Human stem cell research and its possible connection to human cloning (i.e., somatic cell nuclear transfer) has been the subject of much debate recently. Significant confusion exists, however, in the public discourse on this topic--about what an embryo is, as well as about the ethical, religious, and legal issues involved. The aim of this essay is to clarify these issues and lay out as impartially as possible some of the ethical, religious, and scientific questions surrounding these complex matters, in the hope of stimulating and facilitating informed public debate.
Professor A.V. Hill in 1923, a future Nobel laureate, in an address to the Royal Philosophical Society of Glasgow, urged scientists to take a broad view. (1) He said:
The chief trouble I see with Science is that it is often not philosophical
enough; so many of its apostles cultivate some little corner of it so
intensively that they never find time or inclination to go up to the top of
the neighboring hill in order to see their own little patch in its proper
proportions, and to enjoy the romance of the larger landscape. (2)
I hope to outline in this essay some of this broader landscape--the ethical, scientific, religious, and public policy issues within which we need to think about human stem cell research.
Gametes--that is, ova and spermatozoa--carry one half of the genetic material, i.e., the DNA, of the female and male putative parents. When a spermatozoon enters an ovum and its DNA is introduced into the nucleus of the ovum, this DNA pairs up with the corresponding DNA already in the nucleus of the ovum, reconstituting its total genetic material in forty-six chromosomes. A fertilized ovum or zygote is thus formed. This can occur in the female genital tract (usually in the fallopian tube) as part of normal sexual reproduction, or in vitro fertilization (IVF) in the case of assisted fertility. In both instances the zygote starts to divide if conditions are favorable; first to form a blastomere of eight, then sixteen cells, and ultimately to form around day five a blastocyst. The blastocyst consists of 120 to 150 cells, some of which are the stem cells that can develop into all forms of normal human tissue. These are called totipotent. It is important to remember that at this stage the blastocyst, which is an early embryo, can divide into two or more living entities that can then develop into normal embryos. Thus, blastocysts are not individuals or unique entities. They are twinnable.
At fourteen days of development, a structure known as the primitive streak appears. This represents the primitive central nervous system. From this point on, the embryo is a unique individual and is no longer twinnable. As I shall discuss later, some authorities regard this developmental stage as critical in their thinking about when human, as contrasted to simply biological, life begins.
Finally, I wish to define the process of cloning. Based on the work of Ian Wilmut in producing Dolly the sheep, (3) this process involves removing the nucleus of an ovum and replacing it with the nucleus of an adult cell taken from the egg donor or another adult. This is known as somatic cell nuclear transfer (SCNT). This is a difficult task attended by a high failure rate. It took over 250 tries to get Dolly. (4) Using a fetal or embryonic cell as a nuclear donor is an easier way to achieve cloning. Such cloned cells are then induced to divide and develop into embryos.
SOURCES OF STEM CELLS
Totipotent stem cells can be obtained from blastocysts or other forms of early embryos. These are considered the most likely to be able to be grown into any organ of the human body or to be used for cell transplantation to help injured human tissues recover from injury.
Germ line cells from early fetuses, derived from terminated pregnancies, are almost as useful as embryonic stem cells. …