E. MAYR 5 



Taxonomists, one of the speakers claimed, did not merely name 

 the species found in nature but actually "made" them. "In 

 making a species the guiding principle must be that it shall be 

 recognizable from its diagnosis." A leftover from this period is 

 the statement of a recent author: "Distinct species must be sep- 

 arable on the basis of ordinary preserved material." 



It is a curious paradox in the history of biology that the redis- 

 covery of the Mendelian laws resulted in an even more unrealistic 

 species concept among the experimentalists than had existed 

 previously. They either let species saltate merrily from one to 

 another, as did Bateson and DeVries, defining species merely 

 as morphologically different individuals, or they denied the ex- 

 istence of species altogether except as inter/grading populations. 

 Whether these early Mendelians considered species as continuous 

 or discontinuous units, they all agreed in their arbitrariness and 

 artificiality. There is an astonishing absence of any effort in this 

 school to study species in nature, to study natural populations. 



A study of natural populations had become the prevailing pre- 

 occupation in an entirely independent conceptual stream,- that 

 of the naturalists, which ultimately traces back to Linnaeus. The 

 viewpoint of the naturalist was particularly well expressed by 

 Jordan (1905), who stated "The units of which the fauna of a 

 region is composed are separated from each other by gaps which, 

 at a given place, are not bridged by anything. This is a fact 

 which can be checked by any observer. Indeed, the activity of 

 a local naturalist begins with the searching out of these units 

 which with Linnaeus we call species." (For a more detailed 

 discussion see Mayr, 1955. ) Although this was the prevailing 

 viewpoint among taxonomists, it was completely ignored by the 

 general biologists by whom, as a result of Darwin's theory, "Spe- 

 cies were mostly regarded merely as arbitrary divisions of the 

 continuous and ever changing series of individuals found in na- 

 ture ... of course, active taxonomists did not overlook the 

 existence of sharply and distinctly delimited species in nature — 

 but as the existence of those distinct units disagreed with the 

 prevailing theories, it was mentioned as little as possible" (Du 

 Rietz, 1930). The two streams of thought are still recognizable 



