EVOLUTION NOT THE ORIGIN OF SPECIES. 455 



ticated instances of distinctly prepotent variations are known, and such 

 were taken by Mivart and other zoologists to prove that species do not 

 originate by gradual change, but abruptly or by ' extraordinary births, ' 

 a view quite similar to the recently published 'Theory of Mutations,' 

 but distinctly more practical because the 'mutations' of plants which 

 are the basis of the inferences of Professor De Yries are not prepotent 

 but 'recessive,' presumably because they do not represent true genetic 

 variations, but are symptoms of what may be described as an evolution- 

 ary debility, due to inbreeding. The disappearance of mutative char- 

 acters when the new variations are crossed with the parent form or 

 with each other is merely the recovery, as it were, of the health of the 

 species when the abnormal condition of inbreeding has been removed, 

 as shown so conclusively in Darwin's well-known experiments with 

 pigeons, and confirmed by an abundance of similar facts. 



Though differently interpreted, many other facts supporting this 

 view were collected by Darwin, who summarized the results of his 

 studies of I'pomea, Digitalis, Origanum, Viola, Bartonia, Canna and 

 the common cabbage and pea, as follows: 



"The most important conclusion at which I have arrived is that the 

 mere act of crossing by itself does no good. The good depends on the 

 individuals which are crossed differing slightly in constitution, owing 

 to their progenitors having been subjected during several generations 

 to slightly different conditions, or to what we call in our ignorance 

 spontaneous variations."* 



Differences between the plants of different habitats mean also dif- 

 ferent lines of descent and attendant variations, and the beneficial re- 

 sults of bringing these together may be explained by reference to sym- 

 basis rather than to the ' slightly different conditions. ' 



While it may not be insisted that species, as described and named 

 by systematists, are never originated by 'extraordinary births,' or from 

 'mutations,' both suppositions are obviously improbable as general ex- 

 planations. Mutations are seldom fitted to survive because they are 

 less vigorous and less fertile than the parent type, so that they must 

 be segregated at once in order to be preserved. And even prepotent 

 variations have no necessary connection with the origination of species, 

 since however rapidly the characters of a species might change, it would 

 still be the same species until a subdivision had taken place. The more 

 a species evolves the more different from its relatives it becomes, and 

 the more satisfactory for the purposes of systematic study, but this 

 progressive transformation of the 'type' carries with it no necessity for 

 subdivision, nor any indication that evolution is concerned with the 

 origination of species. 



* Darwin, ' The Effects of Cross and Self Fertilization in the Vegetable 

 Kingdom,' p. 27. New York, 1895. 



