VARIATION AND HEREDITY 123 



ness because it is correlated with another 

 variation of greater momentum or vital value. 



Another result of modern studies on varia- 

 tion requires to be stated very cautiously. 

 Evidence is accumulating to show that 

 organic structure may pass with seeming 

 abruptness from one position of equilibrium 

 to another. Changes of considerable amount 

 sometimes occur at a single leap. These 

 brusque changes are called *' discontinuous 

 variations," or sometimes "sports," and, in 

 certain cases, "mutations." There is nothing 

 new in the suggestion that evolution may 

 sometimes have been by leaps and bounds, 

 for this was a favourite idea of Cuvier's 

 evolutionist contemporary and antagonist, 

 Etienne Geoff roy Saint-Hilaire; and it was 

 also a pet heresy of Huxley's. There is 

 nothing new in recognizing that discontinu- 

 ous variations do occur, for they correspond 

 to Darwin's "single variations" or "sports." 

 What is new is that we are beginning to 

 accumulate facts in regard to their fre- 

 quency and their heritability. 



Sir Francis Galton compared organic 

 structure to a polygonal model, so shaped as 

 to stand on any one of its sides. "The model 

 and the organic structure have the cardinal 

 fact in common, that if either is disturbed 

 without transgressing the range of its sta- 



