No. 620] 



ADAPTATION 



developed out of simple beginnings through (a) direct 

 responses to environmental stimuli, or (b) the ei¥ects of 

 functioning upon the functioning parts themselves. 



The first of these alternatives has been well-nigh dis- 

 carded by scientist and layman alike, and need not be 

 further considered here. I will point out in passing, 

 however, that certain elements of the ''special creation" 

 hypothesis have recently been put forward in the name 

 of science. Of this more anon. 



The second alternative, that of natural selection, is ad- 

 mitted by most biologists to be one of the factors con- 

 cerned in the production of adaptive mechanisms, though 

 it is doubtful whether any two thinkers would agree as 

 to the importance to be assigned to it. The essence of 

 this hypothesis is the contingency of the individual vari- 

 ations in relation to the need to be satisfied. If the vari- 

 ations are directed, in the sense of tending preponder- 

 atingly toward the satisfaction of this need, then our 

 explanation is shifted to a totally new basis. It is this 

 directive tendency, not natural selection, which is the 

 effective agency in evolution. The consequences which 

 would follow such an assumption will be discussed later. 



The third of our alternative hypotheses has figured his- 

 torically as the chief rival of natural selection, though by 

 many (e. g., by Darwin himself), both principles were 

 accepted. One of the merits of the Lamarckian prin- 

 ciple, in the eyes of som6 of its adherents,^' is its apparent 

 rejection of contingency or chance, a fatal weakness, so 

 they believe, in the natural selection theory. But a little 

 thought will show us that the Lamarckian principle, no 

 less than the Darwinian, is based upon chance, as regards 

 the relation between the need and the means to its ful- 

 filment.-^ 



