Would you rather have the heart of a pig or the face of a stranger? Neither, obviously. But what if you were dying and there were no human hearts available - would you take a chance on becoming the first person in the world to receive one from an animal and live?
Or what if your face had been burned away by fire? Some people are strong enough to cope with such a devastating experience, admirably, but what if you were not one of them? What if making children scream in the street turned you into a recluse and life seemed intolerable? Would you risk going under the knife then, for an operation that had never been done before in which someone else's facial skin was sewn on where yours used to be? Could you live with that?
These are questions most of us could barely begin to know how to answer. They are as alien to us as the dilemmas of science fiction. But they are matters of life and death to some people, right now. The news that a British team is seeking final ethical approval to go ahead with a full face transplant has seen medical science leap - once again - ahead of the limits of human understanding and experience. It feels like the final frontier of transplantation, breaking the last taboo - but may not be. There are other surgeons and scientists at work on replacing broken bits of the body. If swapping faces makes you feel queasy, how about giving birth from the same womb that carried you?
Six years ago, doctors in Saudi Arabia transplanted a womb to a 26-year-old woman but had to remove it after three months because she was close to dying through blood clots. The Swedish surgeon Mats Brannstrom carried out a similar operation in mice and announced that it could be done in humans "within three years". That was three years ago. "You could get the uterus from your mother," he said. "You could give birth to a baby from the uterus which you yourself were born from."
The possibility of using animal parts seemed to have faded before a leading British doctor declared last autumn that "clinical trials could take place within five years". Impossible, the sceptics said, not least because of the difficulty of stopping the body from fighting off invading cells from another species. But then there were many experts who said the face would fight off skin from a stranger - until the first partial transplant was carried out on the 38-year-old French factory worker Isabelle Dinoire in November. She was given a nose, lips and chin after being mauled by her own pet labrador. "I now have a face like everybody else," she said last month. "I will be able to live again." The drugs are working, for now, but the psychological impact remains unclear. Asked if she had really accepted her new face, she said: "It's too difficult to explain."
The drugs that all transplant patients must take to prevent rejection can also allow fatal cancers in. That is a risk worth taking if a faulty heart is going to kill you anyway - but the candidates for face transplants will have to be healthy, apart from their facial disfigurement, so why would they want to become sick patients with shortened lives? "One woman with severe facial disfigurement told me she would willingly trade a whole lifetime as she is for 10 years of normal life," says Peter Butler, the London-based surgeon hoping to become the first in the world to carry out a full-face transplant. "The typical story I hear from a patient is that he or she only goes out of the house once a week, wearing a scarf to cover their face. They go to the corner shop instead of the supermarket because fewer people will see them, they get their groceries as quickly as possible, visit the off-licence for alcohol then hurry home. And that is it. They don't open the door to anyone, even the postman. They live as a recluse. Is that living?"
Critics of the face transplant believe skin technology is providing less traumatic solutions, and that the publicity around it reinforces the idea that everyone with facial disfigurement hides away and feels suicidal. That is just not true. The Falklands War survivor Simon Weston lost his eyelids, lips and most of his nose in a blaze during the conflict, but has since written books and made many television appearances. He was initially opposed to the face transplant - and still says he does not want one for himself - but is now such a convert that he volunteered to put the case to the ethics committee of the Royal Free Hospital in north London last Wednesday. "Those who cannot come to terms with their deformity should have the opportunity of receiving one," he had written. "Denying them the chance of a new face would be to imprison some people in a life they cannot tolerate."
Every leap forward in transplantation has been considered shocking in its time. Dr Christiaan Barnard was accused of playing with life for the sake of glory when he carried out the world's first heart transplant in Cape Town, South Africa, in 1967 - particularly when the 55-year-old patient died after 18 days. The operation is still very dangerous - one in five patients does not survive the first year - but not unusual: 262 people in Britain have received second-hand hearts in the past year.
Attaching a dead hand to a living man felt weird when it was done in France in 1998, but the same thing has since been done two dozen times. Most worked better than the first: Clint Hallam, a 45-year-old New Zealander, felt revulsion towards the new hand from the start but couldn't tell anyone. "At the news conference after the operation there were nine doctors sitting with me," he said later. "What could I say? 'I hate the hand?'" He stopped taking his medicine instead, 15 months after the operation, and the limb started to die as it was rejected by his body. In the end Mr Hallam asked the surgeons to remove it. "My advice to anyone contemplating this kind of surgery would be to run away."
Doctors say they have learned to select more suitable patients. Transplants have almost become a normal part of life, but there are still signs of squeamishness. Nine out of 10 British people say they support the idea of donating organs or body tissue, but only two in 10 actually sign up to be on the register, which currently contains around 13 million names. Most of these are happy to donate any organs or tissue at all but 10 per cent tick a box to say they want to make an exception - usually for the eyes.
"So few of us will die in the right circumstances to be donors," says John Oliver of the co-ordinating body UK Transplant. You usually have to be on a ventilator in an intensive care unit so that your organs can be "harvested" and maintained properly before use. Last year, 765 people were donors after death, making 2,196 transplants possible. There are said to be five times more potential patients than organs, however. In Britain at the moment 6,700 people are waiting for body parts to become available.
