In the Iliad, Homer described Chimera as “lion-fronted and snake behind, a goat in the middle, and snorting out the breath of the terrible flame of bright fire”. She was a monster, good only as a target for Bellerophon’s lead-tipped spear. To listen to the spiritual descendants of the Greek hero, you might think modern-day chimera were equally foul. The Catholic bishops leading the pro-life brigade don’t just want to destroy the monster, they want to ensure it never draws breath in the first place.
Yet the scientific meaning of chimera is far less fearsome. The word is used to describe creatures that have two or more different sets of genetic material caused when the zygotes of fraternal twins merge early in a pregnancy to form a single embryo. Test the DNA of, for example, the hair roots and saliva of a chimera and you would think they came from siblings.
But a person with this rare condition is no more a monster than you, I or even Cardinal Cormack Murphy O’Connor.
The Human Fertilisation and Embryology Bill, to which the Cardinal’s priests objected so vociferously over Easter, would allow the creation of three new types of human-animal embryos – chimerics, true hybrids and cytoplasmic hybrids (or cybrids), known collectively by the awkward term “human admixed embryos”.
Chimeras are made by merging the cells of animal and human embryos, hybrids by fertilising the egg of one species with sperm from another and cybrids by inserting human DNA into an animal egg from which the nucleus has been removed. Under the proposed new law, all three types would have to be destroyed after 14 days, and none could be implanted in a human womb.
The modern history of admixed embryos goes back at least as far as 1984, when sheep and goats were combined to create a geep. By 1990, hamster eggs were being used to check the fertility of human sperm. These true hybrids were allowed to grow for a day before being destroyed.
The first human-animal cybrids were made at the Shanghai Second Medical University in 2003 by fusing human cells with rabbit eggs. A year later, the Mayo Clinic in Minnesota announced it had created pigs whose veins carried human blood cells. And in 2005, British researchers added an extra, human, chromosome to mouse stem cells, leading to a strain of mice with Down’s syndrome, opening whole new dimensions of research.
The potential benefits of this sort of admixed embryonic research are so far reaching that many of them have not yet been imagined. Those that have been proposed include providing embryonic human stem cells (which are in short supply), animal models for research into human diseases and, perhaps one day, tissues and whole organs for transplant into humans.
Opponents of the Bill would have us believe that the DNA from humans is somehow different from the DNA of other animals, so they should not be mixed. In fact, at most levels, it is indistinguishable.
Deoxyribonucleic acid’s four bases – adenine, thymine, guanine, and cytosine – are found in the chromosomes of all life. The 20 amino acids used by life – each specified by a three-base codon in the genetic code – are similarly universal.
The proteins made up of amino acids are a bit more discriminating, but those found in humans are also present in a wide range of other animals. The difference is not in the fine structure, but in the way common components are assembled. Clearly, the division between human and animal is artificial.
With the potential medical benefits so great and the cell groups in question so microscopic, why is the pro-life movement so incensed? Perhaps it is because the real problem this presents to the religious right is not some unspecified “ethical question”; it is the risk of undermining the anti-abortion case. The idea that sacred human life begins with a single fertilised egg cell was clear and simple. It maintained the myth that we are superior to other forms of life, that we were created in His image. But should an embryo with 99 per cent human DNA get the same protection. Where now to draw the line?