PATERNITÀ, RICERCA della. – While from the ethical point of view the r. of p. may be considered lawful in itself, various civil codes, for reasons of expediency, admit investigations into paternity only in cases expressly provided for. This prohibition originated in the French revolutionary laws, from which it passed into the Napoleonic Code.
Art. 269 of the Italian Civil Code admits a judicial declaration of paternity: 1) when the mother and the presumed father notoriously cohabited as husband and wife during the period to which conception can be attributed; 2) when paternity is indirectly established by a civil or criminal judgment, or by an unequivocal written declaration of the person to whom it is attributed; 3) when abduction or carnal violence occurred during the period corresponding to that of conception; 4) when there is possession of the status of a natural child (v. PROLE).
In certain civilized countries the problem of investigating paternity is acquiring new aspects (in the United States of America there are legally recognized societies authorized to bring the presumed father before the courts), and the biological sciences are pursuing their studies in order to establish the principles on which proof of paternity can be based; particular mention should be made of the biological test based on blood groups.
Human blood contains two agglutinogens, called agglutinogen A and agglutinogen B, attached to the red blood cells. Blood serum, in turn, contains two agglutinins, α and β. Four blood groups have been distinguished: Group I: possesses no agglutinogens but possesses both agglutinins; it is group O, or that of universal donors; Group II: group A, provided with agglutinogen A and agglutinin β, or anti-B; Group III: possesses agglutinogen B and agglutinin α, or anti-A; Group IV: (AB), which contains both agglutinogens and lacks agglutinins; it is the group of universal recipients. When blood containing a given agglutinogen is brought into contact with other blood containing the corresponding agglutinin, the phenomenon of isoagglutination occurs: the red blood cells become agglutinated, and under the microscope irregular accumulations of them can be observed. In practice, blood-group testing is carried out by means of test sera. An individual’s blood group is a constant, congenital character, inherited from the parents according to Mendelian laws. It undergoes no qualitative alteration during life; at birth there is an incomplete quantitative development of the agglutinogens, which possess approximately one-fourth or one-eighth of the receptive strength they have in adults; this strength increases until it reaches its maximum at about 15–20 years of age and remains at that level into advanced age. For this reason, errors in group determination may occur in newborns and infants.
Knowledge of the following laws is important: 1) properties A and B are dominant characters with respect to O, and are therefore found in children only when they are also present in the parents; however, even when present in the parents, they may fail to appear in the children; property O, on the other hand, being recessive, may be found in children even if it is not manifested in the parents; 2) parents belonging to group O cannot have children of group AB; parents belonging to group AB cannot have children belonging to group O. In 1927 Landsteiner and Levine demonstrated new agglutinogens, in addition to agglutinogens A and B, to which no preformed agglutinins correspond in the blood of other individuals; these are the blood groups designated respectively M, N, and MN. Subsequently agglutinogen P was also discovered, and in 1940 Landsteiner and Wieser identified agglutinogen Rh, present in approximately 85% of men, who are consequently assigned to the Rh-positive group, while 15% belong to the Rh-negative group. From these findings two further laws emerged: 1) properties M and N are dominant properties and cannot appear in children if the parents lack them; 2) properties M and N are allelomorphic properties: for this reason property M (without N) or property N (without M) must appear in the children if they are present singly in the parents, provided that they occur in the pure state. By determining the blood groups present in the blood of the mother, the child, and the presumed father, and comparing them with the data in appropriate tables, it is possible to arrive at the exclusion of paternity. In practice, group compatibility is not regarded as evidence of an actual filiation relationship, whereas, conversely, in cases of incompatibility the exclusion of the presumed father can be asserted with certainty.
In recent times, further research has been conducted on group-specific systems, especially by foreign authors. The various subgroups of A, namely A₁, A₂, A₃, etc., have been studied, and importance has been attached to them not only qualitatively but also quantitatively; importance has likewise been attached to the considerable rarity of the subtypes A₃, A₁, A₂, A₃, N₂, and N₃. For example, the establishment of A₄ in the presumed father and the child, which is observed with a probability of one in a million, led Hirsfeld and Amsel to regard paternity as established. The same may be said of the importance attached to the rarity of certain genotypes of the Rh system and to the rarity of the Leway, Celano, etc. factors.
Research has also been conducted, and is still under way, in Italy, although it is limited by the difficulty of obtaining the necessary sera. According to recent research, the current probabilities of excluding paternity in the various mother–child combinations reach, for Italians, as much as 90.8% for the principal properties A B O, MN, and Rh alone. Higher probabilities are obtained if the investigation is extended to the P system, to N, and to the principal Rh subtypes.
The importance of this group-specific research for resolving, from the biological point of view, the much-debated problem of investigating paternity cannot therefore be denied.
Maria De Arcangelis