232 COOK 



a sufficient service to have shown that enough variation exists to 

 make evolution feasible or even plausible. The scholastically 

 educated public, which often appreciates arguments much better 

 than facts, was obliged to approach evolution through Darwin's 

 deductions rather than through his perceptions. Evolution was 

 accepted or rejected on the merits of natural selection, though 

 the two ideas have no necessary connection. Natural selection 

 and evolution are both facts, but in proving that the one is the 

 adequate practical cause of the other it would be necessary to 

 show that the variations through which evolution goes forward 

 are caused by natural selection. No such causation has been 

 demonstrated. Natural selection does not furnish the variations 

 nor explain why variations are accumulated and carried for- 

 ward into evolution. It only explains why some variations are 

 preserved instead of others. It does not explain evolution, but 

 shows how the direction of evolution may be influenced by the 

 environment. The causes of evolution, or, to be more explicit, 

 the causes of evolutionary variations, are as mysterious to us as 

 they were to Darwin, and indeed, more so, since the greatest 

 step in evolutionary investigation since the time of Darwin has 

 been a negative one, the destruction of the theory of the inher- 

 itance of characters acquired from the environment. Darwin 

 sometimes placed much importance on variations induced by 

 environment, and invented the theory of pangenesis to explain 

 the inheritance of such, and bring them within the field of nat- 

 ural selection. Without pangenesis and direct inheritance, nat- 

 ural selection loses its place as a positive factor in evolution and 

 becomes purely negative ; it neither causes variations nor 

 causes them to accumulate. The most that can be claimed is 

 that it hastens the development of some characters by retarding 

 others, or by forbidding them entirely. It is apparent in some 

 groups of organisms that the influence of natural selection has 

 been very great, in others that it has been very small, 1 but its 

 effects are in all cases dependent upon the underlying facts, that 

 variations do appear and are accumulated. Natural selection 

 does not explain evolution, except in a very loose and super- 



1 Cook, O. F., 1902. Evolutionary Inferences from the Diplopoda. Proc. 

 Entomological Society of Washington, 5 : 14. 



