Select Committee on Stem Cell Research Report


The development of the embryo

4.1 In such a sensitive area as research on human embryos, terminology is very important. Debate is often clouded by misconceptions of the stages of human development. The following paragraph outlines the various stages of embryonic development. A glossary of biological terms used in this report is at Appendix 5.

4.2 The development of the embryo is a continual process of change. For convenience it can be described in terms of the following seven stages:

    (a)  The female egg ("oocyte") is fertilised by the male sperm. The process of fertilisation consists of a number of steps which ultimately result in a single cell, the"zygote". The egg and sperm each carry half the genes of a normal cell. The zygote contains all the genes necessary for the development of an individual, half derived from the mother and half from the father. (As described in paragraph 5.15, a very small proportion of genes are contained in the mitochondria and are inherited exclusively from the mother.)

    (b)  The zygote undergoes a series of cell divisions starting some 36 hours after the beginning of fertilisation. Initially (up to the eight cell stage) all the cells are essentially identical and all have the potential, if placed in the right environment, to develop into an individual. Indeed, identical twins result from the splitting of the cells at this early stage: they are genetically identical as a result of developing from the same fertilised egg. One or more cells can be removed from the zygote at this stage without impairing development. This is illustrated in preimplantation diagnosis during IVF (which in the United Kingdom is permitted only to prevent serious genetic disease) in which a single cell is removed at the eight cell stage for genetic analysis. The remaining seven cell zygote can be implanted and develop normally.

    (c)  When the developing embryo reaches about 100 cells (still smaller than a pinhead) it is known as a blastocyst. The blastocyst is a small hollow ball of relatively undifferentiated cells. Many of the cells in the blastocyst go on to develop into non-embryonic tissues such as the placenta or umbilical cord. However, within the blastocyst is a population of cells, the inner cell mass, from which ES cells can be derived and from which the embryo itself develops. The properties of ES cells were described in Chapter 2. As the source of ES cells, the blastocyst is the primary focus of much of the debate on the use of embryos in stem cell research and therapy. It is sometimes referred to as the preimplantation embryo. In this report we use the term "early embryo" to cover stages of development up to the appearance of the primitive streak (see (e) below).

    (d)  About a week after fertilisation implantation of the blastocyst in the womb takes place. If implantation does not take place, the blastocyst does not develop further: it does not go through the stages of embryonic development, and cannot become a foetus; specific biochemical signals from the mother are required for further development. A substantial proportion of early embryos—many estimates put it as high as 75 per cent—are naturally lost before implantation. At this stage the cells are still relatively undifferentiated and there is no trace of human structure such as a nervous system, and hence there can be no sentience.

    (e)  At about 14 days after fertilisation, following implantation, the early embryo consists of about 2000 cells. It is only at this stage that the cells begin to become differentiated into more specialised cell types, and the "primitive streak", from which the central nervous system eventually develops, begins to appear.

    (f)  After about seven weeks' development, individual organs become recognisable and the embryo can properly be described as a foetus.

    (g)  At around nine months, given normal gestation, the baby is born.

The status of the early embryo

4.3 The starting point for consideration of the ethics of research on human embryos is the status of the early embryo. This was one of the most fundamental questions facing the Committee since it is intimately bound up with the questions of when human life begins and of the definition of a person.


4.4 Although there have been many scientific developments since the Warnock Committee reported, the basic ethical arguments have not changed substantially since then. Positions range from those taken by pro-life groups and some of the churches that the early embryo is a human being in the fullest sense from the moment of fertilisation and should be accorded the same respect as a human foetus or baby, to the position that, because at the earliest stage of its development the embryo is no more than a collection of undifferentiated cells, albeit with the potential to develop into a human being, it deserves little more attention than any other isolated human cell or tissue.

4.5 The Warnock Committee adopted a position between these opposing views, concluding that the early embryo has a special status but not one that justifies its being accorded absolute protection. That view was enshrined in the 1990 Act.


