6l4 THE HISTORY OF BIOLOGY 



to decide exactly what the categories of the system are intended to denote. 

 Unfortunately it has not been possible to obtain unanimity on this point; 

 opinions have clashed and their advocates have been very little disposed 

 to modify their views. We shall here cite one or two examples of these 

 divergences of opinion. 



Lotsj and the species question 

 The Dutch student of the heredity problem J. P. Lotsy has taken up an 

 uncompromisingly genetical attitude towards the idea of species. "What is 

 a species?" he asks in one of his treatises. The answer is: A species in the 

 Linnasan sense is no species, for it comprises a large number of different life- 

 forms whose outward appearance bears a certain resemblance, but as to 

 whose origin we can determine nothing. The Linnxan species are therefore 

 nothing but products of the imagination, as also the Linn^an genera and 

 other higher classified groups; consequently they should no longer be called 

 species but linn^onts. Nor are the minor species into which some Linnxan 

 species can be divided and which remain constant, true species; these forms, 

 which were specially studied by the French botanist Jordan in the beginning 

 of the nineteenth century, should be named after him jordanonts, but they 

 are not species, for their internal resemblance cannot be ascertained. On the 

 other hand, a species is a summary of all the homozygous individuals having 

 the same hereditary character. "Consequently, not even all the pure-lines in 

 the Johanssenian sense are true species; they are so only if they are at the 

 same time homozygotes. And in regard to organisms with sexless repro- 

 duction, V, e can never know whether they are species, for that can be dis- 

 covered only through the analysis of hybridizing experiments." In these 

 circumstances it becomes a matter for doubt whether any species exist at 

 all in nature. 



This conclusion of Lotsy's clearly proves that an insistence upon the 

 genetical idea of species can only lead to sheer paradox; he admits himself 

 that only linn^eonts and jordanonts can possess any practical systematical 

 significance. The whole of his reasoning is really a striking proof of the 

 power of language over thought; he wants what is called species to be a 

 genetical entity, and so he comes to a point where he does not know whether 

 species in his sense of the word exist at all in nature. Other students of 

 heredity have also taken warning from this result: thus, Heribert-Nilsson 

 declares that the term "species" might well be used in the form in which 

 Linnxus employed it; thereby, it is true, the idea of species becomes purely 

 morphological — "The species of classification is a phylogenetical con- 

 glomerate," he says — but for the genetical entities we have of course 

 the new nomenclature "genotype" and "pure-line." The necessity of 

 thus dispensing with the genetical idea of species has, indeed, been 

 realized by many others; Ernst Lehmann, for instance, maintained in 



