Wednesday, June 27, 2007

Clones, Chimeras and Cybrids Oh My!

This morning a really strange article caught my attention. The article alleges that the Catholic bishops of England have stated that Chimeric embryos created using human cells have a right to life and could be implanted in the genetic mother who supplied the human cells. The article quotes the Bishop's comments on draft legislation in England regulating stem cell research as saying:



“At the very least, embryos with a preponderance of human genes should be assumed to be embryonic human beings, and should be treated accordingly. ... In particular, it should not be a crime to transfer them, or other human embryos, to the body of the woman providing the ovum, in cases where a human ovum has been used to create them. ... Such a woman is the genetic mother, or partial mother, of the embryo; should she have a change of heart and wish to carry her child to term, she should not be prevented from doing so.”



What's going on here? First of all a chimera is essentially a genetic mosaic with cells from two different organisms. One might for instance take a mouse fetus and implant stem cells from a human in order to study the early development of cells in the nervous system. Chimeras seem odd but they may not be all that unusual. It is known for instance that some children are effectively chimeras, containing small numbers of cells from their mother. See this article from discover.



So a chimera is quite different from a clone, since a clone is genetically identical to its parent. Of course in nature, clones are produced via asexual reproduction. Now that may not be exciting to humans since we reproduces sexually but asexual reproduction is a normal part of the natural history of many organisms, plants as well as animals. "Identical" twins, more properly called monozygotic twins, in humans are clones.



Now there is a new new term- "cybrid." Cybrid, as used in biology, appears to be a contraction of cytoplasm + hybrid. Cybrids are often made by using the nucleus of one cell, say a human cell and injecting that nucleus into an enucleated cell from another individual-perhaps from another species. As pointed out here, the technique used to "clone" Dolly the Sheep Somatic Cell Nuclear Transfer, SCNT, results in a cybrid.



Isn't a cybrid a clone? Well, not really. That's largely because the cytoplasm contains mitochondria that have their own DNA. So Dolly had the nuclear genes from one the sheep that provided her nuclear DNA, but the mitochondrial DNA of the sheep that donated the egg cell's cytoplasm. A cybrid, by the way, is not a hybrid as biologists understand the term, since the term hybrid refers to an organism produced by breeding two genetically dissimilar organism.



Getting back to the Catholic Bishops, I was not able to find the original of the letter. They have not apparently soften their opposition to human producing animal chimeras, but believe that allowing the implantation of a chimera with a preponderance of human cells is the lesser of two evils-the other evil in their mind being the destruction of the embryo. This position is surprising to me because it goes way beyond the proposal in the Parliament. That proposal currently states that such embryos be destroyed by what would be the 14th day of development when implantation would be feasible.



To me the Bishop's position is not well thought out. First of all, how do they know that allowing a Chimera, even one supposedly mainly of human origin, is the lesser of two evils? Will society treat them as being fully human? Based on comments made on some sites, I suspect that many people might treat such chimeras as less than human.

For instance, consider this unedited comment from the Telegraph's web site:

"The Bischops of England, nor any other bischops have been granted such an authority to go beyond the current Church's teachings that, so far as I know are strictly forbidding in-vitro fertilizations. That's staggering: These innocent bischops are speaking about the mother's rights. OK fine. And what about those of the "father"? These Chimeras are an abomination: One day such monsters will be developped by mad scientists with the aim to overcome the human race created by God according to His plans, and destroy us either by their muscular strength or by their higher intelligence. The one question to ask the Church (not silly bischops) is: Have such human creatures a Soul? That I doubt since they have been created by men against God's laws."
If you subscribe to this sort of logic (and I don't dear reader), the conclusion is no soul-no rights. How can the Church Fathers seriously believe that allowing a chimera to be born is the lesser of two evils given that sort of reaction?

The Bishops may also have opened themselves up to a reconsideration of that basic Catholic doctrine: the soul.

"The unity of the soul and body is so profound that one has to consider the soul to be the 'form' of the body: i.e., it is because of its spiritual soul that the body made of matter becomes a living, human body; spirit and matter, in man are not two natures united, but rather their union forms a single creature." Catechism (365)


If chimeras that are mainly human have a soul then where is the cut off point when a chimera does not have a soul? How about a chimera produced from cells contributed by a human male? Would the Bishops allow that chimera to be carried by a surrogate mother to full term? Or is that one reproductive intervention too many for them? How about a chimera primarily originating from another mammal but with a relatively small number of human cells, say in the cerebral cortex, does that chimera have a soul? Gee...is the soul concept even useful?

To me, the Bishop's stance is not ethically defensible at this time. It leap frogs any sane proposal put forth by ethicists to handle the chimera situation. But flawed as it is, if the Bishop's proposal exposes the essentialist and typological thinking of the Church as indefensible, then maybe it has some value.

Other Links:

Could animal-human chimeras be on the way?

Chimeras on the Horizon


Embryos injected with human cells should be given human status. From Catholics online.
Post a Comment