Those who are interested in this aspect of the question will find the facts admirably set forth in Mr. Pell's book on The Law of Births and Deaths, being a study of the variation in the degree of animal fertility under the influence of environment.
He finds that the all-important factor which determines fertility is the amount of nervous energy of the organism, and that nervous energy is produced or modified by three specially influential factors, viz., Food, both quantity and quality; Climate, hot or cold—moist or dry; and, lastly, all those varied conditions which make for greater or lesser mental and physical activity.
Fertility, broadly speaking, varies in inverse proportion to the degree of nervous energy or what we may call vitality.
Conditions, therefore, which lower the general vitality below the normal produce abnormal fertility. This excessive child-bearing under present conditions still further lowers the standard of life and the health of the mother, hence a vicious circle is set up, the only escape from which will come by such consideration of the laws of health relating to work, housing, food and recreation as shall ensure the maximum of vitality to the workers. This is the true method of conception control.
There comes a point in the development of nervous energy which is productive of sterility. It is true that principles based on so many varying factors will necessarily appear to fail in individual cases. Environment with its influence on the nervous energy of the individual will be modified by the inherited tendency of that individual towards fertility or the reverse. We find, therefore, isolated cases of large families among the well-to-do and small families among those whose vitality is below the normal, but if the general principle is true we should expect to find a larger number of sterile marriages among the well-to-do than among those whose lives are more full of hardship, and this undoubtedly is the case.
This aspect of the problem is deserving of careful study. The desire for children in so many homes where every advantage could be given, may be gratified when more knowledge of how wisely to modify the environment of the rich is within our grasp.
It may be that the more simple life among those who have much will give to them the prize of children which they covet more than things which wealth can buy.
But let us return for a moment to the false expectation that children will come to all unless prevented.
The results of this assumption are really serious. They involve the training of large numbers of people in unnatural practices, which in many cases are unnecessary, even if they were desirable. They rob many families of the children who would have been the delight of their parents through middle and later life.
Moreover, it is obvious that advice which may be quite necessary in cases of ill-health or special conditions, may be fundamentally wrong to give broadcast to all individuals, for apart from the fact that when given to all it is largely unnecessary, there are other serious objections, as follows:—