THE DIRECT ACTION OF THE ENVIRONMENT 97 



deteriorated when placed in the shade, as do European dogs in India 

 and horses in the Falklands. But in all these cases the change, 

 when clearly germinal, when it is transmitted and so increases from 

 generation to generation, is ever a deterioration, not an adaptation. 

 The germ-plasm in those cells that develop into offspring is altered 

 and injured, but not sufficiently to cause its death or even to 

 prevent the development of the individual. Now, obviously, the 

 deterioration cannot continue, generation after generation, in- 

 definitely. If not checked, the race must perish eventually. 

 But there are plants that dwell in the shade, there are native 

 races of dogs in India, and some varieties of horses flourish in 

 climates severer than that of the Falklands, and so on. They 

 are said to have become ' acclimatized,' to have reached an 

 'equilibrium' meaningless terms unless it be explained what 

 they imply. They really imply adaptation, an essential feature 

 of which consists in the germ-plasm becoming insusceptible to the 

 direct action of the environment. Thus if, amongst Clayton's 

 beans, there had been any germs the plasm of which had so varied 

 as to be unaffected by shade, then, since he obtained seed in the 

 first three generations, he could have established by Natural 

 Selection a race as capable of existing away from the influence of 

 direct sunshine as mosses and ferns. He failed because, instead 

 of proceeding step by step, he made the conditions too rigorous. 

 When captive, wild animals are sterile, though still displaying 

 sexual desires ; it is possible, in some cases at least, that the 

 germ-plasm in their germ-cells is so altered as to be incapable of 

 directing development. 



157. We observed that medical men are in the habit of 

 declaring that parental diseases and intemperance usually result 

 in filial degeneration, and we noted that this inference could not 

 possibly be correct, for otherwise the human race would have long 

 ago become extinct ; whereas, on the contrary, it has everywhere 

 undergone protective evolution. It is possible, nay probable, that 

 disease and intemperance are sometimes, though rarely i.e. under 

 exceptional conditions or in exceptional germ-cells causes of 

 variations ; but, in view of their long-continued prevalence, which 

 has made them quite as * normal ' a part of the environment as the 

 dangers to which other types of animals and plants are exposed, 

 in view also of the fact that in every case protective racial evolution, 

 not deterioration, has occurred, it is hard to understand how 

 they can be constant or even frequent causes of the variations 

 which are seen in children and adults. Nevertheless, suppose we 



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