tSpz.] Elliot, Tnhcrttance of Acquired Characters. 87 



another subspecies. It seems to me this deduction from the evi- 

 dence is reasonable and more probable than to suppose that the 

 germ of these various forms had a predisposition in some ancestor 

 to produce them. We cannot actually pi'ove that environment 

 has caused these changes, with any more certainty, perhaps, than 

 the theory of germ predisposition can be proved, but this we do 

 know, that desert tracts contain light-colored species, and forests 

 and districts with great rainfall have dark-colored species, and it 

 is a fair assumption that these great differences are caused by en- 

 vironment ; and granting this, have we not an explanation of causes 

 of variation, in some degree at least? 



Additional evidence of the presumed effects of environment in 

 another genus of birds could be produced from Mr. Dwight's ex- 

 haustive paper on Otocoris or Shore Larks, with which you are 

 all familiar, but my time is too brief to consider this portion of 

 my subject any further. If natural selection were all sufficient to 

 produce variations in any particular species, it is reasonable to 

 suppose that it would effect such changes in others under the 

 same environment. But our evidence seems to point the other 

 way, and tliat environment causes variations, and natural selection 

 only assists in their transmission. 



The effect of climatic influence is shown in the changes exhib- 

 ited by the blue butterfly, Lyccejia agrestis.* This occurs in three 

 forms. A and B alternate in Germany as winter and summer 

 forms ; B and C are the winter and summer forms in Italy. The 

 form B occurs In both climates, but appears in Germany as the 

 summer, in Italy as the winter, form. The German winter form 

 A, however, is completely wanting in Italy, while the Italian 

 summer form (var. allojis) does not occur in Germany. 



Duration of life, among individuals, we also regard as a prom- 

 inent factor in the development of species, and cause of variation ; 

 and the longest-lived creatures evolve new forms or variations 

 the slowest. This would seem to be almost paradoxical, for it 

 would appear that the longer an animal was exposed to the influ- 

 ences of its environment the more its immediate oflspring would 

 be impressed by and illustrate those influences. This might be 

 so if reproduction and development were equally rapid in all 

 creatures. But of course tliis is not so. The longest-lived 

 creatures produce the fewest young, and naturally maturity is 



*Eimer, Organic Evolution, p. 126. 



