IXTRODVCTION. 425 



lands showed so great differences that an ex- 

 perienced eye could tell from which island a 

 given specimen was brought. Darwin goes 

 on : "I never dreamed that islands about fifty 

 or sixty miles apart, and most of them in sight 

 of each other, formed of precisely the same 

 rocks, placed under a quite similar climate, 

 rising to a nearly equal height, would have 

 been differently tenanted.' 1 The physical en- 

 vironment was quite similar in all, but the or- 

 ganic variation seemed to go on. Birds of 

 the same species in the separate islands va- 

 ried, so did the flowers. Here then was vari- 

 ation with the consequent evolution into dis- 

 tinct species, mapped out by localities and set 

 directly under the eye. Insular species of 

 plants, animals and insects fenced off by the 

 sea and confined to limited territory in the 

 separate islands, always show differences in 

 their individuals. Here is the clew to Dar- 

 win's chapter on Variation Under Nature (in 

 Origin of Species}. Seeing this phenomenon 

 oft repeated in a little enclosed spot, Darwin 

 carries it home and applies it to the whole 

 earth; he has found the typical fact of his 

 work, and at once proceeds to make the same 

 universal. But first he is driven to find the 

 source of such variation. 



Darwin fully recognized the foregoing or- 

 ginal suggestion of his idea. Says he in his 



