DIFFICULTIES AND IMPORTANCE OF THE 

 BIOLOGICAL SPECIES CONCEPT 



ERNST MAYR: museum of comparative zoology. 



HARVARD COLLEGE, CAMBRIDGE, MASSACHUSETTS 



To bring into focus the picture that emerges from this sym- 

 posium one must consider very diverse material on which the 

 seven contributors have based their discussions — living organ- 

 isms and fossils, animals and plants, freshwater and terrestrial 

 organisms, vertebrates and invertebrates.* It would not have been 

 surprising if the seven speakers had represented seven entirely 

 different viewpoints. This did not happen. Indeed, the general 

 agreement among the speakers was quite far-reaching; for in- 

 stance, all speakers with one exception have emphatically 

 endorsed the biological species concept. Yet it is evident that 

 we have not yet reached a true synthesis. The approach of 

 every worker in this field is still largely colored by his intimate 

 knowledge of the material with which he himself works. Let me 

 illustrate this with a few examples. When an ornithologist speaks 

 of "species" he has a phenomenon in mind in which hybridiza- 

 tion or lack of sexuality are of no consequence. He has great 

 difficulty in determining whether or not species in birds and 

 species in plants are the same kind of phenomenon. Or let us take 

 another case. The population geneticist who has emerged in the 

 last thirty years from the typological thinking of mutationism 

 is likely to consider everything as new that he himself is learning 

 about species. He is unaware of the fact that thinking in terms 

 of populations, and indeed the whole biological species concept, 

 came from systematics into genetics rather than the reverse 

 (Mayr, 1955). Population genetics has, often quite independ- 



° The revised version of T. M. Sonneborn s contribution was not avail- 

 able when this discussion was prepared. 



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