490 Mr. J. D. Dana on Species. 



Moreover, in both kingdoms, if hybridity be begun, nature 

 commences at once to purify herself as of an ulcer on the sy- 

 stem. It is treated like a disease, and the energies of the species 

 combine to throw it off. The short run of hybridity between 

 the horse and the ass, species very closely related, reaching its 

 end in one single generation, instead of favouring the idea that 

 perpetuated fertile hybridity is possible, is a speaking protest 

 against a principle that would ruin the system if allowed free 

 scope. 



The finiteness of nature in all her proportions, and the neces- 

 sity of finiteness and fixedness for the very existence of a king- 

 dom of life, or of human science, its impress on finite mind, are 

 hence strong arguments for the belief that hybridity cannot 

 seriously trifle with the true units of nature, and, at the best, 

 can only make temporary variations. 



It is fair to make the supposition, that in case of a very close 

 proximity of species, there might be a degree of fertile hybridity 

 allowed ; and that a closer and closer affinity might give a longer 

 and longer range of fertility. But the case just now alluded to 

 seems to cut the hypothesis short ; and moreover it is not reason- 

 able to attribute such indefiniteness to nature's outlines, for it 

 is at variance with the spirit of her system. 



Were such a case demonstrated by well-established facts, it 

 would necessarily be admitted ; and I would add, that investi- 

 gations directed to this point are the most important that modern 

 science can undertake. But until proved by arguments better 

 than those drawn from domesticated animals, we may plead the 

 general principle against the possibilities on the other side. If 

 there is a law to be discovered, it is a wide and comprehensive 

 law, for such are all nature's principles. Nature will teach it, 

 not in one corner of her system only, but more or less in every 

 part. We have therefore a right to ask for well-defined facts, 

 taken from the study of successive generations, of the inter- 

 breeding of species known to be distinct. 



Least of all should we expect that a law, which is so rigid 

 among plants and the lower animals, should have its main ex- 

 ceptions in the highest class of the animal kingdom, and its 

 most extravagant violations in the genus Homo ; for if there be 

 more than one species of Man, they have become in the main 

 indefinite by intermixture. The very crown of the kingdom has 

 been despoiled ; for a kingdom in nature is perfect only as it 

 retains all its original parts in their full symmetry, undefaced 

 and unblurred. Man, by receiving a plastic body, in accordance 

 with a law that species most capable of domestication should 

 necessarily be most pliant, was fitted to take the whole earth as 

 his dominion, and live under every zone. And surely it would 



