Next month a report from a committee chaired by Ian Kennedy, professor of medical law and ethics at King's College, London, will recommend that xenotransplants should be permitted; that pigs' organs - the animals' hearts and kidneys - can be surgically placed inside human beings.
The Nuffield Council on Bioethics made the same recommendation earlier this year. The Government, however, has chosen to leak the Kennedy report to indicate that ministers were giving some consideration to the possibility that xenotransplants might allow retroviruses to cross from pigs to people. These viruses cause few problems to their natural hosts, but can cause havoc when they cross from one species to another. HIV, the retrovirus which can lead to Aids, is often assumed to have crossed to humans from a species of monkey.
The ideal animal to supply organs to humans would be the chimpanzee, whose DNA differs from ours by less than 2 per cent. But the Nuffield committee suggested that, on ethical grounds, we could not use apes and monkeys for transplant, because primates are too close to humankind. Yet such moral scruples, they concluded, need not apply to pigs.
A similar issue was raised over genetically engineered maize and soya. Perfectly safe, say the scientists employed by the American firms which make them. And many of those without vested interests agree: John Habgood, the scientist, theologian and former Archbishop of York, once told me that he would happily eat a chop from a lamb which had been engineered to include a human gene - for what difference could one gene make among so many millions of lamb genes?
Yet many of us remain uneasy. We may become more so as our pluralistic society makes it even more difficult to make judgements about about what is, in fact, natural. And how can we reach a consensus when our society has no common moral language? An increasing number of cases over the past 12 months have thrown this dilemma into relief.
At the start of the year, the parents of a brain-damaged child applied to the High Court for permission to withdraw his food, and so allow him to die. At the end of the year we have concerns over animal organ transplants. In between, some 3,000 frozen embryos were destroyed; a woman had one of her two twins aborted; and another refused the selective abortion which doctors recommended when she conceived octuplets while on fertility treatment. A third unsuccessfully demanded the right to have a posthumous baby using the sperm of her dead husband. And then a 51-year-old grandmother gave birth to her wombless daughter's baby.
The questions which such cases aroused generated more heat than light. And yet they ought to have been simple enough to formulate. Is it safe? Is it natural? Is it legal? Is it kind? Is it right? And do we have to answer "Yes" to all of those questions before we proceed in such cases?
Some of the cases did not present new issues so much as dramatise old ones in a new way. The case of the woman who wanted rid of one of her twins was significant because it made many of those who back the "pro- choice" position feel uneasy. It confronted them with the essential arbitrariness of abortion, particularly so when it was disclosed that the woman concerned was a middle-class, high-income wife. What had been presented as a poverty issue was exposed as a convenience one.
Other cases presented new moral dilemmas.
The expiry of the deadline for the storage of Britain's first frozen embryos faced us with the consequences of a decision made five years ago. There were echoes of the abortion debate in all this: this was human life, but were they human beings?
The new underlying ethical issue of ownership was largely neglected. And without such a discussion we may yet face rows over the ownership of genetic material - for example, in the case of the woman in the US who recently conceived and then aborted in order to produce foetal material for use in the treatment of her father's Alzheimer's disease.
We are increasingly looking to science as a device to delay the need to face up to the metaphysical issues at the heart of mortality and infertility alike.
And all this is set in the context of National Health Service reforms where the internal market has strengthened in the public mind the link between medicine and money, at the expense of a link with morals. Combine that with the growth of our "rights" culture - in which all unfulfilled desires seem to be seen as an abuse of human rights - and you get the test-tube pioneer Lord Winston trying to have the law changed to allow Diane Blood to be impregnated with sperm taken from her dying husband.
Traditional British prejudices cloud the issue here. The sympathy quotient for Mrs Blood was boosted by the "one-of-us" factor. She was an articulate middle-class advertising executive. Contrast that with the case of Mandy Allwood who conceived octuplets while on fertility treatment. The controversy surrounding her refusal to undergo the selective abortions her doctors recommended, and the subsequent death of all the foetuses, was reinforced by her deal with the publicist Max Clifford and the News of the World.
Ms Allwood was widely deemed an unsuitable candidate for fertility treatment in the first place - she had had a child already, and an abortion, was not in a stable relationship, did not tell her partner she was having the treatment, and had sex when doctors told her not to. Such a judgement operated entirely on unstated assumptions about how society should decide who should get fertility treatment.
Unstated assumptions and inconsistencies bedevil the entire bioethics debate. One of the most alarming examples lies in the developments oneuthanasia this year.
The parents of two-year-old Thomas Creedon edged into new territory when they decided to go to the High Court to ask for permission to stop feeding their brain-damaged son. Another, anonymous, couple went further, beginning proceedings to be allowed to administer a lethal injection to their brain-damaged baby whom doctors predicted would die in infancy.
Thomas Creedon died before his case came to court; the other case has yet to be heard. But what the slippage reveals are some unchallenged assumptions about what constitutes a "worthwhile" life.
In Britain there are hospitals where - although officials will not publicly acknowledge this - it is impossible for those aged over 70 to get treatment.
Perhaps society might be happy to endorse such assumptions. But it is dangerous when they go unarticulated and are therefore never subjected to public challenge.
But choice cannot be all. We have some important moral intuitions about not killing people, about the sacredness of life, about not messing with nature, about our inter-relatedness, and our responsibility for one another. If these intuitions were not inherent in our make up, then what is possible and permissible could slide into what is expected or even inevitable.
The danger is that in leaving such decisions to the individual some important human values may be undermined.
In the case of the surrogate grandmother, we may ask what harm can it do when all are happy? But there are other questions. How would the daughter have felt if her 51-year-old mother had died during the pregnancy? How would they cope if the childwere handicapped? Or later abused? What would have happened if a pre-natal scan showed abnormality and the mother wanted to abort but the grandmother disagreed?
Just because nothing went wrong this time is no answer. Moral responsibility requires us to think beyond the immediate.
The argument against surrogacy is that it makes women vulnerable - poor women to economic exploitation and grandmothers, now, to emotional manipulation. To warn thus is not to adopt a Luddite position. The risk analysis which the scientists have done on xenotransplantation may indicate that the benefits greatly outweigh the possible harm. Most of us would be content to take expert advice on such matters. But it has to be advice; we have to be given the choice on whether we want to eat genetically altered maize. Most importantly that choice has to be an informed one. If it is not we may have to pass that choice to a higher authority.