We have here a result that has very important bearings upon the value to the race of the large family and of the danger of the small family. The small family of one, two, or three children contributes on the average much more than its share of pathological and defective persons. No matter just now what the causes are, they seem to be more or less beyond remedy. The result for the future, however, must be reckoned with. This relation has important bearings upon the custom of primogeniture as well as upon the eugenic values of the large family. In conclusion let us give a few sentences only slightly modified from Pearson's "Grammar of Science." The subject of differential fertility is not only vitally important for the theory of evolution, but it is crucial for the stability of civilized societies. If the type of maximum fertility is not identical with the type fittest to survive in a given environment, then only intensive selection can keep the community stable. If natural selection be suspended there results a progressive change; the most fertile, whoever they are, tend to multiply at an increasing rate. In our modern societies natural selection has been to some extent suspended; what test have we then of the identity of the most fertile and the most fit? It wants but very few generations to carry the type from the fit to the unfit. The aristocracy of the intellectual and artizan classes are not equally fertile with the mediocre and least valuable portions of those classes and of society as a whole. Hence if the professional and intellectual classes are to be maintained in due proportions they must be recruited from below. This is much more serious than would appear at first sight. The upper middle class is the backbone of a nation, supplying its thinkers, leaders, and organizers. This class is not a mushroom growth, but the result of a long process of selecting the abler and fitter members of society. The middle classes produce relatively to the working classes a vastly greater proportion of ability; _it is not want of education, it is the want of stock which is at the basis of this difference_. A healthy society would have its maximum of fertility in this class and recruit the artizan class from the middle class rather than _vice versa_. But what do we actually find? A growing decrease in the birth rate of the middle and upper classes; a strong movement for restraint of fertility, and limitation of the family, touching only the intellectual classes and the aristocracy of the hand workers! Restraint and limitation may be most social and at the same time most eugenic if they begin in the first place to check the fertility of the unfit; but if they start at the wrong end of society they are worse than useless, they are nationally disastrous in their effects. The dearth of ability at a time of crisis is the worst ill that can happen to a people. Sitting quietly at home, a nation may degenerate and collapse, simply because it has given full