Page:Scientia - Vol. X.djvu/124

116 one may be taken as a valid and reliable criterion of the other. Many cases like that just cited might be given from existing Mendelian literature. Indeed, it may be said that nearly all experiments in crossing plants or animals furnish illustrations of the general principle that the somatic condition of a character is a most unreliable criterion of its probable behavior in inheritance.

It may be objected that the type of cases cited in the preceding paragraph are hardly a fair basis for the criticism of the « law of ancestral inheritance » in regard to the logical foundation of the procedure by which it is deduced, since the illustrations mentioned concern themselves with qualitative variations, whereas it is with quantitative variations that the biometrical study of inheritance has had to do. As a matter of fact the case for the « law » is made no better if this contention be granted, though it is difficult to see what reason exists for supposing that so-called qualitative variations are not inherited in fundamentally the same way as are so-called quantitative variations. Every character and every variation has both a qualitative and a quantitative aspect. But if we consider only the quantitative aspect of the matter, as has been done in much of the biometric work on inheritance, the same principle of the unreliability of somatic conditions as a criterion of hereditary behavior comes clearly forth from the work of Johannsen on beans, that of Jennings on Paramecium and in unpublished data regarding the inheritance of fecundity in the domestic fowl. Thus, we may have the inbred descendants of one hen A with a high winter egg production record (say 62 eggs) all uniformly showing in succeeding generations a high degree of winter productiveness, approximately the same as that of the original bird (60-65 eggs). At the same time we may have another bird B with a winter record precisely like that of A (62 eggs again) whose inbred descendants, through three generations at least, all uniformly show a mediocre or low degree of winter productiveness (ave-