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 will 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 jaws 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. Recurring 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 beloAv the best working standard, and 
preserving only those that are fully up to it; and, remembering 
further, 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 
