186 FROM THE GREEKS TO DARWIN 



first clearly pointed out the two criteria of a spe- 

 cies as permanence of form and of appearance 

 and non-fertility with other species; and by a 

 number of dry, descriptive writers, who worked 

 upon the larger groups of animals and plants. 



But the actual turning-point to modern sys- 

 tematic zoology and botany, following the His- 

 toria Animalium of Aristotle, was the great work 

 of Linnseus, the Systema Naturce, the first edi- 

 tion of which appeared in 1735. This was a work 

 of transcendent genius, for throughout the ani- 

 mal and plant world Linnaeus clearly preceived 

 and described the fundamental relationships and 

 differences between genera and species which 

 were ultimately destined to be grouped afresh 

 into the great branching tree of life as distin- 

 guished from the scale of life of all previous 

 writers. The binary system of nomenclature 

 therein proposed was a mere medium for the ex- 

 pression of his broad conceptions of the relation 

 of animals and plants to each other — for exam- 

 ple, Homo sapiens, giving the genus and species 

 together. 'Species' were in his mind — at least in 

 this early period of his thought — the units of di- 

 rect creation ; each species bore the impression of 

 the thought of the Creator, not only in its exter- 

 nal form but in its anatomical structure, its fac- 

 ulties, its functions; and the final purpose of 

 classification was to consider all these facts and 



