ERASMUS DARWIN. 



145 



Animals, Artificial Selection, and treats Environ- 

 ment almost in its broadest sense. We may briefly 

 follow the outline of his argument for Evolution in 

 the Zoo7iomia. He says : — 



" When we revolve in our minds the metamorphoses of ani- 

 mals, as from the tadpole to the frog ; secondly, the changes 

 produced by artificial cultivation, as in the breeds of horses, dogs, 

 and sheep ; thirdly, the changes produced by conditions of climate 

 and of season, as in the sheep of warm climates being covered 

 with hair instead of wool, and the hares and partridges of northern 

 climates becoming white in winter : when, further, we observe 

 the changes of structure produced by habit, as seen especially in 

 men of different occupations ; or the changes produced by artifi- 

 cial mutilation and prenatal influences, as in the crossing of 

 species and production of monsters ; fourth, when we obser\'e the 

 essential unity of plan in all warm-blooded animals, — we are led to 

 conclude that they have been alike produced from a similar living 

 filament." 



Havinof thus discussed some of the most obvious 

 arguments for mutability, he proceeds to speculate 

 upon the causes of these changes. " Fifthly," he 

 says, " all animals undergo transformations which 

 are in part produced by their own exertions, in re- 

 sponse to pleasures and pains, and many of these 

 acquired forms or propensities are transmitted to 

 their posterity T 



This, so far as I know, is the first clear and 

 definite statement of the theory of the transmission 

 of acquired characters considered as one of the fac- 

 tors of Evolution. We will now continue to ex- 

 amine Darwin's argument, and later will illustrate 



