214 



THE AMERICAN NATURALIST 



[Vol. XLI 



difference of breeding time, difference of local habitat, and phy- 

 siological properties precluding inter-breeding. The clear dis- 

 cussions of Romanes and Gulick have rendered superfluous 

 much in recent disputes on Isolation and Evolution. 



Lately new conceptions in the theory of heredity have materi- 

 ally changed the conditions of the argument. Experiment has 

 shown that new characters may not be immediately swamped 

 by promiscuous breeding, but may on the contrary, in the fusion 

 of new and old races, predominate in full force over old characters 

 which they sometimes have the power of entirely subduing.^ 

 While this result is very suggestive, too little is as yet positively 

 known to make an extended discussion at all profitable. Those 

 who are inclined to argue the matter may well take caution from 

 Davenport's opinion on the integrity of unit characters. "While 

 admitting, thus, the reality of unit characters, the further study 

 of the evidence of liybridization in poultry has led me away from 

 the conception that they are rigid and ininuitiil)]e as atoms are, 

 which may l)e combined and recombined in various ways and 

 always come out of the process in their j)ristine ])urity. This 

 is by no means the case. Very frequently, if not always, the 

 character tliat has been once crossed has been affected l)y its 

 opy)osite with which it was mated and whose place it lias taken 

 in the liybrid. It may be extracted therefrom to use in a new 

 combination, but it will be found to be altered. This we hav(' 

 seen to be true for almost every characteristic sufficiently sludiod 

 — for the comb form, the nostril form, cerebral hernia, crest, 

 muff, tail length, vulture hock, foot feathering, foot color, ear 

 lobe, and both general and special plumage color. Everywhere 

 unit characters arc changed ])y hyl)ridizing. 



"How does this fact 'bear i.u the ri\al theorii- of evolution? 



It has an imporiant lu 

 the statements ,>f <lr\ 

 of organisms arc built 

 from another,' and 'T 

 as between the moleci 



1 Besides the Mendelum results s(>e also dc Vries (: 03, 2, p. 396 et seq.) on 

 the crossing of mutants with the parent species. 