4.6 The debate centres on the concept of respect for persons. Most people accept the idea that persons should be respected, although they may mean various things by this claim; and it is commonly agreed that babies, children and adults are persons. Many believe that the foetus is a person. The main area of disagreement is whether the early embryo is, or should be treated as if it is, a person.

4.7 One common claim about respect for persons is that it demands that we do not treat others merely as means, and in particular that we do not undercut or bypass their capacities to act. Where capacities to act are lacking—for example in infants—similar forms of respect are extended. However, the basic arguments for respect are focused on persons thought of in the ordinary way as beings able to think, act and communicate.

4.8 For those who take the view that the early human embryo has all the rights of a person, it follows logically that it is owed full respect and that no research which has the effect of destroying the embryo is permissible.

4.9 Many of the arguments advanced by those who hold this position are theological (see paragraphs 4.18-4.19). However, two arguments are more widely put forward. The first advances the view that, as the early embryo has the potential to become a person, it enjoys the full rights of a human being and should be accorded the respect owed to a human being. The second argument contends that since the embryo is alive it has a right to life.

4.10 Those who deny the force of the potentiality argument argue that the fact that a person has the potential to qualify as a member of some class in the future, if certain conditions are met, does not confer the rights that belong to members of that class of being until those conditions are met. A medical student is a potential physician, and if he or she qualifies may practise as such; but the potentiality alone does not confer a right to practise. A child is a potential voter but has no claim to be treated as a voter until reaching the age of 18.

4.11 Claims that the embryo is a person from the moment of fertilisation are hard to reconcile with standard views of human and personal identity. Although a baby's mental capacity is undeveloped, there is a continuity of identity between the baby and the adult it will become. So we say, looking at a photograph, "That was me as a baby". When it comes to the undifferentiated cells of the blastocyst, however, such a continuity of identity is less plausible. Those cells also form the placenta and umbilical cord. Furthermore, they can divide to form identical twins. Because there is not the same continuity of identity it is more natural to refer to these undifferentiated cells as a potential person rather than as a person.

4.12 Some would see this view as underpinned by embryological evidence. Although the fertilised egg and blastocyst contain all the genetic signals required for human life, this is true of nearly all cells in the body. However, genetic elements are not sufficient and there is no automatic programme of development from blastocyst to birth. Although the early embryo contains within it the full genetic potential of any person(s) who may develop from it, it requires many other factors, particularly those provided by the maternal environment in the womb, to enable it to realise that potential.

4.13 A gradualist view of the development of the embryo is also seen as consistent with the way cultures react to early embryo loss. Although would-be parents may feel sad at the natural loss of early embryos before implantation, there is no public mourning ritual associated with it, nor is there for the loss of surplus embryos left over from IVF treatment.

4.14 The argument that because the embryo is alive it has a right to life has little weight unless linked to the potentiality argument. The fact that a cell or piece of human tissue is alive is not in itself a reason for according it a full right to life. The claim that an embryo has a full right to life assumes not merely that it is alive, but that it has a status that most living tissue does not have—the very point that has to be established if the embryo is to have a right to life.

4.15 Some of those who ascribe full rights to the early embryo argue that, even if it has not been demonstrated that the early embryo is a person, equally it has not been demonstrated that it is not a person. They suggest that early embryos should therefore be given the "benefit of the doubt": even if they are not persons they should be treated as if they were persons, and accorded the full rights that we accord to persons.

4.16 Burden of proof arguments are notoriously hard to resolve. If there were no morally serious reasons for undertaking research on human embryos, then the mere possibility that the early embryo is a person would be sufficient reason not to do such research. However, if there are morally weighty reasons for doing such research a decision must be reached on the basis of arguments that fall short of proof.

