THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 295 



in which we are using these terms. Thus the classification of selection by J. Mark 

 Baldwin includes a number of processes which belong to ontogeny only. 



The processes which belong strictly to selection are the following: 



Human, or artificial selection. 



Natural selection, survival of the fittest. 



Elimination, destruction of the unfit. 



Cessation of selection, panmixia. 



Coincident or organic selection in part. 



Sexual selection, the choice of mates. 



The "germinal selection" of Weismann simply expresses the fact that natural 

 selection acts upon the ontogenic and environmental reactions, predispositions 

 and potentialities of heredity. 



The following citations from Castle's recent work 1 afford a concrete illustra- 

 tion of the potency idea: 



"... But there occur also cases in which the varying gametic potency is associated directly 

 with the character affected. One such I was able to describe in 1906 — that of an extra toe in guinea- 

 pigs. It was found while building up a polydactylous race by selection and crossing with other races 

 that individuals varied in the potency which the character had in their gametes. In general the 

 better developed the character was in an individual the more strongly was it transmitted, i. e., the 

 larger was the proportion of polydactylous individuals produced in crosses. In no case, however, was 

 this a recognizable Mendelian proportion, though both dominance and segregation seemed to be 

 taking place. Variation in potency was, however, unmistakable and was transmitted from generation 

 to generation." 8 See Fig. 36 (pp. 100-101). 



"Great as has been the contribution of Mendelian principles to our knowledge of heredity, they 

 do not reduce the whole art of breeding to the production of new combinations of unit characters 

 through crossing. Selection is required also, not merely among different combinations of unit-charac- 

 ters, but also among individuals representing the same combinations selection is required of those 

 possessing the desired characters in greatest potency" (pp. 104-105). 



"From the evidence in hand we conclude that Darwin was right in assigning great importance 

 to selection in evolution; that progress results not merely from sorting out particular combinations 

 of large and striking unit-characters, but also from the selection of slight differences in the potentiality 

 of gametes representing the same unit-character combinations. It is possible to ascribe such differences 

 to little units additional to the recognized larger ones, but if such little units exist, they are indeed 

 very little as well as numerous, and by adding to the effect of the larger ones they produce what amount* 

 to modification of them" (pp. 126-127). 



Coincident Selection. 



T?he term " coincident selection," suggested by Lloyd Morgan, seems to be 

 more expressive of the principle than the term "organic selection" proposed by 

 Baldwin for the Baldwin-Morgan-Osborn hypothesis. As this is one of the illus- 

 trations of the law of the inseparable factors it is treated below (p. 302). 



Baldwin 3 offers the following definition of cessation of selection, or panmixia : 



"Panmixia [Gr. ira* all, + >u£«, a mixing]: Ger. panmixie; Fr. panmizie; Ital. panmissia. 

 Promiscuous interbreeding within the limits of a species or other group as contrasted with breeding 



8vo. D. Appleton 



under artificial selection or other form of isolation. 



1 Castle, Wm , m 



& Co., 1911, 184 pp.' 



* An alternative explanation is possible, viz., that the development of the fourth toe depends 

 upon the inheritance of several independent factors, and that the more of these there are present, the 

 better will the structure be developed. The correctness of such an interpretation must be tested by 

 further investigations. 



* Baldwin, J. Mark, Dictionary of Philosophy and Psychology, vol. II, The Macmillan Company, 

 1902, pp, 255-256. 



