings.
Harry Griffin, the acting director of the institute, said the licence would also allow the institute to culture immature egg cells from frozen ovarian tissue to boost the supply of fully mature human eggs.
The Roslin needs a large supply of eggs to carry out cloning by the Dolly technique, which will require a separate licence. "It helps us overcome a key limiting factor, which is the shortage of human eggs," Dr Griffin said.
A statement from the HFEA said that any stem cells created under the licence would be used for research purposes only, such as the possible testing of new medicines or the study of congenital diseases. Suzi Leather, who chairs the HFEA, said: "It is important that any research involving human embryos is scrutinised and properly regulated."
The licence allows the Roslin Institute to carry out research on "spare" embryos that have been donated by couples undergoing IVF treatment. It also allows the Roslin to experiment with unfertilised human eggs to create embryos by parthenogenesis.
Many species of animals, especially insects, use parthenogenesis as a form of natural reproduction. However, attempts at using artificial parthenogenesis in mammals have never been able to produce viable foetuses that developed normally.
Because of this, some American scientists do not even consider mammalian embryos made by parthenogenesis as embryos, preferring instead to call them "parthenotes". In 2001, the American biotechnology company Advanced Cell Technology (ACT) claimed to have produced early human embryos by parthenogenesis, but the research claims were subsequently criticised. But last year the same company announced the successful extraction of stem cells from monkey embryos created by parthenogenesis.
Robert Lanza, a member of the ACT team, said that the Roslin's licence to conduct similar research on human eggs would help in the understanding of cloning using the Dolly technique of replacing an egg cell's nucleus with the nucleus from another cell - so-called cell nuclear replacement.
"In the field of cloning, before you proceed with nuclear transfer of any species, you need to work out the activation protocol. That is learning how to fool the egg into thinking it is fertilised," Dr Lanza said.
But Christopher Barratt, professor of reproductive medicine at the University of Birmingham, dismissed the idea that the licence brought human therapeutic cloning by cell nuclear replacement closer. "It doesn't pave the way for cloning just because one aspect of their proposal involves the artificial activation of eggs so there is no transfer of a donor nucleus into a human egg," he said.
Professor Barratt, a member of the HFEA, said that the research was important because it could lead to the generation of human stem cells that could be used in transplant operations. "There are experiments on monkeys where parthenogenetic activation of eggs has developed stem cells and there is some evidence to suggest that these stem cells will develop into, for example, neurons [nerve cells]," he said.
Three other institutes in Britain have licences to extract stem cells from human embryos to research the possibility of using them to treat disorders such as Parkinson's disease, but the Roslin is the first to have a licence to generate human embryos by parthenogenesis.
In normal sexual reproduction, an egg or sperm loses half of its chromosomes so that when the two come together during fertilisation the full number is restored in the resulting embryo. In parthenogenesis, an unfertilised human egg is tricked into keeping the set of chromosomes that it would have otherwise lost. The result is an embryo that retains the full set of maternal DNA.
This year, it was reported that an American biotech company called Stemron had grown parthenogenetic human embryos. A spokeswoman for the HFEA said that the Roslin first got its parthenogenesis licence in June 2002, but only after an article in The Independent did the information became public. The HFEA denied that it was unduly secretive, saying it had a duty of confidentiality onlicence applications until they were granted.
Although it might be possible to extract stem cells from parthenogenetic embryos, their usefulness is questionable because they will consist entirely of maternal DNA. It would also be impossible to use this technique to generate a man's stem cells. A technique that could overcome this is cell nuclear replacement - or therapeutic cloning - where empty eggs cells are filled with a cell nucleus taken from the skin of a man or woman to generate a true embryonic clone.
The HFEA said it had not yet received a formal application to conduct that sort of research, but The Independent has learnt that at least one institute is in the final stages of negotiating criteria to apply for such a licence.
One scientist close to the authority said: "[Nuclear transfer is] moving at an incredibly rapid speed and I would envisage a number of applications for cell nuclear transfer coming along in the next few months."