Under the Microscope: Debate on the status of the human embryo is before us again in Ireland. If the embryo is fully human, we are obliged to protect it from harm. Opinions differ among experts on the status of the embryo, but I believe that a strong case, consistent with science, can be made for the full humanity of the embryo.
The story of human life begins at conception when a sperm cell from the father fuses with an egg cell from the mother to produce a unique new entity called a zygote. The zygote is a single cell. It divides to produce two cells, which again divide to form four cells, and so the process continues. After a few cycles of cell division, the entity is called an embryo. The cells continue to divide and differentiate to form the foetus which develops in the womb into a baby, who is born and develops through childhood into an adult who grows old and dies. The whole process from zygote to death is a continuous unfolding between two boundary conditions - conception and death.
Each of us was once a zygote. The full genetic plan that directed our development into mature adults was present in the zygote. No new genetic information was added along the way. Human life is obviously present at all stages - zygote, embryo, fetus, child, adult, old person - because the cells are alive and of the species Homo sapiens. But when does full human life begin?
I believe that full human life begins at conception. Each stage of subsequent development occurs on a continuum and each is the full expression of humanity appropriate to its stage. For example, I am a very different entity now to what I was as a newborn baby, but nobody would dispute that both conditions are fully human.
Within a week of conception, the embryo implants in the mother's womb where it develops very rapidly. A primitive heart muscle beats after about three weeks. Other organs begin to develop during the first month - liver, kidneys, digestive tract, and so on. Towards the end of the first month, arms and legs are discernable as tiny buds.
Over half of the embryos that are produced either fail to implant in the womb or are otherwise lost. An embryo that fails to implant dies.
It is logical to choose conception as the instant at which full human life begins because this event marks a clear and momentous qualitative change. To pick a point on the subsequent continuum as marking the beginning of full human life must always be an arbitrary decision.
The tiny zygote can only be seen through a microscope at high magnification. It has no nervous system and can feel no pain or anxiety. It is so different in size, appearance and capacity from its size, form and capacity at later stages of development that it is easy to think of it as a qualitatively different thing and to judge it by special criteria.
But, the zygote is not qualitatively different from the human adult, just quantitatively different. It has the full potential to develop under normal conditions from its quantitative tininess into a human adult.
Many people argue that we need not regard the embryo as being fully human before it implants in the womb. After all, they argue, if it fails to implant, it will die. This argument unfairly penalises the embryo on the basis of size, capacity and geography. Most people who make this argument would be appalled to see those criteria applied at a later stage of development.
For example, imagine assigning human rights to a very small person in proportion to his size relative to average size. Imagine condoning infanticide in parts of the world where infant mortality rates are high. Imagine denying basic social services to people who live in remote areas.
Many people shy away from according legal protection to the human embryo because of the practical consequences - abortions would not be allowed except in the most circumscribed circumstances, spare embryos destined for eventual destruction could not be made for in vitro fertilisation (IVF), and human embryonic stem-cell research could not go ahead because harvesting these stem cells destroys the embryo.
It is feared that denying abortion on demand would lead to an upsurge of illegal "back street" abortions. I can see this would be a problem. But what about the problem we have now? UK figures show that one in four pregnancies are aborted. Clearly abortion is being used as contraception, even though artificial contraception is universally available. Responsible use of contraception would reduce unwanted pregnancies to a rarity. Which is the bigger problem - the current avalanche of unnecessary abortions or a trickle of demand for abortion that cannot be satisfied if we legally protect the embryo?
I have no ethical objections to IVF in principle. In IVF, egg cells are fertilised by sperm cells in a petri dish. The resulting embryos are examined and the best looking are implanted in the woman. The remaining "surplus" embryo are frozen and stored. Inevitably, most of these frozen embryos are destined to eventually die. The technique of IVF should be improved so that, somehow, surplus embryos are not generated.
Finally, stem cells are also available, without any ethical problems, from adult tissues and umbilical cord blood. Research on these cells promises to yield, albeit with greater difficulty, the same results in producing cures for human diseases as does research on embryonic stem cells.
William Reville is associate professor of biochemistry and public awareness of science officer at UCC - http://understandingscience.ucc.ie