216 I The Process of Evolution 



variation in 12 characters is summarized in Table 10.1. No overall 

 pattern of variation is evident; indeed, many of the characters seem 

 to vary completely independently. Moore's detailed studies of vari- 

 ation in developmental processes have yielded abundant provoca- 

 tive data. For instance, northern and southern populations of R. 

 pipiens show different temperature-tolerance ranges for normal 

 embryological development (Fig. 10.2). These differences parallel 

 those found between northern and southern frogs belonging to 

 clearly distinct clusters. (For example, the northern R. sylvatica, 

 which ranges from the subarctic to the central United States, can 

 develop normally between 2.5 and 24°C, whereas R. catesbiana, 



After Moore, Bull. Am. Mus. Nat. Hist., 82, 1944. 



