CHAPTER XVI. 



THE LAWS OF VAIilATION. 



I 



IN" the last chapter we have seen that the habitual Changes 

 characters of organisms are subject to two quite dis- fui^ction- 

 tinct classes of changes, which, following Herbert Spencer, ally pio- 

 I shall call functioncdly produced changes and S2?ontaneoiLS g,-^^^.' 

 variations. I shall have to speak, farther on, of a kind of taneous. 

 changes concerning which it is difficult to say how they 

 are to be classed. I have to some extent, though in ex- 

 treme outline, traced in the last chapter the laws according 

 to which changes are functionally produced, and I now go 

 on to state the conditions which are favourable to variation. 

 I must, however, begin by stating a set of laws that have 

 no very obvious connexion with the subject. 



We have seen that great and sudden changes of habit 

 are impossible, and that great and sudden changes of 

 external circumstances are destructive to an organism. 

 Whatever may be the connexion of these two laws with 

 each other (and I believe it is very close), their opposites 

 are also true : slight changes of habit are possible, and Benefit of 

 slight changes of external circumstances are beneficial to '^^^&^^ 



o _ ° • changes. 



organisms. Concerning the variability of habit, I need not 

 say anything more at present ; but, as an instance of the 

 beneficial effect of slight changes of external circumstances, 

 may be mentioned the proverbial benefit of " change of air " Change of 

 — that is to say, in reality, change. of external circumstances '''"'■ 

 — in renewing the bodily and mental health, especially 

 of sufferers from monotonous, depressing, or exhausting oc- 

 cupation ; and the equally well-known benefit of " changing Change of 

 the seed " of cultivated plants — that is to say, bringing the ^'^'^ ' 



