E. MAYR 3 



stable. Linnaeus had to show that species were not erratic and 

 ephemeral units before organic evolution as we know it could 

 have any meaning." (Conway Zirkle in litt.) The idea that the 

 seed of one plant could occasionally produce an individual of 

 another species was so widespread that it died only slowly. We 

 all know that it raised its ugly head once more during the past 

 ten years. In spite of Redi's and Spallanzani's experiments spon- 

 taneous generation was still used in 1851 by the philosopher 

 Schopenhauer as an explanation for the origin of higher cate- 

 gories. Linnaeus thus did for the higher organisms what Pasteur 

 did one hundred years later for the lower. 



A second reason why his emphasis was important is that it 

 took the species out of the speculations of the philosophers who 

 approached the species problem in the spirit of metaphysics and 

 stated, for instance, that "only individuals exist. The species of a 

 naturalist is nothing but an illusion" (Robinet, 1768). We shall 

 return later to the point why species are more than merely an 

 aggregate of individuals. 



A third reason why the insistence on the sharp delimitation of 

 species in the writings of Linnaeus is of historical importance is 

 that it strengthened the viewpoint of the local naturalist and 

 established the basis for an observational and experimental study 

 of species in local faunas and floras, of which Darwin took full 

 advantage. 



Linnaeus was too experienced a botanist to be blind to the 

 evidence of evolutionary change. Greene (1912) gathered nu- 

 merous citations from his writings which clearly document Lin- 

 naeus' belief in the common descent of certain species, and 

 Ramsbottom ( 1938 ) and Sirks ( 1952 ) have traced how Linnaeus 

 expressed himself more and more freely on the subject, as his 

 prestige grew. Paradoxically, Linnaeus did more, perhaps, to lay 

 a solid foundation for subsequent evolutionary studies by em- 

 phasizing the constancy and objectivity of species than if he, 

 like Darwin, had emphasized the opposite. 



Darwin looked at the species from a viewpoint almost directly 

 opposite to that of Linnaeus. As a traveler naturalist and par- 

 ticularly because of his studies of domesticated plants and ani- 



