This transmission occurs through the sexual cells and is governed by complex laws, the study of which is the subject of a particular science: genetics.
The genes are considered to be the carriers and determinants of hereditary characteristics; these are minute protoplasmic particles aligned in the chromosomes contained within the cell nucleus. In some cases, genes have also been localized in the protoplasm (plasmagenes).
Every individual carries within themselves a double set of genes: one of paternal origin and one of maternal origin. If a given hereditary characteristic (e.g., eye color) is the same in both parents, it will also appear in the child. If, however, it differs in the two parents, then one of the two characteristics will appear in the child (dominant characteristic), while the other will not manifest itself but will persist in a latent state within the individual (recessive characteristic) and may appear under certain circumstances in their descendants. Hence the distinction between homozygote—an individual who carries in their hereditary makeup, in a pure state, only the characteristic that has manifested itself—and heterozygote—an individual who, while manifesting a given characteristic, actually carries within themselves, in a latent state, the opposite, recessive characteristic.
It should be noted, however, that often a characteristic is conditioned by multiple genes located on different chromosomes, and that, given the various possible combinations among these, the individual may exhibit a whole range of intermediate characteristics (e.g., hair color).
In the descendants of two heterozygotes, it can happen that, at the moment of fertilization, the meeting of paternal and maternal genes carrying the recessive characteristic results in the birth of an individual in whom that characteristic appears, even though it was not evident in the parents.
**ERCOLANO, St.** – Church of St. E. (1307–1326) – Perugia, 16.
The term refers both to physiological characteristics, which ensure that a child resembles their parents, and to pathological characteristics.
With regard to pathological heredity, it is first necessary to clarify the frequent confusion between hereditary diseases and congenital diseases. A hereditary disease is one that is conditioned by a gene; it must therefore be regarded as a true hereditary characteristic already present in one or both of the germ cells from which the individual is derived. It can therefore come from either the mother or the father and is something ineluctable that cannot be altered. A congenital disease, on the other hand, is one that is contracted during intrauterine life through contagion from the mother to the fetus. Consequently, it is not a hereditary characteristic linked to genes, can only come from the mother and not from the father (except indirectly through the mother’s contagion), and is not something fatal and unchangeable but can be prevented and treated like any other disease.
It is therefore clear that an infectious disease can be congenital but never hereditary, and that it is an abuse of language to speak, for example, of hereditary syphilis, since this is in fact transmitted congenitally from the infected mother to the fetus.
True hereditary diseases have a common characteristic: they lack the dynamism that is proper to all other diseases, even non-infectious ones, and that causes the morbid process to evolve toward either recovery or death. Hereditary diseases are instead static and, more than true diseases, should in fact be considered as malformations—both morphological and functional. They constitute a locus minoris resistentiae of the organism, which means that at a given moment other causes or diseases may disrupt a precarious biological equilibrium and lead the individual affected by them to fatal consequences. For example, a hemophiliac (an individual whose blood is incapable of clotting) may, despite their hemophilia, live to an advanced age as a perfectly normal individual. If, however, at a certain point a trauma occurs that causes even a minor hemorrhage, they may succumb, through exsanguination, to the most dire consequences.
Among the most well-known or widespread hereditary diseases, we may mention skeletal malformations (exostoses, syndactyly, etc.), hemophilia, color blindness (inability to distinguish certain colors), albinism (absence of pigmentation), certain forms of deafness and blindness, some heart defects and circulatory system disorders, Cooley’s disease (a form of progressive anemia associated with skeletal malformations), some other blood diseases, etc. It has been observed, at least in certain animals, the so-called “lethal factor,” which makes life impossible for the individual, even if they sometimes appear normal.
In addition to these various clearly evident pathological characteristics, others, less conspicuous, may also be inherited; these consist of a deficiency in resistance or functionality or an exaggerated receptivity of a given system, organ, or tissue, predisposing the individual to a particular disease or group of diseases (heredity of certain constitutions, of certain degenerative nervous diseases, etc.).
In general, pathological hereditary characteristics behave like recessive characteristics and manifest themselves only when they are combined in the descendants of two parents who both carry that characteristic. It is therefore understandable why hereditary diseases appear more frequently in the descendants of consanguineous parents, who, deriving from the same lineage, are more likely to carry the same pathological characteristic in a recessive state (degeneration of certain lineages in which unions between relatives are frequent).
In some cases (hemophilia), the pathological characteristic is linked to sex, inasmuch as the gene that determines it is located on the so-called sex chromosome, which also carries the genes conditioning sexual characteristics.
Unlike congenital diseases, hereditary diseases are not curable; they can only be prevented by avoiding marriages between individuals who carry the morbid characteristic, even if only in a recessive state (v. EUGENICS).
**Moral and pastoral considerations.** – Given the possibility of heredity influencing human activity and, consequently, the morality of an act, two extremes must be avoided.
We cannot, with the Italian anthropological school, conceive of heredity as an indestructible chain of cause-and-effect, whereby our personality is linked to the ultimate origin of things through a defined chain of necessities (T. A. Ribot). Nor can we accept the teachings of C. Lombroso’s positivist school, which goes to the extreme of annihilating any semblance of human freedom under the iron law of heredity. But neither should we fall into the opposite error of the classical school, which considers the will of human beings to be in perfect indifference among the many inclinations, including hereditary ones.
Truth lies in the middle. First of all, the inherited moral inclinations and tendencies (and it is these that we are chiefly concerned with) may be not only degenerative but also regenerative. To this latter category belongs that patrimony of inclinations toward goodness and honesty, of horror toward vice, which forms the wealth of many Christian generations. In the case of degenerative tendencies, on the other hand, extreme cases may occur in which the weight of hereditary tendencies is so great as to render the individual completely irresponsible; ordinarily, however, hereditary tendencies—more or less strong—are not insurmountable, and, if properly checked and contained—especially by removing the patient from the environment, from bad influences and occasions—can be controlled and monitored, and sometimes even neutralized in their harmfulness. We must nonetheless take them into account, especially when it comes to choosing a state of life that will commit us for an entire lifetime. And in the external forum, the judge must take them into account in assessing the imputability of a crime (can. 2199).
The problem of hereditary tendencies may perhaps also explain some wise provisions, relating to certain irregularities and specific impediments found in ecclesiastical legislation, long before so much scientific knowledge on the subject had matured.
This is the case, for example, of illegitimate children (can. 984, 19), who are considered irregular with regard to the Sacrament of Holy Orders; of neophytes (can. 987, 69), who cannot be admitted to it until, in the judgment of the Ordinary, they have been sufficiently formed (can. 987, 69). And perhaps the same motive, along with others, may be found at the root of the impediment to marriage arising from consanguinity (can. 1076).
Furthermore, the problem of heredity enters into the solution of many moral questions; thus in the theory and practice of eugenics (v. 3), both positive and negative, with which the practice of sterilization (v.) is also connected, as well as in preparation for marriage and especially in the pre-nuptial examination.
Only by keeping in mind, not only scientific theories, but also the hierarchy of human values, can a just solution be given to this problem.
HEREDITY — AUGUSTINIAN HERMITS
1947–48. — For recent studies on the inheritance of human Puglian traits, V. Franz, L'eredità nella patologia e nella clinica, Bologna 1942. Pietro Palazzini