12 CERTAIN EVIDENCE OF 



species, the transition of a species into one or more 

 new varieties," is the answer. Now, so far as these 

 facts can be proved "by experiment, they actually 

 have long since been experimentally proved in the 

 completest manner. For what are the numberless 

 trials of artificial selection for breeding purposes 

 which men have practised for thousand of years in 

 breeding domestic animals and cultivated plants, but 

 physiological experiments which prove the transforma- 

 tion of species ? As an example we may refer to the 

 different races of horses and pigeons. The swift race- 

 horse and the heavy pack-horse, the graceful carriage- 

 horse and the sturdy cart-horse, the huge dray-horse 

 and the dwarfed pony these and many other " races " 

 are so different from each other, that if we had found 

 them wild we should certainly have described them as 

 quite different varieties of one species, or even repre- 

 ^entatives of different species. Undoubtedly, these 

 so-called " races " and " sports " of the horse tribe dif- 

 fer from each other in a much greater degree than 

 do the zebra, the quagga, the mountain horse, arid the 

 other wild varieties of the horse, which every zoologist 

 distinguishes as " bonse species." And yet all these 

 artificial varieties, which man has designedly produced 

 by selection, are descended from a single common 

 parent-form, from one wild " true variety." The same 

 is the case with the numerous and highly differing 