Animal organs were long thought to be the best hope of solving the shortage. Xenotransplantation would provide a vast and instantly available army of potential donors, with pigs the favoured candidates. We already rear and kill them for food, so why not? Because many people find the notion impossible to accept on religious or moral grounds, for one thing. And there are substantial scientific problems.
The first is rejection, during which antibodies in human blood attack sugar on the surface of pig cells. Scientists have used genetic modification to rear pigs that do not produce this sugar, meaning they might be able to beat the human immune system. It is not just hearts they could provide. Cells from the pancreas of a newborn pig have been transplanted to the body of a rhesus macaque monkey with diabetes and produced insulin that kept it healthy for almost a year. The team at the University of Alberta in Canada now wants to do the same for diabetic humans.
The second major problem with xenotransplantation is that pigs have viruses written into their genetic code and nobody knows what harm they might cause in humans.
However, Dr Anthony Warrens, of Imperial College in London, surprised many people when he told the British Association science festival last autumn that the threat was receding as science advanced. Human trials may be possible within five years, he insisted. "Although we can't say there is absolutely no danger of cross-infection, I believe that in the future we will be able to deal with many of the problems."
Animal transplants are banned in Britain, for now. Anyone who wants to carry out human trials has to apply to the Xenotransplantation Interim Regulatory Authority set up by the Government. Three years ago its experts said that if a new virus mutated the NHS would face massive compensation claims. Bioscience companies that were energetically fusing pig hearts with baboon necks became less keen.
They are now concentrating on growing healthy body parts from stem cells. Earlier this year it was announced that seven patients in North Carolina had been given bladders grown from their own cells.
Pig hearts may still be viable if they can be grown to contain human genes. But guinea pigs are more important. Whatever surgeons want to do, they ultimately need patients. The corporations may dream of giving young faces to the old or making fading bodies beautiful, but for now pioneering transplant surgery is far too dangerous. Those who volunteer for it must feel they have nothing to lose. That is not unusual in transplant patients - although few can have been in more desperate situations than David and James Morrison. The father and son from Birmingham suffered from the same rare disease and were side by side in hospital beds in September waiting for hearts. Mr Morrison told the surgeons to "forget about me and sort out James", but it was not as simple as that. He got his heart operation, but there was no match for James, who caught pneumonia. Hours after finding out that his dad was OK, James died in the arms of his mother Sue. If she or Mr Morrison had been offered anything - human or otherwise - that might have saved him at that moment, they surely would have taken the risks.
Many transplant surgeons can offer stories just as moving. They would insist that while the offers we started with may be hard to accept if you are happy and healthy, there are plenty of people in darkened rooms and hospital wards ready to answer, 'Yes, please.'
What they can transplant (and what they hope to)
First recorded transplant of transparent surface of the eye in Moravia (now part of the Czech Republic) in 1905; there were 2,503 in the UK last year.
First patient was Isabelle Dinoire, 38. Received nose, lips and chin of a donor in France last November. British surgeons are now seeking final ethical approval for the first full facial transplant.
First human heart transplant by Dr Christiaan Barnard in South Africa in 1967: 262 in UK last year, some with lungs.
First transplanted at Stanford University in the US in 1981. Reasons include cystic fibrosis and emphysema. In the UK, 150 carried out last year, some with heart.
First used as a temporary measure in 1881. Grafts provide protective dressings or reconstructions after severe burns: 500 recipients in UK every year, half of whom are children.
First performed in Boston, US, in 1954. Of 1,799 in UK last year, 594 were donated by a living friend or relative
First procedure in Ontario, Canada, in 1988. Also known as the small intestine, it is 22ft long and is where nutrients from food are absorbed.
First transplanted in Denver, in the US, in 1963. Last year, 586 in the UK, but a chronic shortage of donors.
First transplant in Minneapolis, in the US, in 1966. Helps patients with type 1 diabetes: 126 in the UK last year, often with kidneys.
First transplanted in Belgium in 2003. Removed from a young woman about to have chemotherapy, frozen and reimplanted seven years afterwards. She later gave birth.
Promised within three years by a Swedish scientist, who said best donor would be the patient's own mother. That was three years ago, but is yet to happen.
First transplant was in France in 1998. Patient Clint Hallam, 45, later asked for the hand to be removed. Since then, 24 around the world.
First attempt at a hand transplant, in 1964, was unsuccessful, but individual tendons could be transplanted. Now often used to heal sporting injuries.
First recorded success was with bone of a dog in 1688. Human thigh-bone graft can prevent amputation in patients with bone cancer. Also used after injuries.
Veins & arteries
First used in reconstruction in 1911. Vein from a donor's leg can be wrapped around nerve in the wrist to prevent repetitive strain injury.
British scientists hope to cure crippling osteoarthritis within a decade using transplanted cartilage grown from stem cells.
Human trials may begin within five years, according to British scientists. Pigs are being genetically modified to include human cells.Reuse content