4 CONCEPTS AND DEFINITIONS 



mals he was impressed by the fluidity of the species border and 

 the subjectivity of their delimitation. The views of both Linnaeus 

 and Darwin underwent a change during the life of each. With 

 Linnaeus the statements on the constancy of species became less 

 and less dogmatic through the years. In Darwin, as the idea of 

 evolution became firmly fixed in his mind, so grew his conviction 

 that this should make it impossible to delimit species. He finally 

 regarded species as something purely arbitrary and subjective. "I 

 look at the term species as one arbitrarily given for the sake of 

 convenience to a set of individuals closely resembling each other, 

 and that it does not essentially differ from the term variety which 

 is given to less distinct and more fluctuating forms. . . . The 

 amount of difference is one very important criterion in settling 

 whether two forms should be ranked as species or variety." And 

 finally he came to the conclusion that "In determining whether 

 a form should be ranked as a species or a variety, the opinion of 

 naturalists having sound judgment and wide experience seems 

 the only guide to follow" (Darwin, 1859). Having thus elimi- 

 nated the species as a concrete unit of nature, Darwin had also 

 neatly eliminated the problem of the multiplication of species. 

 This explains why he made no effort in his classical work to 

 solve the problem of speciation. 



The seventy-five years following the publication of the Origin 

 of Species (1859) saw biologists rather clearly divided into two 

 camps, which we might call, in a somewhat oversimplified man- 

 ner, the followers of Darwin and those of Linnaeus. The followers 

 of Darwin, which included the plant breeders, geneticists, and 

 other experimental biologists minimized the "reality" or objectiv- 

 ity of species and considered individuals to be the essential units 

 of evolution. Characteristic for this frame of mind is a symposium 

 held in the early Mcndelian days, which endorsed unanimously 

 the supremacy of the individual and the nonexistence of species. 

 Statements made at this symposium (Bcssey, 1908) include the 

 following: "Nature produces individuals and nothing more. . . . 

 Species have no actual existence in nature. They are mental con- 

 cepts and nothing more. . . . Species have been invented in order 

 that we may refer to great numbers of individuals collectively." 



