Report on Human Cloning through Embryo Splitting: An Amber Light
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The prospect of human cloning has reemerged as a frontier bioethical issue. In 1993, investigators reported that they had successfully formed multiple embryos from single human embryos, as had been done previously in animals (Hall et al. 1993). From 17 very early embryos, 48 blastomeres—or theoretically 48 new totipotent embryos—were obtained. The embryos used were abnormal, however, and could not implant. A major purpose of this research was to enhance the chances of pregnancy in infertile couples by increasing the number of embryos available for transfer into the womb. While some commentators found no serious problems in proceeding with research of this sort, others speculated about the negative ethical and social implications of producing multiple copies of genetically identical humans.
Cloning has several different meanings in the biological sciences. In general, it refers to artificially induced asexual reproduction that produces beings genetically identical to the original from which they are cloned. Two quite different laboratory procedures aimed at duplicating embryos have been termed cloning: embryo splitting and nuclear transplantation.
Embryo splitting, also known as blastomere separation, involves isolating individual cells or clusters of cells of very early embryos and growing them into separate embryos. Cells at this stage are totipotent, which means that they have not begun to differentiate into specific tissues, such as bone or muscle, but carry their full genetic complement for development. Each separate cloned embryo, therefore, has the same genetic make-up as the original. The number of viable human embryos that can be produced by blastomere separation of a single embryo ranges up to four (J. Cohen 1994). This procedure has been used successfully to increase the pregnancy rate of cattle (J. Cohen 1994), but no reports of its use in normal human cells have been presented in the literature.
The second procedure, nuclear transplantation, involves taking the cell of an animal or human, removing the nucleus, and introducing it into an unfertilized egg from which the nucleus has been removed. The donor nucleus then controls the development of the egg, which, once implanted and brought to term, results [End Page 251] in a being genetically identical to the original. Although the microtransfer of donor nuclei from embryos has resulted in successful cloning in cattle and other species, there has been no nuclear cloning in the mammal using nuclei that have developed beyond the embryonic stage (Jones 1994).
Some major differences between embryo splitting and nuclear transplantation include: (1) embryo splitting requires two progenitors, whereas nuclear transplantation from an adult requires only one; (2) embryo splitting produces only limited numbers of duplicates of the original, whereas nuclear transplantation, in theory, allows large numbers of duplicates of the original; and (3) embryo splitting does not entail direct manipulation of genetic material, whereas nuclear transplantation does.
The possibility of human cloning and the questions it raises are as old as the field of bioethics itself and have been debated by such pioneer bioethicists as Paul Ramsey (1970a) and Joseph Fletcher (1971). The issue, however, has not been given much serious consideration since the late 1970s, when cloning by nuclear transplantation was the topic of the day. A book published at that time, In His Image: The Cloning of a Man by David Rorvik, stirred intense, albeit short-lived, attention. Rorvik claimed that a 62-year-old, wealthy businessman had been successfully cloned through nuclear transplantation. The possibility of cloning human beings raised concerns at that time that revolved around three sets of questions: (1) Why would anyone want to clone humans?; (2) Will cloning fundamentally injure our perception of what it means to be human and will it negatively affect individual identity and uniqueness?; and (3) Will the anticipated biological and social effects of cloning have a beneficial or detrimental effect on our underlying ethical framework and social fabric?
A 1978 congressional hearing elicited a general consensus from prominent biologists that cloning in the fashion described by Rorvik was not technically feasible, nor was it desirable or necessary (Subcommittee on Health and the Environment 1978). Even in Splicing Life: The Social and Ethical Issues of Genetic Engineering with...
