The Good Housekeeping Marriage Book. Various
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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.
The evidence that these children have greater powers of application, or at least that some of them do, lies in the birthdays of eminent people in countries as diverse as India, Spain, Russia, England, France, Germany, Sweden, and the United States. In all these countries the percentage of eminent people conceived when the optimum weather prevails rises much higher than does the corresponding percentage among ordinary people. Moreover, the greater the degree of eminence, the more marked is the contrast with people as a whole.
The reason for this condition must be that the vigor which gives to many people long life gives to highly gifted people a sort of power of steady application and hard work—an emotional stability—which enables them to use their faculties to the best advantage. Thus they achieve fame in greater measure than do equally well-endowed persons with less vigor. There is not the slightest reason to suppose that children conceived at one season of the year inherit any better minds than do their brothers and sisters conceived at other seasons. There is equally little reason to believe that the average inheritance of mental ability declines as the period of conception approaches midwinter, the low point in the seasonal cycle of reproduction. On the other hand, length of life furnishes evidence that physical vigor varies according to the degree to which the mothers at least, at the time of a child's conception, have been under the influence of environmental conditions which assist the germ cells in developing into vigorous babies. Many studies of eminent people show that they are uncommonly long-lived. When deaths in war and by accident are omitted, the average length of life of 11,000 people in the British Dictionary of National Biography was 71 years. Eminence and the kind of constitutional vigor that leads to long life go together.
This brings us back to the problem of fitness for marriage. If the effect of the weather on the vigor of parents can have such an influence on health, longevity and achievement, such conditions as diet and mode of life may produce similar effects. This possibility adds still greater interest to the two-edged bearing of what we have just been saying upon the problem of fitness for marriage. In the first place it appears that an unexpected number of weaknesses which are sometimes considered hereditary are environmental. Nevertheless, they are also inborn and cannot easily be eradicated by education. Therefore the chance that ordinary normal people carry a dangerous heredity is reduced, but the responsibility of parents to see that their children are properly born is increased. In the second place, it becomes more evident than ever that fitness for marriage implies intelligent willingness and persistence in acting upon the discoveries of science in whatever way may be best for the unborn child. We have long insisted upon the right environment for the expectant mother during pregnancy. The new discoveries suggest that we must insist equally upon the right environment and manner of life before pregnancy begins.
This brings up a very interesting question upon which biologists are not agreed. Does what has just been said about the period before pregnancy apply to the father as well as the mother? Many biologists doubt whether we have any proof that environmental influence can weaken the sperm cells of the male in such a way that the offspring are thereby weakened. Other biologists, such as Professor Pearl, of Johns Hopkins University, and Professor C. A. Mills, of Cincinnati, have made some interesting experiments which lead them to believe that sperm cells weakened by environmental conditions may affect the vitality of the developing offspring. In short, at the present time there is no agreement among competent scientific men that the health and mode of life of the father, as well as of the mother, influence the physical well-being of the developing child, and thereby affect its emotional stability and other qualities. Until this question is scientifically settled it is obvious that the men best fitted for marriage and parenthood are those who act in such a way that they cannot harm their children no matter which view is correct.
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