Last week, Britain made a landmark decision that allows researchers to use animal eggs in the creation of human stem cells.
The ruling, laid down by the Human Fertilization and Embryology Authority, makes Britain the first country in the world to explicitly enable scientists to use human-animal hybrid embryos for research.
Hybrid embryos are banned in the United States, Australia, and Canada. Several countries in Europe, meanwhile, either allow scientists to only work on pre-existing embryos, or ban embryo research, altogether.
In an interview with ABC News, a spokeswoman from the HFEA said that the organization had carried out a detailed consultation with the public before its ruling.
"We found that, once people understood the science behind hybrid embryos, they changed their views," she said.
The Science Behind the New Embryos
The plan involves taking an animal egg, usually from a cow or a rabbit, removing most of its own DNA content, and injecting human DNA into the empty animal egg. The resulting egg would then contain 13 animal genes compared with 20,000 to 25,000 human genes.
After scientists use a tiny jolt of electricity to encourage the egg to divide, it becomes an embryo in its earliest stages.
It is from such embryos that British scientists plan to extract stem cells — cells capable of developing into any human tissue.
Experts argue that using animal eggs filled with human DNA taken from a person suffering from a disease like Alzheimer's, for example, would allow them to study the resulting stem cells to see how the disease develops.
At present, researchers rely on a limited stock of human eggs left over from in vitro fertilization treatment. The HFEA ruling is expected to make it easier for scientists to conduct their research, without being dependent on a scarce supply of eggs.
Currently, two teams, from King's College London and Newcastle University, have applications pending with the HFEA, which has said that permission to develop hybrid embryos will be decided on a case-by-case basis.
Stephen Minger, leader of the King's College team, told ABC News that the HFEA ruling was "very good news for scientific research."
"We don't have thousands of young women coming into labs with embryos that we can use for research," he said, explaining why the new regulation was necessary.
If their proposal is approved, Minger's team intends to use the hybrid embryos to study the development of Alzheimer's, Parkinson's, and spinal muscular atrophy.
Their plan is to inject DNA, from patients suffering from these diseases, into empty animal eggs until they divide and form embryos. The resulting embryos will hold the patients' DNA, and enable Minger's team to understand the progression of the diseases.
Opponents and Critics Weigh In
As expected, the UK-based Alzheimer's Research Trust, and the Motor Neurone Disease Association, have welcomed the news of the HFEA ruling.
Rebecca Wood, chief executive of the Alzheimer's Research Trust, told ABC News that "stem cell research is an important part of Alzheimer's research."
Alluding to the "yuck factor" associated with the notion of human-animal hybrids in many people's minds, Wood insisted that such feelings "should not overrule the possibility of finding something" that may help evolve better treatments for Alzheimer's patients.
Belinda Cupid of the MND Association released a statement saying that "the case for the use of human/animal hybrid embryos in stem cell research, is compelling, as it holds the potential to save lives."
But, critics of the ruling say that it disrespects the sanctity of human life, by blurring the distinction between species, and by producing embryos expressly for research purposes.
Currently, all hybrid embryos produced under the HFEA regulation must be destroyed after 14 days.
Anthony Ozimic, secretary of pro-life group the Society for the Protection of Unborn Children, insisted that "human life begins at fertilization. So, the creation of an embryo must be treated as a human life.
"Experiments such as the ones scientists plan to carry out will destroy the embryo.
"Furthermore," Ozimic said, "SPUC has an intrinsic opposition to the creation of hybrid embryos, because it's against human dignity. ... There's a reason that species don't mix like that."
His views are echoed by Josephine Quintavalle, director of Comment on Reproductive Ethics. "This notion of embryos crossing over the species barrier is very offensive to the integrity of both species.
"This is not just about a transplant," she added, adding that "it's about making a whole new kind of entity."
"You Cannot Take One Life to Save Another"
Although opponents like Ozimic and Quintavalle raise visions of mutant creatures roaming the streets of London some day, if hybrid embryos fall into the hands of a rogue physician, practicing scientists like Minger dismiss such notions as "nonsensical. ... As far as I am concerned," he said, "these embryos are intended for lab research only.
"You cannot implant them under existing laws," Minger said. "They will be destroyed two weeks after they are created."
But, this provides no comfort for right-to-life advocates like Quintavalle, who remained adamant in her insistence that "you cannot take one life to save another."
To Minger, however, such moral objections are unreasonable, noting that "hundreds of thousands of embryos are destroyed in the IVF process every year.
"People who criticize what we are trying to do don't understand what we're doing," he said.
"Or," he added, "they choose not to listen."
Tony Calland, chairman of the British Medical Association's ethics committee agreed. "Some members of the public hold bizarre, unrealistic, and unreasonable views," he said. "They take on a purist, fundamentalist stance, opposing any kind of embryonic research."
In fact, until recently, opposition to such research even extended to the British government, which, under former Prime Minister Tony Blair, had considered banning the creation of hybrid embryos.
But, this year, the government took a step back and reversed its decision, after protests from the scientific community and patient groups.
Now, in addition to the teams from King's College London and Newcastle University, the Institute of Psychiatry in London, and Queen's Medical Research Institute at the University of Edinburgh, are also expected to apply to use hybrid embryos for research.
Minger's team anticipates a decision this November.
If the outcome of his application is positive — as is widely expected — the number of researchers applying for similar permits promises to grow.
As for the moral objections to such research, Wood acknowledged that "ethics always need to be carefully considered."
But, she added, "we work with Alzheimer's patients and their families constantly, and we see the reality on the ground. And we feel that hybrid embryos need to be considered, no matter how controversial."
ABC News' Dan Childs contributed to this story.