10 CONCEPTS AND DEFINITIONS 



hundred years in which these questions have been tossed back 

 and forth. This certainly cannot be due to lack of trying, for an 

 immense amount of time and thought has been devoted to the 

 subject during this period. One has a feeling that there is a hid- 

 den reason for so much disagreement. One has the impression 

 that the students of species are like the three blind men who 

 described the elephant respectively as a rope, a column, or a 

 giant snake when touching its tail, its legs, and its trunk. 



Perhaps the disagreement is due to the fact that there is more 

 than one kind of species and that we need a different definition 

 for each of these species. Many attempts have been made during 

 the last hundred years to distinguish these several kinds of 

 species, among the most recent being those of Valentine ( 1949 ) 

 and Cain (1953). Camp and Gillis (1943) recognized no less 

 than twelve different kinds of species. Yet, a given species in 

 nature might fit into several of their categories, and in view of 

 tli is overlap no one has adopted either this elaborate classifica- 

 tion or any of the simpler schemes proposed before or after- 

 wards. 



Species Concepts 



An entirely different approach to the species problem stresses 

 the kaleidoscopic nature of any species and attempts to determine 

 how many different aspects a species has. Depending on the 

 choice of criteria, it leads to a variety of "species concepts" or 

 "species definitions." At one time I listed five species concepts, 

 which I called the practical, morphological, genetic, sterility, 

 and biological (Mayr, 1942). Meglitsch (1954) distinguishes 

 three concepts, the phenotypic, genetic, and phylogenetic, a 

 somewhat more natural arrangement. Two facts emerge from 

 these and other classifications. One is that there is more than 

 one species concept and that it is I utile to search for the species 

 concept. The second is that there are at least two levels of con- 

 cepts. Such terms as "practical," "sterility," "genetic" signify con- 

 crete aspects of species which lead to what one might call "ap- 

 plied species concepts. They specify criteria which can be 

 applied readily to determine the status of discontinuities found 



