TRANSMISSION OF MODIFICATIONS 385 



5. The process may be explained by the old principle of pro 

 gressive variation. 



Of these, the first two are certainly always at work. Mani- 

 festly all the individuals of succeeding generations, or most of 

 them at least, will spontaneously acclimate to the changed con- 

 dition. This of itself would give an appearance of race acclimati- 

 zation, even though no change had been wrought in its inherited 

 nature. If, now, to this is added the effect of selection, we at 

 once recognize a powerful cause of real race acclimatization. 

 Nor does this necessitate the destruction of any very large 

 numbers. If only their life period be shortened or their fer- 

 tility decreased, their relative importance in the race would be 

 greatly lessened thereby and the effect of selection felt. 



Either one of these two processes alone is entirely competent 

 to account for the full appearance of acclimatization. Doubtless 

 both are always present and at work jointly, but this does not 

 preclude the possibility of other agencies also. The fifth possi- 

 bility depends upon selection for its efficiency. 



The chief objection to relying upon selection to fully account 

 for race acclimatization is that the destruction is frequently too 

 slight, and the race response too prompt ; yet it is not sufficiently 

 prompt and instantly complete to account for the phenomena by 

 the successive acclimatization of all individuals separately. 



There is a rapidly cumulative element somewhere. The whole 

 movement is too rapid for selection, especially with the exceed- 

 ingly moderate destruction of individuals that sometimes takes 

 place. Plants do not acclimate by reason of most of them being 

 killed off, yet there is a strongly progressive element involved. 

 The inevitable conclusion is, in the opinion of the writer, that 

 the chief effects of acclimatization are transmitted. 



Whether this transmission be direct or indirect ; whether it 

 be. due to the peculiar development of the individual impressing 

 itself upon the germ, or to climatic influences, like tempera- 

 ture, food, etc., which being all-pervading, affect the general 

 state of life and influence the germ direct, is another and more 

 important matter. 



That the simple removal of a part does not affect transmis- 

 sion is significant. The old contention that the protoplasm of 



