344 



ACTION OF NATURAL SELECTION 



For instance, the accompanying figure shows the distri- 

 bution of the weight values of the birds. The curves 

 are very irregular, but it is obvious that the dotted line 

 curve is shifted distinctly to the right, indicating that 

 the eliminated birds were, on an average, heavier. This 

 conclusion has already been obtained by the simple 

 process of taking averages; but the curves show in ad- 

 dition that it is the very heavy birds which were more 



I 15 



4) 



s 



09 



"3 

 310 



^O 







3 



a 



8 



22 23 



24 



30 



31 



32 



25 26 27 28 29 



Weight of birds in grams 



FIG. 28. Distribution of the weights of surviving and of 



eliminated sparrows. 



especially eliminated. Thus of the 14 birds of 27.3 

 gms. and upwards obtained, only three survived. 

 Similarly also in respect of the femur measurements, 

 it was found that of the 19 birds obtained with a femur 

 length of .685 inch or less, only 7 survived whilst 12 

 were eliminated. 



The next generation of birds collected in tEe storm- 

 swept area would accordingly be shorter in length, 

 weigh less, have longer legs, have a longer sternum and 

 a greater brain capacity than the former generation; 

 supposing, of course, that the variations existing in 



