The Independent in in letters column on Sunday January 20th has published an excellent letter from Professor William Reville of University College Cork, under the heading "Embryo starts the continuum of life". The letter is reprinted in full below and is also viewable on the above link.
Madam – I refer to the article by Senator John Crown on the subject of abortion (Sunday Independent, January 13, 2013). I agree with much of what he said, but I entirely disagree with the point he made at the end of his article where he claimed that the early human embryo "is a form of life in the same sense that a sperm or a cancer cell growing in a dish is a form of life". This opinion is simply wrong – it contradicts elementary biological facts.An individual human life begins at conception when a sperm cell from the father fuses with an egg cell from the mother, to form a new cell, the zygote, the first embryonic stage. The zygote grows and divides into two daughter cells, each of which grows and divides into two grand-daughter cells, and this cell growth/division process continues on, over and over again.The zygote is the start of a biological continuum that automatically grows and develops, passing gradually and sequentially through the stages we call foetus, baby, child, adult, old person and ending eventually in death. The full genetic instructions to guide the development of the continuum, in interaction with its environment, are present in the zygote. Every stage along the continuum is biologically human and each point along the continuum has the full human properties appropriate to that point.On the other hand, neither the sperm cell nor the cancer cell mentioned by Senator Crown has the capacity to develop along a continuum into an adult human being, or indeed the capacity to develop into anything useful beyond themselves. These cells have specific roles and limited capacities and are completely different from the early embryo.Many pro-choice people see the early embryo as a potential human being. However, it is clear to me, and to many others, that the biological data tells us the early embryo is a human being with potential.