BREEDING FROM CLOSE AFFINITIES. 189 



concrete forces, must influence the whole structure. This 

 they do, beyond denial, and sexual distinctions must espe- 

 cially influence, to some extent in early life, to a great extent 

 iu adult life. 



Inbreeding — Crossing. — Close inbreeding has a tendency 

 to induce sterility, while crossing is universally regarded by 

 breeders as brinsrins: vi^or. Darwin regards it as an estab- 

 lished law of nature, that all organic beings profit from an 

 occasional cross with individuals not closely related to them 

 in blood ; and that, on the other hand, long-continued close 

 interbreeding is injurious. It is the belief of physiologists 

 that every act of development 'ends to diminish the germinal 

 capacity, while every act of generation tends to renew it ; and 

 it is even probable that in plants even self-fertilization seldom 

 occurs, but the stigma receives pollen from other flowers than 

 its own through contrivances often of the most wonderful 

 complexity. This is a form of expression for the fact that 

 every change is brought about through the utilization of a 

 force, and that the forces may gradually become weakened in 

 producing changes unless a power of regeneration be given 

 them by a union with fresh forces. In inbreeding we are 

 dealing with forces of a similar character, — that is, they 

 approximate to a nearer likeness than do the forces ^ the 

 product of an out-cross, on account of having a greater 

 similarity of history in their past. We consequently have an 

 approach towards the development of new individuals without 

 the intervening act of generation, — as, by fission, gemma- 

 tion, etc. ; that is, an approach towards a developmental 

 process, as distinguished from the generative process, and, 

 consequently, a tendency to shorter duration to the life, — this 

 means weakness, lessened constitution, etc., etc. In an out- 

 cross, on the other hand, we have an entire departure from the 

 developmental idea towards the generative, and a consequent 

 vigor, or renewal of force. If the out-cross be, however, too 

 violent, a hybrid may be the result, — that is, the forces neces- 

 sary for fertility are absent, either on account of too great 

 antagonism between the forces present in either parent, or 

 because they are not of such a nature as to combine. In 

 hybrids, therefore, we have usually sterility, but also the 

 possibility of producing offspring, — as, indeed, is occasionally 



