The formation of these hybrids is a relatively recent phenomenon with some scientists say the more humanlike the animal, the better research model for testing drugs or possibly growing "spare parts," such as livers, to transplant into humans.
Watching how human cells mature and interact in a living creature may also lead to the discoveries of new medical treatments.
However, the moral implications about the creation of animal-human mixtures, especially at the embryonic and foetal level are deep as the creation of animals with certain kinds of human characteristics or with human brain and reproductive cells, would be offensive and unnatural.
The report, published by the Scottish Council on Human Bioethics (SCHB) was written in the light of new draft legislation on human embryology being prepared by the UK Department of Health (which is to be published during the course of summer 2006).
The report lists a series of 15 recommendations designed to allay concerns to whether or not chimeras would be used for procedures that are problematic or risky.
The recommendations state that:
- The creation of an embryo containing cells made up of both human and animal chromosomes should be prohibited.
- The insertion of a human cell nucleus or chromosomes into a non-human egg stripped of its chromosomes enabling an embryo to exist should be prohibited.
- The mixing of animal and human gametes should be prohibited.
"The fertilisation of animal eggs with human sperm should not continue to be legal in the UK for research purposes," said Calum MacKellar, director of research of the SCHB.
"Most people are not aware that these kinds of experiments have been taking place in the UK and find it deeply offensive; parliament should follow France and Germany and prohibit the creation of animal-human hybrid embryos."
The SCHB is also calling on government not to use animal eggs to create cloned animal-human embryos in order to address the serious shortage of human eggs that are available. This procedure is currently unregulated by legislation in the UK.
The potential power of embryonic and foetal inter-species mixtures became clear about a decade ago in a series of dramatic experiments on chickens and quails. The resulting offered astonishing proof that complex behaviours could be transferred across species.