SPECIES CONCEPTS AND DEFINITIONS 



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ERNST MAYR: museum of comparative zoolog% 



HARVARD COLLEGE, CAMBRIDGE, MASSACHUSETTS 



The importance of one fact of nature is being recognized to an 

 ever increasing extent: that the living world is comprised of more 

 or less distinct entities which we call species. Why are species so 

 important? Not just because they exist in huge numbers, and be- 

 cause each species, when properly studied, turns out to be differ- 

 ent from every other, morphologically and in many other respects. 

 Species are important because they represent an important level 

 of integration in living nature. This recognition is fundamental to 

 pure biology, no less than to all subdivisions of applied biology. 

 An inventory of the species of animals and plants of the world 

 is the base line of further research in biology. Whether he realizes 

 it or not, every biologist — even he who works on the molecular 

 level — works with species or parts of species and his findings may 

 be influenced decisively by the choice of a particular species. 

 The communication of his results will depend on the correct iden- 

 tification of the species involved, and thus, on its taxonomy. 



Yet, when I was first approached by the Chairman of the Di- 

 vision of Zoology of the American Association for the Advance- 

 ment of Science to organize a symposium on the species problem 

 I was, to put it mildly, hesitant. Much discussion of this subject 

 in recent years suggested that there was perhaps no need for 

 such a symposium. Ensuing correspondence, however, convinced 

 me otherwise, and certain publications showed clearly that fur- 

 ther thinking on this subject is welcome, if not necessary. The 

 species problem continues to be one of the most disputed sub- 

 jects in biology, in spite of the intense preoccupation with it 

 during the past two hundred years. The recent publications by 

 Spurway, Burma, and Arkell attest this. This symposium can be 



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