A leading scientist has warned a new species of "humanzee," created from breeding apes with humans, could become a reality unless the government acts to stop scientists experimenting.
In an interview with The Scotsman, Dr Calum MacKellar, director of research at the Scottish Council on Human Bioethics, warned the controversial draft Human Fertilisation and Embryology Bill did not prevent human sperm being inseminated into animals.
He said if a female chimpanzee was inseminated with human sperm the two species would be closely enough related that a hybrid could be born.
He said scientists could possibly try to develop the new species to fill the demand for organ donors.
Leading scientists say there is no reason why the two species could not breed, although they question why anyone would want to try such a technique.
Other hybrid species already created include crossed tigers and lions and sheep and goats.
Dr MacKellar said he feared the consequences if scientists made a concerted effort to cross humans with chimpanzees. He said: "Nobody knows what they would get if they tried hard enough. The insemination of animals with human sperm should be prohibited.
"The Human Fertilisation and Embryo Bill prohibits the placement of animal sperm into a woman The reverse is not prohibited. It's not even mentioned. This should not be the case."
He said if the process was not banned, scientists would be "very likely" to try it, and it would be likely humans and chimps could successfully reproduce.
"If you put human sperm into a frog it would probably create an embryo, but it probably wouldn't go very far," he said.
"But if you do it with a non-human primate it's not beyond the realms of possibility that it could be born alive."
Dr MacKellar said the resulting creature could raise ethical dilemmas, such as whether it would be treated as human or animal, and what rights it would have.
"If it was never able to be self-aware or self-conscious it would probably be considered an animal," he said. "However, if there was a possibility of humanzees developing a conscience, you have a far more difficult dilemma on your hands."
He said fascination would be enough of a motive for scientists to try crossing the two species.
But he also said there was a small chance of scientists using the method to "humanise" organs for transplant into humans. "There's a desperate need for organs. One of the solutions that has been looked at is using animal organs, but because there's a very serious risk of rejection using animal organs in humans they are already trying to humanise these organs.
"If they could create these humanzees who are substantially human but are not considered as humans in law , we could have a large provision of organs."
He wrote to the Department of Health to ask that the gap in the draft legislation be addressed.
The department confirmed that the bill "does not cover the artificial insemination of an animal with human sperm".
It said: "Owing to the significant differences between human and animal genomes, they are incompatible and the development of a foetus or progeny is impossible.
"Therefore such activity would have no rational scientific justification, as there would be no measurable outcome."
Dr MacKellar disagrees. He said: "The chromosomal difference between a goat and a sheep is greater than between humans and chimpanzees."
Professor Bob Millar, director of the Medical Research Council Human Reproductive Sciences Unit, based in Edinburgh, agreed viable offspring would be possible. He said: "Donkeys can mate with horses and create infertile offspring; maybe that could happen with chimpanzees."
But he said he would oppose any such attempt. "It's unnecessary and ridiculous and no serious scientist would consider such a thing. Ethically, it's not appropriate.
"It's also completely impractical. Chimps would never be a source of organs for humans because of the viruses they carry and the low numbers."
Professor Hugh McLachlan, professor of applied philosophy at Glasgow Caledonian University's School of Law and Applied Sciences, said although the idea was "troublesome", he could see no ethical objections to the creation of humanzees.
"Any species came to be what it is now because of all sorts of interaction in the past," he said.
"If it turns out in the future there was fertilisation between a human animal and a non-human animal, it's an idea that is troublesome, but in terms of what particular ethical principle is breached it's not clear to me.
"I share their squeamishness and unease, but I'm not sure that unease can be expressed in terms of an ethical principle."
A Department of Health spokeswoman said: "It's just not a problem. If you inseminate an animal with human sperm, scientifically nothing happens. The species barriers are too great."