4.17 There are morally weighty reasons for doing research that may lead to therapies for many serious and common diseases, and the concept of respect for persons can also be invoked on this side of the argument. A commitment to respect for persons is fundamental to many areas of life, not least the practice of medicine, in which help and assistance to those in need is a guiding principle. Here respect for persons may take the form of developing treatments for serious degenerative diseases, and there can be few causes more worthwhile than to relieve the suffering caused by these diseases. We received a good deal of evidence from people suffering from such diseases, particularly Parkinson's disease, which illustrated this. It would be wrong not to seek therapies for such diseases, which necessarily involves undertaking the fundamental research that may make those therapies possible. Unless early embryos have an unconditional claim to protection, therefore, it would be wrong to rule out research involving them for such a purpose.


4.18 The various positions set out in the previous section are also found in the teaching of religious bodies. On the one hand, there are those that teach that the early embryo must be fully protected from the moment of conception. On the other hand, there are those that take a gradualist position. And there are differences of view and emphasis within many of these religious traditions. Amongst those that take an absolutist view of the status of the early embryo and the protection to be accorded to it, the Roman Catholic Church is opposed in principle to any destructive interference with the early embryo. The Catholic Catechism states that, "Human life must be respected and protected absolutely from the moment of conception".[29] The basis of this view is that either the early embryo is a person or, even if it may not be, as long as there is not total certainty that it is not a person, it must be given the benefit of the doubt and treated as if it were. This view is shared by some other Christians. It was also put to us as the Muslim view by the Islamic Medical Association, "He/she should be fully respected from the moment of conception and the fertilised egg is a sacred being" (p ). We understand that the Hindu view is similar, reflecting the fact that traditional Hindu thought regards abortion as a major transgression.[30]

4.19 Some other Christian Churches interpret the Christian tradition differently from the Roman Catholic Church.[31] They take the view that the early embryo is not yet a person and that its potential to become one does not give it a claim to be treated as a person. On this reading of the Christian tradition the respect to be accorded to an early embryo is not absolute from the moment of fertilisation but develops as the embryo develops. Thus in giving evidence with the Board for Social Responsibility of the Church of England the Bishop of Rochester referred to "taking a developmental view of the emergence of personhood" (Q160). The evidence we received from the Court of the Chief Rabbi stating the Jewish position also put forward a gradualist position:

    In Jewish law neither the foetus nor the pre-implanted embryo is a person; it is, however, human life and must be accorded the respect due to human life. Personhood, with its attendant rights and responsibilities begins at birth. Prior to birth, we have duties to both the embryo and the foetus, but these may, in certain circumstances, be overridden by other duties, namely those we owe to persons (p 60).


4.20 The debate on the moral status of the early embryo will no doubt continue. Members of the Committee have different views of the strength of the arguments set out above. But, whatever those individual views, the Committee believes that the question of research on human embryos has to be considered within the context of the law in the United Kingdom and the social attitudes it reflects. There are three main elements to this:


4.21 Whilst respecting the deeply held views of those who regard any research involving the destruction of a human embryo as wrong and having weighed the ethical arguments carefully, the Committee is not persuaded, especially in the context of the current law and social attitudes, that all research on early human embryos should be prohibited.

The fourteen days limit

4.22 If the respect to be accorded to an embryo increases as it develops, this is a gradual process and it may be difficult to establish precisely the point of transition from one stage to the next. The 1990 Act established 14 days as the limit for research on early embryos. Fourteen days has an objective justification insofar as it represents the stage at which the primitive streak, the precursor of the development of a nervous system, begins to appear. This limit seems to have been widely accepted, and the research done under the Act under licence from the HFEA has attracted very little criticism from those who accept the case for research on early embryos. We have received no evidence to suggest that, if research on human embryos is to continue, there should be a different limit. In point of fact the stage at which stem cells need to be extracted for research is very much earlier than that—at the blastocyst stage—when the early embryo is still smaller than a pinhead. The Committee considers that 14 days should remain the limit for research on early embryos.

What does respect for the early embryo mean in practice?

4.23 The Warnock Committee recommended that "the embryo of the human species should be afforded some protection in law" but that protection could be waived in certain specific circumstances.[33] Some of our witnesses took issue with the idea of a status that attracted only limited protection, arguing that it was hypocritical to profess respect for something you were going to destroy. It is true that if an embryo had full human rights it would be inconsistent to do anything that had the effect of destroying it. But to maintain a position that falls short of total protection for the embryo does not in our view equate to a total absence of respect.

