Craig Venter, an American scientist and pioneer in thedrive to unravel the human genetic blueprint, said his project could help scientists to understand the fundamental nature of life and have practical benefits but acknowledged that there could also be malign uses of such a breakthrough, and that the experiment has serious ethical implications.
He told the American Association for the Advancement of Science (AAAS), in Los Angeles, that he had asked a body of religious leaders and ethicists to consider the moral implications of making a synthetic organism.
Dr Venter's plans are based on genes taken from Mycoplasma genitalia, a parasite which makes its home in human reproductive organs. It is the simplest life-form yet found, and is made up of just 470 genes, compared to the estimated 80,000 in human DNA. Research has established that just 300 of the microbe's genes are essential to its existence, although it is unclear what function 100 of these perform.
Now Dr Venter, head of Celera Genomics, wants to synthesise these 300 genes and get them to make their own self-reproducing cells. "We're trying to understand the minimum set of genes necessary to comprise a living cell," he said.
The idea drew a mixed reception from other scientists. "It is technically feasible, and it would be a daring piece of genetic engineering," said Steve Jones, professor of genetics at University College London. "The thing about nature, though, is that it has ways of being more complicated than we think."
Professor Richard Dawkins, author of The Selfish Gene, said: "Synthesising life in a test-tube would be a blow to the religious view that there's something special about life. But this is no different in concept from genetic modification of an existing life-form."
However, John Durant, professor of public understanding of science at Imperial College, London, said: "One can see potential benefits, but also potential risks. This work should be done in a very secure environment, like that for working with dangerous pathogens."
At the AAAS Frank Young, a former commissioner of the Food and Drug Administration who is now executive director of the Reform Theological Seminary, said: "The whole program of genetics has raised to the fore again a question that has not really been asked intensively since the Middle Ages - that is, what really is the essence of life? In today's terms, are we more than a collection of molecules?"
Dr Venter said, "We have not decided to go ahead and do the experiment yet. We are waiting for this ethical debate... But just because I wouldn't do it, it doesn't mean that somebody else would be so constrained. We think a public discussion of the issues is necessary because it gets down to the basic fundamental understanding of what the definition of life is. Right now we only make life from other living species," he said. He has passed on the details of his proposals to the American government's bioethics committee, seeking approval for the scheme.
The fine detail of the experiment is still being worked out. Dr Venter suggested that once his team had decided which genes to include in their synthetic life-form, its molecular blueprint could be fed into laboratory machines which will generate that DNA sequence in a test-tube. The result would be a gene sequence, or chromosome, that is "in effect, man made". That could be put into an existing microbial cell whose genetic material has been removed.
Practical benefits could include the creation of new medicines, or microbes that could clean up the environment, by tailoring their genes to requirements. But Dr Venter also acknowledged that such life-forms could be used to create biological weapons.
"The key issue is whether it is one of the slippery slopes that would lead to negative outcomes, such as bioterrorism. We do not want necessarily to create a recipe for creating worse pathogens than occur naturally," he said.