TilE INFLUENCES OF ENVIRONMENT 279 



of climate and food may play in the transmutation of species. We 

 can give no answer from experience, because there is an entire lack 

 of perfectly satisfactor}- and clear experiments ; we only know in 

 a few cases how great the variations are which can be brought about 

 in the body during the individual life by means of any of these 

 factors. In most cases it is uncertain whether actually hereditary 

 effects play any part, that is, whether the germ-plasm itself is aft'ected. 

 But if we wish to be theoretically clear as to how far direct climatic 

 effects may go, we may say this, that they may operate as long as they 

 cause no disturbance in the life of the species concerned, for at the 

 moment that such a direct effect begins to be prejudicial to the species 

 personal selection will step in, and, hy preferring the individuals which 

 react least strongly to the climatic stimulus, will inhibit the variation. 

 If in any case this should be physically impossible, the species would 

 die out in the climate in question. That a species of plant or animal 

 has climatic limits indicates that individuals which go beyond these 

 are exposed to influences which make life impossible and which natural 

 selection is unable to neutralize. We are here brought face ^ to face 

 with one of the limits to the scope of natural selection. Tliere is no 

 doubt that the influences of the environment must always have 

 a powerful eflect upon the soma of the individual, but we have seen, 

 in the case of Alpine plants and of galls, how very far this eflect may 

 go without leaving any trace in the germ-plasm. 



