386 TEE POPULAR SCIENCE MONTHLY 



heritable. We name the former stable characters, the latter unstable, or 

 fluctuating characters. New qualities are arising from generation to 

 generation through variation. These variations may similarly be classed 

 as stable variations, or mutations, and fluctuating, or unstable, varia- 

 tions. No result can be reached by breeding with reference to unstable 

 variations or qualities, for they are not inherited. Qualities belonging 

 to the unstable type can not be fixed by breeding. They are, therefore, 

 without significance in the problems of eugenics and evolution. It is 

 impossible, however, to discern whether an observed quality is of the 

 stable or unstable type until one follows its behavior in inheritance. 



Another fact of the greatest importance to remember is that there 

 is probably no such thing as inheritance of vague general resemblances, 

 but that inheritance is apparently always particular, definite, so-called 

 unit qualities being the things inherited. The character of any indi- 

 vidual is built up of a complex multitude of such unit qualities, each 

 heritable separately, and the character of an individual depends upon 

 the combination and interaction of the unit qualities that have been 

 passed down to him from his parents, grandparents and other pro- 

 genitors. 



In the light of these facts, what is the essential problem, first in 

 eugenics, then in evolution? The eugenics problem is accurately to 

 determine the desirable unit qualities, which must be of the stable type, 

 and to combine and fix them in the race by breeding, eliminating at the 

 same time the undesirable unit qualities. It is the problem of finding 

 the exact units of inheritance, and of so fixing and combining, by 

 breeding, these valuable units in the individuals of the coming genera- 

 tions that we shall have a more wholesome innate character in mankind. 

 The evolution problem is to find among the multitude of diverse human 

 traits new desirable unit qualities of the stable type, often only in their 

 beginnings, and to perpetuate these by breeding. 



The Galton-Pearson school of English students are willing to waive 

 accurate analysis of inheritance units, but the real problem will not be 

 solved until we know whether the human qualities with which we wish 

 to deal, the intellectual and moral as well as the physical, do follow the 

 Mendelian principles in inheritance, and until we have analyzed the 

 Mendelian qualities to their units. We have a notable example of 

 failure to secure permanent valuable results in attempting to breed from 

 individuals whose valued character had not been analyzed to its unit 

 qualities. At the Agricultural Experiment station in Orono, Maine, 

 many years of effort were given to securing a strain of fowl which would 

 lay an unusually large number of eggs. Mere breeding from hens 

 which laid many eggs was not found to be enough. The quality of high 

 fecundity could not be fixed in the strain. Selection had to be con- 

 tinued in each generation or reversion to the general average would 



