354 DARWINIANA. 



part or phase of that something which directs and de- 

 termines the expenditure of force, then it is not subject 

 to the laws of the latter, and there is no ground for 

 inferring its exhaustibility. The limited vitality is an 

 unproved and unprovable conjecture. The evolutive 

 force, dying out in the using, is either the same con- 

 jecture repeated, or a misapplied analogy. 



After all — apart from speculative analogies — the 

 only evidences we possess which indicate a tendency 

 in species to die out, are those to which Mr. Darwin 

 has called attention. These are, first, the observed 

 deterioration which results, at least in animals, from 

 continued breeding in and in, which may possibly be 

 resolvable into cumulative heritable disease ; and, 

 secondly, as already stated (p. 346), what may be 

 termed the sedulous and elaborate pains everywhere 

 taken in Nature to prevent close breeding — arrange- 

 ments which are particularly prominent in plants, the 

 greater number of which bear hermaphrodite blossoms. 

 The importance of this may be inferred from the uni- 

 versality, variety, and practical perfection of the ar- 

 rangements which secure the end ; and the inference- 

 may fairly be drawn that this is the physiological im- 

 port of sexes. 



It follows from this that there is a tendency, seem- 

 ingly inherent, in species as in individuals, to die out ; 

 but that this tendency is counteracted or checked by 

 sexual wider breeding, which is, on the whole, amply 

 secured in Nature, and which in some way or other 

 reenforces vitality to such an extent as to warrant 

 Darwin's inference that " some unknown great good 

 is derived from the union of individuals which have 



