Chapter II 



THE FOUR GREAT HISTORICAL 



SPECULATIONS 



Looking' backward over the history of the evolution 

 theory we recognize that during the hundred and 

 odd years that have elapsed since Buff on, there have 

 been four main lines of specuJation concerning evo- 

 lution. We might call them the four great cosmogo- 

 nies or the four modern epics of evolution. 



The Environment 



GEOFFROY ST. HILAIRE 



About the beginning of the last century Geoffroy 

 St. Hilaire, protege, and in some respects a disciple, 

 of Buffon, was interested as to how living species are 

 related to the animals and plants that had preceded 

 them. He was familiar with the kind of change that 

 takes place in the embryo if it is put into new or 

 changed surroundings, and from this knowledge he 

 concluded that as the surface of the earth slowly 

 changed — as the carbon dioxide contents in the air 

 altered — as land appeared, and as marine animals 

 left the water to inhabit it, they or their embryos re- 

 sponded to the new conditions and those that re- 

 sponded favorably gave rise to new creations. As the 

 environment changed the fauna and flora changed — 

 change for change. Here we have a picture of pro- 



