Introduction to the Science of Sociology

by Robert Ezra Park; E. W. Burgess

We may now consider briefly the inheritance of certain pathological or abnormal states, to see in how far the foregoing principles hold for them also. Sometimes the abnormal condition is positive, due to a new trait; but sometimes, on the contrary, the normal condition is the positive one and the trait is due to a defect.

Deaf-mutism is due to a defect; but the nature of the defect is different in different cases. Deaf-mutism is so varied that frequently two unrelated deaf mutes may have hearing children. But if the deaf-mute parents are cousins, the chances that the deafness is due to the same unit defect are increased and all of the children will probably be deaf.

From the studies of Dr. Goddard and others, it appears that when both parents are feeble-minded all of the children will be so likewise; this conclusion has been tested again and again. But if one of the parents be normal and of normal ancestry, all of the children may be normal; whereas, if the normal person have defective germ cells, half of his progeny by a feeble-minded woman will be defective.

Many criminals, especially those who offend against the person, are feeble-minded, as is shown by the way they occur in fraternities with feeble-mindedness, or have feeble-minded parents. The test of the mental condition of relatives is one that may well be applied by judges in deciding upon the responsibility of an aggressor.

Not only the condition of imperfect mental development, but also that of inability to withstand stress upon the nervous system, may be inherited. From the studies of Dr. Rosanoff and his collaborators, it appears that if both parents be subject to manic depressive insanity or to dementia precox, all children will be neuropathic also; that if one parent be affected and come from a weak strain, half of the children are liable to go insane; and that nervous breakdowns of these types never occur if both parents be of sound stock.

Finally, a study of families with special abilities reveals a method of inheritance quite like that of nervous defect. If both parents be color artists or have a high grade of vocal ability or are littérateurs of high grade, then all of their children tend to be of high grade also. If one parent has high ability, while the other has low ability but has ancestry with high ability, part of the children will have high ability and part low. It seems like an extraordinary conclusion that high ability is inherited as though due to the absence of a determiner in the same way as feeble-mindedness and insanity are inherited. We are reminded of the poet: "Great wits to madness sure are near allied." Evidence for the relationship is given by pedigrees of men of genius that often show the combination of ability and insanity. May it not be that just that lack of control that permits "flights of the imagination" is related to the flightiness characteristic of those with mental weakness or defect?

These studies of inheritance of mental defect inevitably raise the question how to eliminate the mentally defective. This is a matter of great importance because, on the one hand, it is now coming to be recognized that mental defect is at the bottom of most of our social problems. Extreme alcoholism is usually a consequence of a mental make-up in which self-control of the appetite for liquor is lacking. Pauperism is a consequence of mental defects that make the pauper incapable of holding his own in the world's competition. Sex immorality in either sex is commonly due to a certain inability to appreciate consequences, to visualize the inevitableness of cause and effect, combined sometimes with a sex-hyperesthesia and lack of self-control. Criminality in its worst forms is similarly due to a lack of appreciation of or receptivity to moral ideas.

If we seek to know what is the origin of these defects, we must admit that it is very ancient. They are probably derived from our ape-like ancestors, in which they were normal traits. There occurs in man a strain that has not yet acquired those traits of inhibition that characterized the more highly developed civilized persons. The evidence for this is that, as far back as we go, we still trace back the black thread of defective heredity.

We have now to answer the question as to the eugenical application of the laws of inheritance of defects. First, it may be pointed out that traits due to the absence of a determiner are characterized by their usual sparseness in the pedigree, especially when the parents are normal; by the fact that they frequently appear where cousin marriages abound, because cousins tend to carry the same defects in their germ plasm, though normal themselves; by the fact that two affected parents have exclusively normal children, while two normal parents who belong to the same strain, or who both belong to strains containing the same defect, have some (about 25 per cent) defective children. But a defective married to a pure normal will have no defective offspring.

The clear eugenical rule is then this: Let abnormals marry normals without trace of the defect, and let their normal offspring marry in turn into strong strains; thus the defect may never appear again. Normals from the defective strain may marry normals of normal ancestry, but must particularly avoid consanguineous marriages.