ORIGIN OF SPECIES. 41 



need hardly be pointed out that the fact does not in the 

 slightest degree interfere with any conclusion that may be 

 arrived at, deductively, from other considerations that, at 

 some time or other, abiogenesis must have taken place. 



If the hypothesis of evolution is true, living matter must 

 have arisen from not-living matter ; for, by the hypothesis, 

 the condition of the globe was at one time such that living 

 matter could not have existed in it, 1 life being entirely in- 

 compatible with the gaseous state. But, living matter once 

 originated, there is no necessity for another origination, since 

 the hypothesis postulates the unlimited, though perhaps not 

 indefinite, modifiability of such matter. 



Of the causes which have led to the origination of living 

 matter, then, it may be said that we know absolutely nothing. 

 But postulating the existence of living matter endowed with 

 that power of hereditary transmission, and with that tendency 

 to vary which is found in all such matter, Mr. Darwin has 

 shown good reasons for believing that the interaction between 

 living matter and surrounding conditions, which results in 

 the survival of the fittest, is sufficient to account for the 

 gradual evolution of plants and animals from their simplest 

 to their most complicated forms, and for the known phe- 

 nomena of Morphology, Physiology, and Distribution. 



Mr. Darwin has further endeavored to give a physical 

 explanation of hereditary transmission by his hypothesis 

 of Pangenesis ; while he seeks for the principal, if not the 

 only cause of variation in the influence of changing condi- 

 tions. 



It is on this point that the chief divergence exists among 

 those who accept the doctrine of evolution in its general 

 outlines. Three views may be taken of the causes of varia- 

 tion : 



a. In virtue of its molecular structure, the organism may 

 tend to vary. This variability may either be indefinke, or 

 may be limited to certain directions by intrinsic conditions. 

 In the former case, the result of the struggle for existence 

 would be the survival of the fittest among an indefinite 

 number of varieties ; in the latter case, it would be the 

 survival of the fittest among a certain set of varieties, the 



1 It makes no difference if we adopt Sir W". Thomson's hypothesis, and 

 suppose that the germs of living things have been transported to our globe 

 from some other, seeing that there is as much reason for supposing that all 

 stellar and planetary components of the universe are or have been gaseous, as 

 that the earth has passed through this stage. 



