32 2 COOK 



variation, but a condenser is not to be reckoned as a source of 

 light. 



The kinetic theory therefore definitely abandons selection as 

 a cause or positive factor, and perceives that the influence of 

 selection, powerful though it be in many cases, is of a negative 

 and restrictive character — an influence which could not be 

 exerted if the species were not already in motion. 



The kinetic theory, though departing radically from the 

 doctrine of selection as an evolutionary cause, is, in a practical 

 sense, much nearer to Darwinism than are many other sug- 

 gestions which, though intended to supplement the selection 

 hypothesis, would in reality completely nullify it, by denying to 

 selection any true power to influence the course of evolutionary 

 progress. The kinetic theory, though denying that selection is 

 in any proper sense an evolutionary cause, ascribes to it a 

 definite evolutionary function. The environment does not carry 

 the species into adaptive specialization, it only deflects the 

 normal specific motion. The evolution is in the species, the 

 power of deflection in the environment. 



Professor De Vries clearly recognizes that the function of 

 selection is regulative and not active, though he still refers to it 

 as a cause of evolution. 



" Notwithstanding all these apparently unsurmountable diffi- 

 culties, Darwin discovered the great principle which rules the 

 evolution of organisms. It is the principle of natural selection. 

 It is the sifting out of all organisms of minor worth through the 

 struggle for life. It is only a sieve, and not a force of nature, 

 no direct cause of improvement, as many of Darwin's adver- 

 saries, and unfortunately many of his followers also, have so 

 often asserted. It is only a sieve, which decides which is to 

 live, and what is to die. But evolutionary lines are of great 

 length, and the evolution of a flower, or of an insectivorous 

 plant is a way with many sidepaths. It is the sieve that keeps 

 evolution on the main line, killing all, or nearly all that try to 

 go in other directions. By this means natural selection is the 

 one directing cause of the broad lines of evolution. " 



" Of course, with the single steps of evolution it has nothing to 

 do. Only after the step has been taken, the sieve acts, elimi- 



