212 Variailons and Orthoplasy 



characters which do not actually exist, not does it attempt 

 to say that such or such a thing might exist. On the con- 

 trary, it simply aims to show that such or such an actually 

 existing structure, mode of behaviour, etc., has probably 

 arisen through the operation of the forces and principles 

 which the theory recognizes. The actually existing forms 

 are so varied that different emphasis must be placed, now 

 on one factor of the whole process, now on another. In- 

 stinct, for example, seems to require, for any explanation 

 approaching adequacy, the factor of accommodation to 

 supplement that of natural selection. Mimicry and those 

 anatomical and structural characters in which the element 

 of function is much reduced, seem to be explained by 

 natural selection with little supplementing from other 

 factors. It may be found ultimately that Lamarckian 

 heredity holds for simple organisms and for plants, while 

 in higher organisms and in mammals it is not operative. 

 The problem in each case, therefore, may be stated thus : 

 the fact is that such an organ exists ; its utility can be 

 explained only on the supposition that accommodation 

 cooperated with any congenital variations which may have 

 existed ; it has thus evolved up to the stage which it 

 actually shows — complete function, partial function, mere 

 beginning, as the case may be ; it is quite possible, had 

 the conditions favoured it, that its evolution might have 

 gone farther, or, indeed, not so far ; but that it did go so 

 far, and no farther, is in itself sufficient evidence of the 

 utility of the cooperation of heredity and accommodation 

 in its production.^ 



^ See the insistence on Natural Selection in Professor LI. Morgan's * New 

 Statement,' in Appendix A. 



