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PREFACE 



Few biological problems have remained as consistently chal- 

 lenging through the past two centuries as the species problem. 

 Time after time attempts were made to cut the Gordian knot and 

 declare the species problem solved either by asserting dogmat- 

 ically that species did not exist or by defining, equally dogmat- 

 ically, the precise characteristics of species. Alas, these pseudo- 

 solutions were obviously unsatisfactory. One might ask: "Why 

 not simply ignore the species problem?" This also has been tried, 

 but the consequences were confusion and chaos. The species is a 

 biological phenomenon that cannot be ignored. Whatever else the 

 species might be, there is no question that it is one of the primary 

 levels of integration in many branches of biology, as in syste- 

 matics (including that of microorganisms), genetics, and ecology, 

 but also in physiology and in the study of behavior. Every living 

 organism is a member of a species, and the attributes of these 

 organisms can often best be interpreted in terms of this relation- 

 ship. This is particularly true in comparative studies. 



The continued interest in the species problem thus requires no 

 apology. Indeed the interest in the species is perhaps greater now 

 than it has been at any other time during the last hundred years. 

 One reason for this is the increase in autecological investigations, 

 which include a joint study of the physiological and ecological 

 properties of species that has resulted in an active contact be- 

 tween physiology and ecology, with the species the area of over- 

 lapping interest. A second reason is the current tendency in popu- 

 lation genetics to study the interaction, rather than the action, of 

 genes, and thus to lead to a study of gene pools of which the 

 species is the largest. A third is the emergence of a rejuvenated 

 new systematics that devotes much of its attention to the intimate 

 study of the population structure of species, a new school that is 

 strongly represented in the southeastern United States. It is not 

 surprising therefore that the species problem received more votes 

 than any other subject when Dr. J. G. Carlson, Chairman of Sec- 



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