What is a human being?

The long awaited report of the select committee on In Vitro Fertilisation has been published. The evidence you had given before the parliamentary committee had aroused much controversy at the time. For instance, you thought freezing embryos more extensively tolerable than most moral theologians do, while you did not think that for a couple to be “in a stable relationship” provided sufficient protection for a future child’s rights. However, I do not intend to raise the dust of those discussions again now. I am only asking you to clarify your position on a very pertinent basic philosophical question, namely at what point is it that a distinct individual human being actually comes into existence?

Itake it to be when the body is sufficiently organised for it to support such typically human operations as thinking. This formulation still allows a range of opinions when it comes to determine the moment more precisely. Even among Thomists, the views range from those of such philosophers as John Haldane, who hold that a rational soul is “present at conception, i.e. at fertilisation”, to those of other philosophers such as Robert Pasnau, who hold that it is only when the brain is fully developed and can support conceptual operations.

Thomas Aquinas cannot have intended his position to be interpreted as Pasnau does, if for no other reason because Aquinas explicitly held that the rational soul was infused at 40 days for males and at 90 days for females, and he certainly knew that there was not a fully developed human brain until well after birth.

The most plausible interpretation of Aquinas is surely that there is a distinguishable human being in existence when there is a body in which it is possible to discern that some structures had actually begun to exist with inbuilt tendencies for self-development into organs for such specifically human activities as thinking.

However, Haldane’s identification of this moment with that of “conception, i.e. fertilisation” still leaves room for differences. Fertilisation is a process that may be considered to start with the penetration of sperm into ovum and to last at least until syngametisation, or the coming into existence of a distinct DNA. This process is set to last some 24 hours.

Even if the moment of “ensoulment” or hominisation is fixed at the end of the period of “conception” or “fertilisation”, the life in the cellular body in question is definitely human, although not an individual distinct from its parental source. It has therefore to be treated with due respect and with additional prudence because of the doubt that its destruction might be murder rather than mutilation. But clearly there are contexts in which such destruction may not be morally wrong.

Does Pasnau support his position with any argument other than that of taking words at their most obvious face value?

He argues that as long as there is the possibility of (monozygotic) twinning, i.e. up to about day 13 from fertilisation, there cannot be said to be a human individual. There is only a group of cells from which one or more human beings will develop.

Indeed, a fertilised egg, at its very early four-cell stage, could still have each of the four cells separating from the others and developing independently into an embryo.

Haldane, arguing against Pasnau, puts forward an analogy. One flat worm can by division result in two whole flat worms. Parts of a flat worm have the potential to become a whole flat worm when isolated from the present whole of which they are part.

Likewise, at the early stages of human embryonic development, the degree of cell specialisation will not have progressed very far. Therefore, each cell or group of cells can become a whole organism if divided from the rest and provided with an appropriate environment after the division.

However, that does not imply that prior to the division the embryo was a mere mass of cells rather than a single, complex, actively developing human organism.

To me, the comparison seems to limp badly. The flat worm divided into two is clearly an autonomous organism. The group of cells which develops into one of a pair of twins is not manifestly that. Whether it is or not is precisely what is in dispute. What the flat worm analogy shows is that the possibility of twinning on its own does not exclude the possibility that the twins may have emerged from what was a unitary organism.

Haldane seemingly recognises that other grounds have to be given for holding that there is a distinct individuality from the very beginning. He puts forward two such grounds.

The first is interactivity between the cells, but that does not prove that there is substantial unity between them to the exclusion of their belonging to different organisms.

The second ground is that in the cells in question (even before implantation), there are inbuilt forces “restraining them (the cells) from individually developing as whole organisms and directing each of them to function as a relevant part of a single whole organism continuous with the zygote”.

But once again this observation does not seem to me to provide a clear criterion for the appearance of a new individual with substantial unity.

What then establishes the existence of a distinguishable human being?

The existence of a distinct DNA. The DNA can be said to provide a complete blueprint for the body’s development. For this reason the DNA can be considered to provide the primordia of the organs, the full development of which will allow specific human operations to occur.

Fr Peter Serracino Inglott was talking to Miriam Vincenti.