Paternity, Research into. — While from an ethical standpoint the research into paternity may be considered licit in itself and for its own sake, various civil codes, for reasons of expediency, do not admit investigations into paternity except in cases expressly provided for. This prohibition has its origin in the French revolutionary laws from which it passed into the Napoleonic Code.
Art. 269 of the Italian Civil Code admits judicial declaration of paternity: 1) when the mother and the presumed father notoriously cohabited as spouses at the time to which the conception is traced; 2) when paternity is indirectly evidenced by a civil or criminal judgment or by an unequivocal written declaration of the person to whom it is attributed; 3) when there has been abduction or rape at the time corresponding to that of the conception; 4) when there is possession of status as a natural child (v. PROLE).
In some civilized countries the problem of researching paternity is taking on new aspects (in the United States of America there exist legally recognized societies authorized to bring the presumed father to trial), and the biological sciences are advancing their studies in order to establish principles upon which to base proof of paternity; special mention should be made of the biological proof of blood groups.
In human blood there exist two agglutinogens called agglutinogen A and agglutinogen B, linked to the red blood cells. The blood serum, in turn, contains two agglutinins, anti-A and anti-B. Four blood groups have been distinguished: Group I: possesses neither agglutinogen but possesses both agglutinins; it is group O or the group of universal donors; Group II: is group A, provided with agglutinogen A and agglutinin anti-B; Group III: possesses agglutinogen B and agglutinin anti-A; Group IV: (AB) which contains both agglutinogens and lacks agglutinins; it is the group of universal recipients. When a blood containing a certain agglutinogen is brought into contact with another blood containing the corresponding agglutinin, the phenomenon of iso-agglutination occurs: the red blood cells agglutinate and under the microscope irregular clumps of them are observed. In practice, the blood group test is performed by means of test sera. The individual blood group is a constant, congenital, hereditary characteristic passed on from the parents according to Mendelian laws. It undergoes no qualitative alteration during life; at birth there is an incomplete quantitative development of the agglutinins, which possess a receptive strength of about one quarter to one eighth of that of an adult; this strength increases until it reaches its maximum between the ages of 15 and 20 and remains so until old age. For this reason there may be errors in determining the blood group in newborns and infants.
Important is the knowledge of the following laws: 1) the properties A and B are dominant characters with respect to O, so that they are found in children only when they are also present in the parents; however, even if present in the parents, they may not appear in the children; the property O, on the other hand, which is recessive, may be found in children even if it does not manifest itself 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 brought to light new agglutinogens, in addition to A and B, to which no preformed agglutinins correspond in the blood of other individuals; these are the blood groups respectively called M, N, MN. Later the agglutinogen P was also discovered and in 1940 Landsteiner and Wiener found the agglutinogen Rh, present in about 85% of humans, who are thus classified as Rh-positive, while the remaining 15% belong to the Rh-negative group. From this knowledge two further laws have emerged: 1) the properties M and N are dominant and cannot appear in children if the parents lack them; 2) the properties M and N are allelomorphic properties: for this reason the property M (without N) or the property N (without M) must appear in the children if they are present singly in the parents, provided they are in a pure state. By researching the blood groups present in the blood of the mother, the child, and the presumed father and comparing them with the data in special tables, it is possible to arrive at the exclusion of paternity. In practice, compatibility of blood group is not given the value of a real relationship of filiation, whereas, on the contrary, in cases of incompatibility the exclusion of the presumed father can be established with certainty.
In recent times further research has been carried out on group-specific systems, especially by foreign authors. Various subgroups of A have been studied, namely A1, A2, A3, etc., and importance has been given not only to their qualitative but also to their quantitative aspects; likewise importance has been given to the notable rarity of the subtypes A3, A4, A5, M2, N2, N3. For example, the presence of an A4 in the presumed father and in the child, which is found with a probability of one in a million, has led Hirszfeld and Ansel to consider paternity established. Similarly, importance has been given to the rarity of certain genotypes of the Rh system, the rarity of the Lewis, Kell, and Cellano factors, etc.
Research has also been carried out in Italy and is still in progress, although limited by the difficulty of procuring the necessary sera. According to recent research, the current probabilities of excluding paternity in the different mother-child combinations, for Italians, reach up to 90.8% for the principal properties A B O, MN, Rh. Greater probabilities are obtained if the investigation is extended to the P system, to N, and to the main Rh subtypes.
It cannot therefore be denied that these group-specific researches are of importance in resolving, from a biological standpoint, the much-debated problem of researching paternity.
Maria De Arcangela