HETEROGONY AND EVOLUTION 



TABLE XIII 



221 



Relative skull- 

 height, per cent 



272-6-277-5 



267-6-272-5 



262-6-267-5 



257-6-262-5 



252-6-257-5 



460-1 465-1 47 " 1 475" 1 480-1 



-465 -470 -475 -480 -485 



Absolute skull-size (1. + br. + h.), mm. 



A Mean of the three main racial stocks of Britain, early Mediterranean 



(Neolithic), Alpine (Beaker), and Nordic (Anglo-Saxons). 



B Fourteenth and fifteenth century villagers, Northants. 



C London plague skulls, seventeenth century, probably poor stock. 



D Eighteenth century, London, poor neighbourhood. 



E Soldiers, eighteenth century. 



F Twentieth century, poor classes. 



G Twentieth century, educated and well-to-do classes. 



ample of change of relative proportions with change of absolute 

 size. 



As suggested by Hooton (1931, p. 408), a similar effect may- 

 be responsible for the changes in skull-form of the descendents 

 of immigrants into the U.S.A., made familiar by the work 

 of Boas. 



All the cases we have so far considered have another aspect 

 of interest. They are all examples of what Darwin called 

 correlated variation, where change in one character auto- 

 matically brings about change in another character (unless 

 counter-selection operates against the correlated change). 

 Thus they relieve us of the necessity for seeking utilitarian 

 explanations for the correlated changes ; natural selection 

 need not be invoked to account for the details of such char- 

 acters. 



The burden on natural selection is also appreciably light- 



