Many childless marriages are rendered not only happy but very useful to society by the adoption of children. It should always be remembered that from the standpoint not only of family life but of old age and of society in general, children are the most important result of marriage.
The worst forms of unfitness for marriage are hereditary, but some hereditary defects are mild, some terrible. There is much doubt as to whether many defects are hereditary or are the result of unfavorable conditions during pregnancy and early infancy. Far too much emphasis is placed upon external and easily visible defects in comparison with internal ones which cannot be so readily detected. Such minor hereditary defects as hare lip or misshaped fingers do not necessarily indicate unfitness for marriage. They are far less dangerous than hereditary susceptibility to diseases such as diabetes or weakness of the heart, which lead to unhappy marriages by reason of frequent illness or early death. A hereditary tendency toward short-sightedness or defective teeth, on the contrary, may permit the longest and happiest of marriages. All inherited defects are regrettable, but practically no one is free from them in some minor form.
The sensible attitude toward minor hereditary defects is to balance their real importance against both the good and the bad qualities shown not only by the individual but by his brothers, sisters, parents, and other relatives. Conscientious sufferers from visible defects of any kind are apt to overestimate their importance. Moreover, many supposedly hereditary defects may equally well be the result of an unfavorable environment like that which caused similar defects in the parents. Under ideal conditions they might never appear at all. In such matters, too, the best course is to consult a good physician. Often, perhaps usually, the best thing is merely to avoid marriage with a person showing defects like one's own, and then strive to give your children so good an environment that only the best in them will have a chance to develop. Fortunately the vast majority of people inherit a fairly good assemblage of traits which balance in such a way as to produce normal human beings.
One type of deficiency, however, renders people genuinely unfit for marriage. It takes various forms. One form, easily recognized, is what is commonly called "mental deficiency." By this we mean not merely the kind of mind found in idiots and imbeciles, but that which appears in morons and other "high grade" mental weaklings. Such mental weakness, or feeble-mindedness, is especially dangerous to society because it often afflicts people who are physically strong and attractive, and who are eager to marry. When such persons marry, they exercise little self-control and are likely to have large families. In this respect they are unlike mental defectives of lower types, who rarely have many children and whose children are likely to die young. "High grade" mental defectives tend to marry one another. The result is bad in two ways. First, if the mental deficiency of one or both parents is hereditary, as is often the case, children with defective mental capacity are sure to be born, and will in turn produce other defectives. Second, even if the defects of the parents are due to accident or disease, the children are almost sure to be badly brought up.
The chief type of mental weakness is emotional in nature. Here is a young fellow who as a boy was always a cry-baby and mamma's darling. He is afraid to stand up for himself, afraid of athletics, afraid of girls; and, because of all this, he is lonely, morose, and secretive. Here is a girl of great ability and charm but subject to fits of deep depression. Another young man loses his temper very easily and cherishes resentment for a long time over trivial matters. The girl whom he is interested in is extremely self-conscious and thinks that she is being purposely slighted unless she is the center of everything. Others, both boys and girls, are excessively irritable, very suspicious, inordinately selfish, hysterical, vainglorious, or in other ways show lack of self-control and emotional stability. Later in life such conditions may lead to intense misery. Nevertheless traits of this sort are often combined with very fine qualities in other respects. This renders it extremely hard to decide whether such persons are fit for marriage.
It is extremely difficult to determine whether emotional instability, selfishness, and other undesirable traits are due to heredity or environment. At this point we enter a field of great difficulty because a trait may be inborn, but not hereditary. A child may be born with serious handicaps because some ailment due to unfavorable environment prevented its mother from nourishing it properly before it was born. Such weakness is not truly hereditary. It will not appear in later generations unless the mothers of those generations also suffer from environmental conditions similar to those which prevented the first mother from nourishing her child. It often happens that such conditions are repeated from generation to generation. If this happens very early in the pre-natal life of the child, the results are very likely to be misinterpreted as hereditary.
In the last few decades the study of heredity has been so fascinating and fruitful that biologists have given comparatively little attention to early environmental influences. Recent work, however, suggests that such influences are far from negligible. My own studies of season of birth illustrate the matter. They suggest that the effect of physical environment upon the health of the parents before a child is conceived has an important effect upon the child's future health and achievement.
Only a hint of the chain of evidence leading to this conclusion is here possible. Many investigations of deaths, fatigue, work, and disease, as well as numerous carefully controlled laboratory experiments, indicate that people feel most comfortable and vigorous, and have the best health, when the average temperature for night and day together is about 63°. Nothing is more pleasant than a day of this optimum kind in May or June. At midday the thermometer rises to 70° more or less; at night it falls low enough so that people sleep soundly and restfully.
A study of season of birth in many countries indicates that children who are conceived when optimum weather of this kind arrives in the spring have stronger constitutions and greater powers of application than do those conceived at any other season. Evidence of constitutional vigor is found in length of life. In four large groups of Americans and in one of Italians it has been found that those born in March, and therefore conceived in June at the time of optimum weather, live longer than those born at other seasons. Among 39,000 people who were born in the eastern United States and who lived beyond the age of two years I found that on an average those born in March lived 3.8 years longer than those born from July to September.
Other evidence, into which we cannot go, suggests that man, like other animals, inherits a definite seasonal cycle of reproduction. As the temperature rises toward the optimum in the spring the functions of the body change in such a way that not only is there a pronounced feeling of well-being, but the children conceived at that time have more than the average vigor, and hence correspondingly long life.