FIFTEENTH LECTURE. 



THE AIMS OF THE QUANTITATIVE STUDY OF 



VARIATION. 



C. B. DAVENPORT. 



THERE are two fields of investigation possessed of well- 

 defined methods whose rise and development have character- 

 ized the advance of zoological morphology in the present 

 decade. The first of these is experimental morphology, or (to 

 use a more restricted term) experimental embryology. Experi- 

 mentation is not new, even in morphology, but there has been 

 a decided advance upon the methods in vogue a century ago. 

 The second new field of investigation is the precise, quantita- 

 tive study of variation. The method is here also in part old, 

 having long been used in anthropology ; but in its application 

 to zoology in the strict sense it is quite new. I wish to point 

 out what are the aims of this study. 



The aim of quantitative variation study may be stated gener- 

 ally to be the investigation of the specific 1 form, including the 

 laws of its development and maintenance in the individual, the 

 laws of intermingling of specific forms in the progeny of 

 parents having dissimilar specific forms ; and the laws of evo- 

 lution of new specific forms in nature; i.e., the method of 

 origin of species. I will treat of these three subdivisions of 

 the field of quantitative investigation in inverse order. 



In studying specific differentiation in nature we shall find it, 

 first of all, necessary to investigate species as we find them in 



1 " Specific " is here used in a broad sense to cover the form-peculiarities of 

 families, communities, races, species, genera, in short, peculiarities constant to a 

 group of related individuals of whatever extent. 



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