THE CAUSATION OF DISEASE. 229 



are healthy in all respects, are of delicate muscular build. 

 Individuals thus constituted may enjoy good health though 

 they lead a life of comparative muscular inactivity, and this 

 often happens in the case of active brain workers. 



It is possible that perfect adaptation to a muscularly inac- 

 tive mode of life might in the course of time take place — 

 always supposing the individual to lead in every other respect 

 a perfectly healthy life, the change being wrought by a sum- 

 mation of personal adaptations and a survival of the fittest, that 

 is, by both direct and indirect equilibration. An excess of 

 motor activity is not an inevitable concomitant of life, for some 

 animal organisms are actually stationary. It is true that great 

 muscular activity characterizes the vast majority of animals, 

 since in the struggle for food the muscular system is kept in 

 constant use, and, indeed, its very evolution arises out of this 

 struggle ; but there is no reason why, if no longer needed for 

 active work, it should not dwindle to very scanty propor- 

 tions without injury to health, mental vigour, and longevity, 

 the whole organism gradually adapting itself to the new mode 

 of life. Thus there might evolve a mere " walking brain," 

 so to speak. The physiologist may cry out against this argu- 

 ment, urging that a certain measure of muscular activity is a 

 physiological necessity, that without it the various glandular 

 organs — as, for instance, the skin and liver — would fail in 

 their duty, and that such an inactive mode of life must 

 inevitably lead to degeneration and extinction,* I see, how- 

 ever, no reason why the whole of the body should not become 

 adapted to the new order of things, provided the E remained 

 stable from generation to generation. 



But the E not being thus stable from generation to genera- 

 tion, such an adaptation will probably never take place, and 

 it is very unlikely that many successive generations will ever 

 lead a highly inactive mode of life ; moreover, the pro- 

 creative power of man would appear, according to Herbert 

 Spencer, to diminish with the advance of mental evolution. 

 These considerations, however, do not negative the fact that 



* Kingsley, in his " Water Babies," makes the over-developed heads collapse 

 like " watery turnips ! " 



R 



