A Three-fold Development. 149 



as a fact that no two individuals of the same species are 

 ever exactly alike. There is in each a continual tendency 

 to vary. We so frequently hear it said that no two per- 

 sons are just alike. No two leaves can be found in which 

 a difference cannot be detected. Is it possible for us to 

 learn what causes this difference in two organisms of the 

 same species growing side by side, and apparently sur- 

 rounded by the same conditions? But first, is the en- 

 vironment ever just the same for any two individuals of 

 the same species, or has it been for the ancestors of those 

 individuals? We have already seen from what has been 

 said before that the inorganic world has been, from its 

 very beginning, subject to continual change, from phys- 

 ical and astronomical causes. Before it had cooled suf- 

 ficiently so that its climate could have depended at all 

 on the heat derived from the sun, there must have been 

 a constant change going on in its cooling crust. There 

 would have been a constant breaking up of the slowly 

 cooling exterior, caused by the pouring deluges of hot 

 water, thick with mineral and acid solutions, which 

 would act with terrific force in breaking and disintegrat- 

 ing the slowly cooling rocks. That combat of the ele- 

 ments began with the beginning of time on our earth 

 and has continued to the present, although with always 

 diminishing force. Now, having the facts of this cease- 

 less change in the inorganic world and the constant ten- 

 dency to variability of the organic life which peoples it, 

 how are these two series of facts connected? The com- 

 mon observation of all people teach them certain facts 

 concerning plants and animals. Here in the north we 

 can raise great crops of apples and cherries, but when 

 we go to Flor-ida we look in vain for an apple or cherry 

 tree, while e find orange and guava trees all about us. 

 There the pineapple grows as readily in the open air as 

 the cabbage does here. There the Palma Christi or cas- 

 tor oil bean grows from year to year into a large tree, 

 while here it is a small shrub, killed by each year's frost. 

 There the mocking bird makes its home all through the 

 year, while here the little English sparrow is as common. 

 The swarming life of those southern oceans is almost en- 

 tirely different from that of our northern seas. We say. 



