VARIATION AND MENDELIAN INHERITANCE 375 



case, about 0.3.^ This means, as ordinarily interpreted, that in 

 each local race part of the variability is hereditary and part non- 

 hereditary, this last component being regarded as 'somatic' in 

 origin. 



One essential feature of these geographic races remains, how- 

 ever, to be examined somewhat further. It has been shown that 

 the shifting of mode by which one 'race' arose historically from 

 another must have involved the simultaneous shifting of a con- 

 siderable number of different modes. And this occurred even 

 among characters which, in their every-day inheritance, do not 

 seem to be linked together to any appreciable extent. More- 

 over, characters (e.g., foot and pelvis), which appear to be cor- 

 related positively in the individual, appear in some cases to have 

 been modified in opposite directions in the course of phylogeny. 



I have pointed out in earlier papers that in respect to both 

 coat color and the width of the dorsal tail stripe a general cli- 

 matic sequence is discernible among these races, and this con- 

 clusion appears to be borne out, on the whole, by the additional 

 data presented below. I have also called attention to the agree- 

 ment between my own findings in this regard and those of vari- 

 ous mamriialogists and ornithologists, who have recognized the 

 existence of an increase in pigmentation pari passu with an in- 

 crease in the atmospheric humidity of their habitat. If we con- 

 sider only the coastal stations from San Francisco Bay north- 

 ward (Berkeley, Duncan Mills, Fort Bragg, Eureka), which 

 probably present a graded series in respect to both temperature 

 and atmospheric humidity, we find likewise a similar gradation in 

 respect to the mean width of the tail stripe and the mean length 

 of the tail, foot, and ear. The suggestion lies close at hand that 

 we have to do with some more or less direct influence of environ- 

 ment, which, in the course of time, has modified the hereditary 

 characters of the animals dwelling at these various points.^ 

 Perhaps the four characters just named have undergone simul- 

 taneous modification by some single external agency, and this 



* American Naturalist, June- July, 1918, p. 294. 



' This supposition might, of course, be expressed in such terms as would ex- 

 clude the 'inheritance of acquired characters.' 



