No. 544] 



OBIGIN OF UNIT CHARACTERS 



199 



The idea that the positive or present character domi- 

 nates over the negative, latent or absent character has 

 become the prevailing one. 



It seems highly probable, observes Davenport (1910), that the fu- 

 ture will show that many more advanced or progressive conditions are 

 really due to one or more unit-characters not present in the less ad- 

 vanced condition. In that case it will appear that there is a perfect 

 accord in the two statements that the progressive and the " present " 

 factor are dominant (pp. 89-90) ... the specific characteristics are 

 mostly those that appear late in ontogeny (p. 86) ... the potency 

 of a character may be defined as the capacity of its germinal deter- 

 miner to complete its entire ontogeny. If we think of every character 

 as being represented in the germ by a determiner, then we must recog- 

 nize the fact that this determiner may sometimes develop fully, some- 

 times imperfectly and sometimes not at all [italics our own]. . . . 

 When such a failure occurs in such a normal strain a sport results. 

 . . . Potency is variable. Even in a pure strain a determiner does 

 not always develop fully and this is an important cause of individual 

 variability (Davenport, 1910, p. 92). 



Plate similarly favors the hypothesis of dominance of 

 newer or progressive characters. He observes (1910) : 



The [Mendelian] laws of inheritance favor progressive evolution in 

 two ways, for . . . higher, more complicated characters are generally 

 dominant to the lower, and . . . qualitative characters usually follow 

 the Mendelian principle in the case of closely related forms (races, 

 varieties) while in the crossing of species they follow intermediate [or 

 blended] inheritance as a rule. In the latter case there is the possibility 

 that the crossing may have a swamping effect, but this can play no 

 large role on account of the infrequency of hybrids between species 

 (Plate, 1910, p. 606). 



The same author is of the opinion that phyletic evolu- 

 tion is discontinuous as regards the transformations of 

 the determinants [determiners], but in most cases is con- 

 tinuous in their visible outward workings. He thus main- 

 tains that while germinal transformations are discon- 

 tinuous there may be no real antithesis between con- 

 tinuous and discontinuous somatic variation. 



Thus Mendelians appear to agree, first, that there are 

 grades of continuity and discontinuity, that there are 

 antithetic characters which are sharply discontinuous, 

 others which are partly continuous, blended or intermedi- 