4.24 Nevertheless there can be confusion about how respect for an embryo should be demonstrated. It may be helpful to try to clarify it. It is sometimes assumed that respect simply means the respectful treatment and disposal of embryonic tissue in the laboratory. This is certainly important, as with any human tissue. The reaction to the removal of organs from children at Alder Hey Hospital shows the importance attached to the physical treatment of human tissue, in that case body parts, even when it is no longer alive.

4.25 When living tissue is involved, a further degree of sensitivity is necessary. The 1990 Act requires this to be demonstrated in the following ways:

    (a)  through the extensive restrictions that are rightly placed on the use of embryos—the 1990 Act permits research on embryos to be carried out only if there is no alternative available and it is necessary or desirable to achieve one of the permitted purposes;

    (b)  through strict adherence to the rules governing the informed consent of the donors (we return to this issue in Chapter 8);

    (c)  through restrictions on export where restrictions on use after export could not be overseen or enforced;

    (d)  through restrictions on mixing with non-human material; and

    (e)  through meticulous record-keeping of the creation and disposal of early embryos for research so that every embryo is accounted for.

The creation of embryos for research

4.26 At present research on embryos is conducted almost exclusively on embryos created for the purpose of IVF treatment which are surplus to requirements and are donated specifically for research purposes. Between 1 August 1991 and 31 March 1999 53,497 surplus embryos were donated for research.[34] The 1990 Act also permits the creation of embryos for research. This was an issue on which the Warnock Committee was divided. It recommended by only a narrow majority in favour of allowing the creation of embryos for this purpose. Since the Act came into force 118 embryos have been created for research.

4.27 The creation of embryos (whether by IVF or CNR) for research purposes raises difficult issues. Some argue that, if an embryo is destined for destruction, it is more honest to create it specifically for the purpose of research than to use one created for reproductive purposes. But most of those who commented on this issue regarded it as preferable to use surplus embryos than to create them specifically for research. They took the view that an embryo created for research was quite clearly being used as a means to an end, with no prospect of implantation, whereas at the time of creation the surplus embryo had a prospect of implantation, even if, once not selected for implantation (or freezing), it would have to be destroyed. We agree that for this reason it is preferable to use surplus embryos for research purposes if the same results can be achieved with them. It is currently unavoidable that there should be some surplus embryos from IVF treatment, although desirable that the numbers should be reduced as more effective techniques are developed.

4.28 There may, however, be some research needs for embryos that cannot be met by the use of surplus embryos, for example when the research is concerned with the act of fertilisation itself. Two examples of such research that were licensed by the HFEA are: to test techniques of freezing eggs, which are very fragile, in order to assess the normality of an embryo created from an egg that has been thawed and fertilised; and the development of Intra-Cytoplasmic Sperm Injection. This procedure involves the direct injection of a sperm into an egg as a means of securing fertilisation by immature sperm. It was necessary to create an embryo to test the effectiveness of the technique and demonstrate its safety.[35] The very small number of embryos created over the last ten years suggests that in practice there is little demand to create embryos by IVF for research. The Committee believes that embryos should not be created specifically for research purposes unless there is a demonstrable and exceptional need which cannot be met by the use of surplus embryos.

29   Paragraph 2270. Back

30   The Bahá'? view is, similarly, "that any cell, group of cells or embryo having the potential to develop into a separate individual is sacred and has a soul." (Memorandum by Bahá'? Community of the United Kingdom (p 227)). Back

31   The different interpretations of the Christian tradition are described in Appendix 4. Back

32   The original limit of 28 weeks in the Abortion Act 1967 was reduced to 24 weeks by the 1990 Act (section 37 (1)(a)). Back

33   Paragraph 11.17. Back

34   HFEA, Ninth Annual Report and Accounts, 2000. More up to date figures are not yet available. Back

35   Q 7. Back

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