Rite & Reason: The central issue for the Catholic Church remains what it always was - the deliberate killing of an innocent human being is never justifiable, writes Fr Kevin Doran
In reading St Thomas, or indeed any philosopher prior to the 19th century, we have to take into account the fact that cellular biology is a relatively recent discovery. While St Thomas was a keen observer of the natural world, the church would not claim any expertise for him in the field of embryology.
In his recent article, Patsy McGarry finds it odd that the Catholic Church's teaching on the origins of life should take account of developments in the natural sciences. I would argue that this is simply a sign of the church's maturity. The church is not threatened by truth whatever its source. The central issue for the Catholic Church remains what it always was, namely that the deliberate killing of an innocent human being is never justifiable.
If the natural sciences help us to understand when individual human life begins, so much the better.
The Christian theology of body and soul was developed against the background of Aristotelian and Thomistic metaphysics. St Thomas Aquinas, like Aristotle before him, argued that everything in the material world is composed of matter and form. Matter determines the quantity or extent of a thing, and divides it from other things of the same kind, while form gives the thing its "quiddity", ie determines the kind of thing it is.
For St Thomas, all living things in the material world have a form which acts as the first principle of life, and which accounts for the characteristic activity of that species of things. The forms of living things are known as "souls". Just as there is no material substance without a substantial form, so there is no living material substance which does not have a soul as its first principle of life. Plants, according to St Thomas, would have a vegetative soul which accounts for their growth and reproduction. Similarly, animals would have a "sensitive" soul which, in addition, would account for all the activity associated with sense psychology, such as movement, pain and pleasure.
The characteristic activity of the human species is rational or intellectual activity and this, according to Thomas, is explained and made possible by a rational soul which is the first principle of life in a human being.
As the first principle of life, the soul does not come in as it were from outside. The rational soul is an integral part of a human being from the first moment of its existence. Otherwise it couldn't live and grow and eventually do the things which, of their nature, humans do.
It will be argued, of course, that rational functioning does not begin until children are two or three years old. There is a principle in scholastic philosophy which addresses this issue. It is the principle "opera sequiter esse (action follows from being)". To put it simply: we don't become human by acting rationally; rather we act rationally - some of the time, let it be said - because we are human beings.
Within the Catholic tradition, parents are described as pro-creators. This is because their act of love, which gives rise to the fusion of sperm and ovum, is seen as corresponding with another act of love on the part of God, who creates the life principle or soul of the new organism, allowing it to live, to grow and to function coherently.
The fact that some embryos are generated in laboratories and others come into being through an act which is less than loving, certainly has the potential to obscure the meaning of the pro-creative act, but it does not fundamentally alter God's loving design for this new human being which would never begin life without His creative act.
So when does individual human life begin? Modern genetics has helped us to clarify this issue by demonstrating that the new organism which comes into existence at fertilisation is genetically unique and distinct from either of the parent organisms. We also know that fertilisation is a process rather than an instantaneous event.
The fusion of the genetic information from the sperm and the ovum takes some hours. Long before this process has been completed, however, the cytoplasmic contents of the sperm and the ovum have come into direct continuity and formed one single cell, which has an organic unity and is oriented towards ongoing development. This pro-nuclear embryo contains all the genetic information of the new human being, albeit in a process of dynamic reorganisation.
Some may prefer to think of humans as nothing more than complex organisms. Biological scientists are wise to acknowledge that they cannot make factual statements about what is metaphysical, ie beyond the physical world.
The fundamental logic of Aquinas's theory certainly goes beyond the boundaries of the natural sciences, but it does not conflict with the truths of modern science. I believe, however, that our human capacity for rationality is evidence enough of a metaphysical life principle, ie one which the physical sciences cannot explain, which informs the human body from fertilisation to natural death.
If we follow the logic of St Thomas, the new human being which already exists at the pro-nuclear stage must have such a first principle of life - a soul - which is capable of accounting for its development.
Fr Kevin Doran is secretary of the Catholic bishops' committee for bioethics