356 THE GRAMMAR OF SCIENCE 



the ground for what is really a metaphysical attack on 

 the Darwinian theory of evolution. As I interpret that 

 theory it is truly scientific, for the very reason that it 

 does not attempt to explain anything. It takes the facts 

 of life as we perceive them, and attempts to describe them 

 in a brief formula involving such conceptions as *' variation," 

 " inheritance," " natural selection," and " sexual selection." 

 But no more than the law of gravitation explains our 

 routine of perceptions with regard to the sun, does Darwin's 

 theory of the origin of species explain our perceptions of 

 change in living forms. Perhaps some of the modern 

 critics of Darwin will be less ready to consider adaptations 

 as " not explicable " by natural selection, but due to the 

 " precise chemical nature of protoplasmic metabolism," or 

 to " an internal fate, expressible in terms of dominant 

 chemical constitution," if they once grasp that physics and 

 chemistry in their turn render nothing " explicable," but 

 merely, like natural selection itself, are shorthand de- 

 scriptions of changes in our sense-impressions. 



^ 12. — Natural Selection in the Inorganic Wo'ld 



There is a problem, however, with regard to natural 

 selection which deserves special attention from both 

 physicist and biologist, namely : Within what limits is 

 the Darwinian formula a valid description ? Assuming 

 the spontaneous generation of life as a plausible, if yet 

 unproven, hypothesis, where are we to consider that selection 

 as a result of the struggle for existence began ? Again, 

 for what, if any, forms of life are we to consider it as 

 ceasing to be an essential factor in descriptive history ? 

 We may not be able to answer these questions definitely, 

 but some few words at least must be said with regard to 

 their purport. 



In the first place we notice that as soon as we conceive 

 a perfectly gradual and continuous change from inorganic 

 to organic substance, then we must either call upon the 

 physicist to admit that natural selection applies to inorganic 

 substances, or else we must seek from the biologist a 



