78 The Higher Usefulness of Science 



by studying a given species of plant or animal he could 

 tell when it is going to give rise to a mutation and just 

 what the mutant would be? It is highly probable that 

 after a large amount of critical knowledge of muta- 

 tions occurring in particular groups has been accumu- 

 lated, something in the way of rules or laws of muta- 

 tion will be made out, and that it will be possible to 

 say in a general way that such and such mutations 

 may be expected. But no one should fail to see what 

 a vastly different matter this would be from fore- 

 telling by examining a given plant or animal as such, 

 that it will produce a predescribed mutant at a speci- 

 fied time. 



The cases of natural genesis, inorganic and organic, 

 which we have considered, show two things of great 

 importance for our general conception of nature: 

 first, that there is a limit beyond which scientific pre- 

 diction of generative processes can not go, either in 

 inorganic or in organic nature; but second, that this 

 limit is so placed that it leaves no need for the assump- 

 tion of extra- or supernatural forces to account for 

 what is produced. 



These limitations to prediction are due, as we have 

 seen, mainly to the fact that observational knowledge 

 is excluded from direct hold upon what is latent in 

 nature. But at the same time that the very nature of 

 our knowledge limits our ability to predict future 

 natural products, it gives us certainty that the gen- 

 erators are the sufficient explanation of the products. 



