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'Human Embryo in the Pre-Implantation Phase'

Communiqué From Pontifical Academy for Life

VATICAN CITY, MAY 2, 2006 (Zenit) - The 12th General Assembly of the Pontifical Academy for Life issued this final communiqué March 23 after the international congress on "The Human Embryo in the Pre-Implantation Phase."

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On the occasion of its 12th General Assembly, the Pontifical Academy for Life celebrated an international Congress on the theme: "The human embryo in the pre-implantation phase: Scientific aspects and bioethical considerations." At the conclusion of the congress, the academy offered to the ecclesial community and to the general public, certain considerations on the theme of its reflection.

1. It can escape no one that the contemporary bioethical debate, especially in recent years, has focused mainly on the reality of the human embryo, considered in itself or in relation to how other human beings behave toward it. This is only natural since the multiple implications (scientific, philosophical, ethical, religious, legislative, financial, ideological, etc.) connected to these areas inevitably catalyze different interests, as well as attract the attention of those in search of authentic ethical action.

The need to ask the basic question: "Who or what is the human embryo," has therefore become unavoidable, in order to draw from a relevant, consistent answer to this question criteria for actions that fully respect the integral truth of the embryo itself.

To this end, in accordance with a correct bioethical methodology, it is necessary first of all to look at the data that the most up-to-date knowledge puts at our disposal today, enabling us to know in great detail about the different processes through which a new human being begins its existence. These data must then be subjected to an anthropological interpretation in order to highlight their significance and the emerging values to which to refer in the last place, to derive the moral norms for practical action and standard procedures.

Human life begins at conception

2. Consequently, in light of the most recent discoveries of embryology, it is possible to establish certain universally recognized points:

a) The moment the sperm penetrates the oocyte is when the existence of a new "human being" begins. Fertilization induces a whole series of consecutive events and transforms the egg cell into a "zygote." In the human species, the nucleus of the spermatozoid (contained in the head) and a centriole (which will play a determining role in the formation of the mitotic fusus in the act of the first cellular division) enter the oocyte; the plasmatic membrane remains on the outside. The male nucleus undergoes profound biochemical and structural changes that depend on the ovular cytoplasm in preparation for the role that the male genome will immediately begin to play. Here we are witnessing the decondensation of the chromatin (induced by factors synthesized in the final phases of ovogenesis) that makes transcription of the paternal genes possible.

After the sperm penetrates the oocyte, it completes its second meiotic division and expels the second polar body, reducing its genome to a haploid number of chromosomes in order to associate with the chromosomes brought by the male nucleus the karyotype characteristic of the species. At the same time, it encounters an "activation" from the metabolic viewpoint, with a view to the first mitosis.

It is always the cytoplasmatic environment of the oocyte that induces the centriole of the spermatozoon to duplicate itself, thereby constituting the centrosome of the zygote. This centrosome duplicates itself with a view to constituting the microtubule that will make up the mitotic fusus.

The two sets of chromosomes find the mitotic fusus already formed and arrange themselves at the equator in a position of metaphase. The other phases of mitosis follow, and finally the cytoplasm divides and the zygote gives life to the first two blastomeres.

The activation of the embryonic genome is probably a gradual process. In the single-cell human embryo seven genes are already active; others are expressed during the passage from the zygote stage to that of two cells.

b) Biology, and more particularly embryology, provides the documentation of a definite direction of development: This means that the process is "oriented" -- in time -- to the direction of a progressive differentiation and acquisition of complexity and cannot regress from the stages it has already completed.

c) A further point acquired with the earliest phases of development is the "autonomy" of the new being in the process of the auto-duplication of genetic material.

d) The characteristics of "gradualness" (the time needed for the passage from a less differentiated stage to a more differentiated stage) and of the "coordination" of ...

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