Changes in Populations | 129 



phenotype becomes .25/. 53 = .47. Hence, s is equal to .53, coinci- 

 dentally the same value as the percent recovery of the melanics. It 

 is highlv unlikely that these results were due to chance alone 

 (P < .01). Similar experiments in unpolluted areas have given 

 reverse results. The relationship between the release-recapture ex- 

 periments and the observations of visual predation is this: The re- 

 lease-recapture work shows that selection occurs; the observations 

 show what the selective agents are. 



Fig. 7.3 I Distribution of Biston hetularia, showing proportion of 

 typicals and melanics. {From Kettlewell, 1958, Heredity 12.) 



m*^-: 



^J}/'-^*^ 



^^'l^,.-^-Nfl^ 



O Typical 

 A Melanic 



