416 ii. r. osbokn recti gradations and allometrons 



Geographic Distribution 



Wbetlier the causes of these changes are to be sought in heredity or 

 ontogeny or environment or selection, or in the interactions of these four 

 coefficients of evolution, is a problem which remains obscure to the pale- 

 ontologist working in paleontology alone; but it may be illuminated by 

 the combined observations of the paleontologist and the zoologist in co- 

 operation, a5 proposed in this paper. The zoologist has already demon- 

 strated that there is direct relation between certain types of coloration 

 and environment, -as veil as between certain habitats and harmonic in- 

 crease or decrease in size; it remains to be determined, chiefly by the 

 zoologist, whether certain environments induce uniformly similar allom- 

 etrons. Our present evidence indicates that this is not the case. Anthro- 

 pologists have failed, for example, to establish any definite relation be- 

 tween environment and human head form. Again, the selection-value of 

 allometrons, or changes of proportion, is obvious in certain cases, but not 

 at all apparent in others. Gerritt S. Miller also fails to observe any 

 direct relation between environment and head proportion, although an 

 indirect relation may arise in connection with differences of food and 

 feeding habits in different environments. 



The author h^s already (May, 1914) been promised the cooperation of 

 a number of eminent niammalogists in a comparison of zoologic- with 

 paleontologic data wliich may be fruitful of important results. 



2 Gerritt S. MiUer (May. 1914) observes that there are abundant iUustrations of the 

 direct action of environment on color in mammals, but that as to proportions, size, and 

 cranial characters the case is quite different. In other words, there are plenty of in- 

 stances of color changes of different character affecting many different members of a 

 fauna in the same way. as when we pass from a wet to a dry climate or from a low to 

 a high altitude, but there do not appear to be any parallel set of changes in proportions, 

 size, or structure. 



