Heredity

HEREDITY. - Transmission from parents to children of the characteristics proper to the species, the race, the individual.

This transmission takes place through the sexual cells, and is governed by complex laws, the study of which is the object of a particular science: genetics.

The carriers and determinants of hereditary characteristics are considered to be the genes, tiny protoplasmic particles aligned in the chromosomes contained in the cell nucleus: in some cases genes have also been located in the protoplasm (plasmagenes).

Every individual carries within himself a double complement of genes: one of paternal origin and one of maternal origin. If a given hereditary characteristic (e.g., color of the iris) is the same in both parents, it also appears in the child: if instead it is different in the two parents, then one of the two appears in the child (dominant characteristic) while the other does not manifest itself, but persists, in a latent state, in the individual (recessive characteristic) and may appear, under certain circumstances, in his descendants. Hence the distinction between homozygous, an individual who carries in his hereditary complement, in the pure state, only the characteristic that has manifested itself in him, and heterozygous, an individual who, while manifesting a given characteristic, in reality carries within himself, in a latent state, the opposite, recessive characteristic.

It should be noted, however, that often a characteristic is conditioned by several genes located in different chromosomes, and that therefore, given the various possible combinations among these, a whole range of intermediate characteristics may appear in the individual (e.g., color of the hair).

In the descendants of two heterozygotes it may happen that, through the meeting, at the moment of fertilization, of the paternal and maternal genes carrying the recessive characteristic, an individual is born in whom there appears that characteristic which was instead not evident in his parents.

Heredity refers both to physiological characteristics, which cause the child to be similar to his parents, and to pathological characteristics.

As regards pathological heredity, it is first necessary to clarify the frequent misunderstanding that is made between hereditary diseases and congenital diseases. A hereditary disease is that disease which is conditioned by a gene: it must therefore be considered as a true hereditary characteristic already present in one or both of the seminal cells from which the individual originated: it can therefore come from either the mother or the father, and it is something ineluctable, which one is not able to modify. A congenital disease is instead a disease that is contracted in intrauterine life, through contagion from the mother to the fetus. Consequently it is not a hereditary characteristic linked to genes, it can come only from the mother and not from the father (from the latter only indirectly, through contagion of the mother), and finally it is not something fatal and unmodifiable, but can be avoided and treated like any other disease.

It is therefore clear that an infectious disease can be congenital but never hereditary, and that it is wrongly spoken of, for example, of hereditary syphilis, since this in reality is transmitted congenitally from the diseased mother to the fetus.

True hereditary diseases have a common characteristic: they lack that dynamism which is proper to all other diseases, even non-infectious ones, and which causes the morbid process to tend to evolve toward recovery or toward death. Hereditary diseases are instead static and, more than true diseases, must in reality be considered as affections or malformations, whether morphological or functional. They constitute a locus minoris resistentiae of the organism which causes other causes or other diseases at a given moment to break a laborious biological equilibrium and to bring the individual affected by them to disastrous consequences. For example, a hemophiliac (an individual in whom the blood is incapable of clotting) can, despite his hemophilia, live to an advanced age as a perfectly normal individual. If, however, at a certain moment a trauma intervenes that causes a hemorrhage, even of no serious extent, he may meet, through loss of blood, the most disastrous consequences.

Among the best-known or most widespread hereditary diseases we shall recall skeletal malformations (hexadactyly, syndactyly, etc.), hemophilia, color blindness (inability to distinguish certain colors), albinism (absence of pigmentation), certain forms of deafness and blindness, some defects of the heart and of the circulatory system, Cooley's disease (a form of progressive anemia connected with skeletal malformations), certain other blood diseases, etc. The so-called "lethal factor" has also been observed, at least in certain animals, which makes life impossible for the individual, even though he may sometimes appear normal.

In addition to these various clearly evident pathological characteristics, others, less conspicuous, may be inherited, which consist in a deficiency of resistance or of functionality and in an exaggerated reactivity of a given system, organ or tissue, such as to predispose to a given disease or group of diseases (heredity of certain constitutions, of certain nervous diseases of a degenerative character, etc.).

In general, hereditary pathological characteristics behave as recessive characteristics and manifest themselves only when they meet in the descendants of two parents both carrying that characteristic. Consequently one understands why hereditary diseases appear with greater frequency in the descendants of blood relatives who, coming from the same stock, can more easily carry within themselves, in the recessive state, the same pathological characteristic (degeneration of certain lineages in which unions between blood relatives are frequent).

In some cases (hemophilia) the pathological characteristic is linked to sex, inasmuch as the gene that determines it is located in the so-called sex chromosome, that is, the one that also carries the genes conditioning the sexual characteristics.

Hereditary diseases, unlike congenital ones, are not curable: they can only be prevented by avoiding marriages between persons carrying the morbid characteristic, even if only in the recessive state (v. EUGENICA).

Brenno Babudieri

MORAL THEOLOGY AND PASTORAL

Once the possibility of an influence of h. on human activity and consequently on the morality of the act is admitted, two excesses are to be avoided.

We cannot, with the Italian anthropological school, conceive of h. as an indestructible chain of effect and causes, whereby our personality is linked back to the ultimate origin of things through the indefinite concatenation of necessities (T. A. Riboli). And still less can we accept the teachings of the positive school of C. Lombroso, which draws the ultimate consequences, annulling under the iron law of h. any semblance of human freedom. But neither must we fall into the opposite error of the classical school, which considers the will of men in perfect indifference among the many inclinations, including the hereditary ones.

The truth lies in the middle. First of all, hereditary inclinations and tendencies of a moral order (and it is with these that we are chiefly concerned) can be not only degenerative but also regenerative. To this latter category belongs that patrimony of inclinations to goodness and honesty, of horror of vice, which forms the wealth of many Christian generations. In degenerative tendencies, then, there can indeed occur extreme cases, in which the weight of hereditary tendencies is such and so great as to render the individual completely tainted and utterly irresponsible; but ordinarily hereditary tendencies, more or less strong, are not impregnable and, duly checked and contained, especially by removing the patient from the environment, from bad influences and occasions, can be controlled and watched over, and at times even annulled in their perniciousness. We must nevertheless take them into account especially when it is a question of the choice of a state that commits us for a whole lifetime. And in the external forum the judge must take them into account in judging the imputability of the crime (can. 3199).

The problem of hereditary tendencies perhaps also gives us the explanation of certain wise provisions, relating to certain irregularities and to specific impediments that are found introduced into ecclesiastical legislation, long before so much scientific knowledge on the matter had matured.

Such is the case, for example, of illegitimate persons (can. 984, 1°) who are considered irregular in relation to the Sacrament of Order; of neophytes (can. 987, 6°) who cannot be admitted thereto until, in the judgment of the Ordinary, they are sufficiently formed (can. 987, 6°). And perhaps the same reason can also be found, together with others, at the basis of the matrimonial impediment of consanguinity (can. 1076).

Furthermore, the problem of h. enters into the solution of many moral questions; thus in the theory and practice of eugenics (v.), both positive and negative, with which the practice of sterilization (v.) is also connected; in preparation for marriage and especially in the prenuptial examination.

Only by keeping well in mind not solely scientific theories but also the hierarchy of human values will it be possible to give these problems a just solution.

Pietro Palazzini