NATURAL SELECTION, ETC. 119 



in one grand system," equally conspire to suggest tliat 

 the connection is one similar or analogons to gen- 

 eration. Surely no naturalist can be blamed for 

 entering somewhat confidently upon a field of specula- 

 tive inquiry wliicli here opens so invitingly ; nor need 

 former premature endeavors and failures utterly 

 dishearten him. 



All these things, it may naturally be said, go to 

 explain the order, not the mode, of the incoming of 

 species. But they all do tend to bring out the gen- 

 eralization expressed by Mr. Wallace in the formula 

 that "every species has come into existence coincident 

 both in time and space with preexisting closely-allied 

 species." ISTot, however, that this is proved even of 

 existing species as a matter of general fact. It is ob- 

 viously impossible to prove anything of the kind. But 

 we must concede that the known facts strongly suggest 

 such an inference. And — since species are only con- 

 geries of individuals, since every individual came into 

 existence in consequence of preexisting individuals of 

 the same sort, so leading up to the individuals with 

 which the species began, and since the only material 

 sequence we know of among plants and animals is that 

 from parent to progeny — the presumption becomes 

 exceedingly strong that the connection of the incoming 

 with the preexisting species is a genealogical one. 



Here, however, all depends upon the probability 

 that Mr. Wallace's inference is really true. Certainly 

 it is not yet generally accepted ; but a strong current 

 is setting toward its acceptance. 



So long as universal cataclysms were in vogue, and 

 all life upon the earth was thought to have been 



