162 EVOLUTION 



operation of natural selection. The theory 

 works well as an interpretation, but what 

 we need is actual proof of discriminate 

 selection, actual evidence that survivors 

 do survive in virtue of particular qualities. 

 A few examples of this in present-day ex- 

 perience will give strength to the belief that 

 similar processes occurred, as Darwin sug- 

 gested, throughout the past. 



It is interesting to note that so strong 

 a selectionist as Weismann considers that 

 natural selection can be proved only in- 

 directly. He says: *'A direct estimation of 

 the relative protective value of the two 

 colours [of a Sphingid caterpillar] is alto- 

 gether out of the question. The survival 

 of the fittest cannot be proved in nature, 

 simply because we are not in a position to 

 decide a priori what the fittest is." As Mr. 

 E. S. Russell remarks: "This is a significant 

 admission from the protagonist of pure 

 Darwinism, but he admits too much. It is 

 true we cannot decide a priori what the fittest 

 is, but we can discover by observation and 

 experiment whether or no protective colour- 

 ation has selective value. A case in point 

 is given by Mr. A. P. di Cesnola in a short 

 but highly interesting paper in *Biometrika' 

 for 1904. 



"It is well known that the 'praying 



