XIV FUNDAMENTAL PROBLEMS 413 



But, as we shall see presently, there is now much reason 

 to believe that the supposed inheritance of acquired modifica- 

 tions — that is, of the effects of use and disuse, or of the direct 

 influence of the environment — is not a fact ; and if so, the very 

 foundation is taken away from the whole class of objections 

 on which so much stress is now laid. It therefore becomes 

 important to inquire whether the facts adduced by Darwin, 

 Spencer, and others, do really necessitate such inheritance, or 

 whether any other interpretation of them is possible. I 

 believe there is such an interpretation ; and we mil first 

 consider the cases of disuse on which Mr. Spencer lays most 

 stress. 



The cases Mr. Spencer adduces as demonstrating the effects 

 of disuse in diminishing the size and strength of organs are, 

 the diminished size of the jaws in the races of civilised men, 

 and the diminution of the muscles used in closing the jaAvs in 

 the case of pet- dogs fed for generations on soft food. He 

 argues that the minute reduction in any one generation could 

 not possibly have been useful, and, therefore, not the subject 

 of natural selection ; and against the theory of correlation of 

 the diminished jaw with increased brain in man, he urges that 

 there are cases of large brain development, accompanied by 

 jaws above the average size. Against the theory of economy 

 of nutrition in the case of the pet-dogs, he places the abundant 

 food of these animals which would render such economy need- 

 less. 



But neither he nor Mr. Darwin has considered the effects 

 of the withdrawal of the action of natural selection in keep- 

 ing up the parts in question to their full dimensions, which, 

 of itself, seems to me quite adequate to produce the results 

 observed. Kecurring to the evidence, adduced in Chapter III, 

 of the constant variation occurring in all parts of the organism, 

 while selection is constantly acting on these variations in 

 eliminating all that fall below the best Avorking standard, and 

 preserving only those that are fully up to it; and, remembering 

 fui^ther, that, of the whole number of the increase produced 

 annually, only a small percentage of the best adapted can be 

 preserved, we shall see that every useful organ will be kept 

 up nearly to its higher limit of size and efficiency. Now Mr. 

 Galton has proved experimentally that, when any part has 



