SHORTER ARTICLES AND DISCUSSION 



VARIATION, CORRELATION AND INHERITANCE OF 

 FERTILITY IN THE MAMMALS 

 The purpose of this review is to give an outline of the prob- 

 lems of fertility in the mammals (exclusive of man) which may- 

 be solved by the application of biometric formula? to statistical 

 data, to furnish an index to the available statistics, and to indi- 

 cate the results to which the statistical analyses of the raw ob- 

 servations have led. Many of the biometric constants are pub- 

 lished here for the first time. 



Type and Variation ix Fertility 

 The most fundamental biological questions which can be asked 



ently of any other charact, ristic of tin onjn „isn) . its ancestry or 

 its environment are three : 



(a) What is the typical and average fertility of different spe- 

 cies or races? 



(&) What is the variation, within the race, in reproductive 

 activity as compared with that of variation in the degree of 

 development of somatic characters? 



(c) May fertility, like the bodily attributes of organisms, be 

 described by mathematical curves? 



With more comprehensive data concerning other character- 

 istics of the individual organism, its ancestry or environment, 

 more varied problems may be investigated, but none of more 

 fundamental importance. 



With respect to (a) it need only be said initially that biolog- 

 ically a knowledge of the number of offspring characteristic of 

 a species has the same importance as a knowledge of any other 

 of its peculiarities. That species may differ widely in fertility 

 as in other characteristics is obvious without the collection of 

 extensive statistics or the application of mathematical formulae. 

 It is only in a consideration of relatively slight differences in 

 fertility in nearly related species or races or in individuals of 

 the same race existing under various conditions, that biometric 

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