_Economy of Effort._—I shall now use the table to show the economy of concentrating our attention upon the highest classes. We will therefore trace the origin of the V class—which is the highest in the table. Of its 34 or 35 sons, 6 come from V parentages, 10 from U, 10 from T, 5 from S, 3 from R, and none from any class below R. But the numbers of the contributing parentages have also to be taken into account. When this is done, we see that the lower classes make their scores owing to their quantity and not to their quality; for while 35 V-class parents suffice to produce 6 sons of the V class, it takes 2500 R-class fathers to produce 3 of them. Consequently the richness in produce of V-class parentages is to that of the R-class in an inverse ratio, or as 143 to 1. Similarly, the richness in produce of V-class children from parentages of the classes U, T, S, respectively, is as 3, 11–1/2, and 55, to 1. Moreover, nearly one-half of the produce of V-class parentages are V or U taken together, and nearly three-quarters of them are either V, U or T. If then we desire to increase the output of V-class offspring, by far the most profitable parents to work upon would be those of the V-class, and in a threefold less degree those of the U class. When both parents are of the V class the quality of parentages is greatly superior to those in which only one parent is a V. In that case the regression of the genetic centre goes twice as far back towards mediocrity, and the spread of the distribution among filials becomes nine-tenths of that among the parents, instead of being only three-quarters. The effect is shown in table IV. There is a difference of fully two divisions in the position of the genetic centre, that of the single V parentage being only a trifle nearer mediocrity than that of the double T. Hence it would be bad economy to spend much effort in furthering marriages with a higher class on only one side. TABLE IV.—_Distribution of sons. (1) One parent of class V., the other unknown. (2) Both parents of class V (from Table II., with decimal point and an 0)._ ───────────────────────────────────────────────────────────────────── Distribution of Sons ──────────────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬────── │ _t_ │ _s_ │ _r_ │ R │ S │ T │ U │ V │ Total ──────────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼────── One V-parent │ 0·3│ 1·2│ 3·5│ 7·9│ 9·6│ 7·5│ 3·6│ 1·3│ 34·3 Two V-parents │ │ │ │ 3·0│ 5·0│ 10·0│ 10·0│ 6·0│ 34·0 ──────────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴────── Position of the filial centre of (1) = 1·44, of (2) = 2·89. When both parents are T it = 1·58.