This process of disaggregating the blastocyst’s cells eliminates its potential for further development.
Opponents of HESC research argue that the research is morally impermissible because it involves the unjust killing of innocent human beings.
The issue of when a human being begins to exist is, however, a contested one.
The standard view of those who oppose HESC research is that a human being begins to exist with the emergence of the one-cell zygote at fertilization.
The prospect of our going out of existence through fission does not pose a threat to our current status as distinct human persons.
Likewise, one might argue, the fact that a zygote may divide does not create problems for the view that the zygote is a distinct human being.This view is sometimes challenged on the grounds that monozygotic twinning is possible until around days 14–15 of an embryo’s development (Smith & Brogaard 2003).An individual who is an identical twin cannot be numerically identical to the one-cell zygote, since both twins bear the same relationship to the zygote, and numerical identity must satisfy transitivity.At this stage, human embryos are said to be “whole living member[s] of the species homo sapiens …[which] possess the epigenetic primordia for self-directed growth into adulthood, with their determinateness and identity fully intact” (George & Gomez-Lobo 2002, 258).That is, if the zygote, A, divides into two genetically identical cell groups that give rise to identical twins B and C, B and C cannot be the same individual as A because they are not numerically identical with each other.This shows that not all persons can correctly assert that they began their life as a zygote.However, most of those who oppose the research argue that the constraints against killing innocent persons to promote social utility apply to human embryos.Thus, as long as we accept non-consequentialist constraints on killing persons, those supporting HESC research must respond to the claim that those constraints apply to human embryos.Thus, the controversies around HESC research will continue, at least in the near-term.While the principal source of the controversy surrounding HESC research lies in competing views about the value of human embryonic life, the scope of ethical issues in HESC research is broader than the question of the ethics of destroying human embryos.