THE 



AMERICAN NATURALIST 



Vol. XLVIII June, 19U No. 570 



SPECIES-BUILDING BY HYBKIDIZATION AND 

 MUTATION 



PROFESSOR JOHN H. GEROULD 

 Dartmouth College 



The mystery that has surrounded the origin of new 

 species in the incipient stages of their evolution has lately 

 been penetrated and cleared away to a large extent by the 

 light of studies in Mendelian inheritance and the attend- 

 ant idea of mutation. Species building is no longer a 

 hypothetical process based on the preservation of minute, 

 useful, fortuitous variations, but it is a process open to 

 observation and experimental control. Its raw materials 

 are variations that are usually not minute, useful or for- 

 tuitous, but clean-cut unit characters, tending to vary 

 only in certain limited, well-defined directions depending 

 upon the chemical peculiarities and physical structure of 

 the particular form of protoplasm, and, in the vast plural- 

 ity of cases, nonuseful. 



The fields of systematic zoology and botany, illumi- 

 nated by the new science, genetics, are emerging from the 

 mists of formalism, and invite biologists of the broadest 

 type to exploration. The geneticist turns to systematics 

 for many of the materials with which to solve the prob- 

 lems of organic evolution. The systematist sees that in 

 order to keep abreast of the times he must stand ready 

 to rebuild his pigeonholes and test with experiment that 

 which he puts into them. 



Every one occupied with zoology or botany realizes 

 that there are no adequate criteria by which this or that 

 assemblage of individuals is or is not to be regarded as a 

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