Life does not begin when sperm meets egg, but 14 days after, according to the head of the Anglican Church in Australia.
Primate Peter Carnley told the Fertility Society of Australia in Perth yesterday this meant objections to IVF, genetic testing and stem cell research should fall away.
Archbishop Carnley said that until it was implanted in a womb lining, a fertilised egg was not a human life but rather a genetically novel kind of cell.
The fertilised egg must also pass the point that it could split to become an identical twin, which was at about 14 days. After that, the embryo should be accorded the status of an individual human with rights to care, protection and life.
Dr Carnley's position clearly contradicts that of the Catholic Church, which holds that life begins when an egg is fertilised.
But Dr Carnley said the debate about the beginning of life within the Christian faith did not come to that view until 1869, when Pius IX declared all abortion was wrong from the beginning of conception.
Dr Carnley argued that scientific knowledge had moved forward since then and must be taken into account.
If conception was defined as the meeting of gametes - egg and sperm - then the cloned sheep Dolly was not conceived, because Dolly was the product of cell nuclear transfer, where the ovum nucleus was replaced by DNA from an adult cell.
"I think it is now clear that we must begin to think of conception less as a moment and more in gradual and continuous terms as a process," Dr Carnley said.
He said since 1984 Anglican moral theology had concluded that conception was a 14-day process and this helped shape legislation around the world.
"Given that twinning can occur up to the 14th day of this process, it is not logically possible to talk of the conception of a unique human individual prior to the completion of this process.
"Each of us can say that we came to be in the sense that we were each conceived, as a potential human individual, 14 days after the fertilisation of an ovum, not before." He said the natural 60 per cent wastage of ova during IVF procedures need not be considered the killing of conceived human individuals.
"We do not have some 70,000 frozen people on ice at various places around Australia," he said.
Embryo experimentation and stem cell research were also morally acceptable.
"If there is a utilitarian argument for the possible benefit to mankind of experimentation on embryos, this could be tolerated in a controlled way under licence up until the 14th day in a way that after the 14th day it would not," he said.
"Stem cell research becomes also thinkable, for stem cells are harvested well within the 14th day period."