CHAPTER II. 



SUGGESTIONS FOR RELIABLE HYPOTHESES OF 

 EVOLUTION. 



THE main point which prevented investigators, like 

 Cuvier and his disciples, from accepting a genetic 

 connection between the present and previous animal 

 and plant forms of different appearance, was the con- 

 viction that the organisms always retained their specific 

 peculiarities. It could not be conceived that the earlier 

 living beings had so greatly changed that they could often 

 only be allocated to the same family or even sub-order, 

 in a few cases even to the same genus, but only quite 

 exceptionally to the same species as the present ones. 

 The constancy of the systematic species of the present 

 is, however, not established ; rather are there facts which 

 directly indicate a capacity of variation or can be satis- 

 factorily explained only by acceptance of such. 



1. Direct observation and the facts of animal and 

 plant geography. 



(1) Direct observation and experiment. 



Breeding experiments show, in the first place, that 

 under purposeful supervision of the reproduction very 

 varied forms can arise, which often remain constant as, 

 for instance, dogs, cattle, pigeons, and the remarkable 



