German mastiff 

 English bloodhound 



Pointer Newfoundland 

 Bulldog Shepherd 



Greyhound Spitz 



FlG. 408. ARTIFICIAL SELECTION. Its effects in causing varieties in one species. 

 Which of the dogs is specialized for speed ? Driving cattle ? Stopping cattle ? 

 Trailing by scent ? Finding game ? Drawing vehicles ? Going into holes ? 

 House pet ? Cold weather ? In Mexico there is a hairless dog specialized for hot 

 climates. The widely differing environments under various forms of domestica- 

 tion cause " sports " which breeders are quick to take advantage of when wishing 

 to develop new varieties. Professor De Vries by cultivating American evening 

 primroses in Europe has shown that a sudden change of environment may cause 

 not only varieties but new species to arise. 



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