10 THE STUDY OF ADAPTATION. [ixtrod. 



taken by itself, is clearly incapable of interpreting the phenomena 

 of development. We are endeavouring by means of a mass of 

 conflicting evidence to reconstruct the series of Descent, but of the 

 laws which govern such a series we are ignorant. In the inter- 

 pretation of Embryological evidence it is constantly necessary to 

 make certain hypotheses as to the course of Variation in the 

 past, but before this can be done it is surely necessary that w r e 

 should have some knowledge of the modes of Variation in the 

 present. When we shall know something of the nature of the 

 variations which are now occurring in animals and the steps by 

 which they are now progressing before our eyes, w 7 e shall be in 

 a position to surmise what their past has been ; for we shall then 

 know what changes are possible to them and what are not. In 

 the absence of such knowledge, any person is at liberty to pos- 

 tulate the occurrence of variations on any lines which may suggest 

 themselves to him, a liberty which has of late been freely used. 

 Embryology has provided us with a magnificent body of facts, 

 but the interpretation of the facts is still to seek. 



The other method which, since Darwin's work, has attracted 

 most attention is the study of the mechanisms by which organisms 

 are adapted to the conditions in which they live. This study of 

 Adaptation and of the utility of structures exercises an extra- 

 ordinarv fascination over the minds of some and it is most 

 important that its proper use and scope should be understood. 



We have seen that the Embryological Method owed its import- 

 ance to its value as a mode of testing the truth of the Theory 

 of Evolution: in the same way the Study of Adaptation was 

 undertaken as a test of the Theory of Natural Selection. 



Amongst many classes of animals, complex structures are pre- 

 sent which do not seem to contribute directly to the well-being of 

 their possessors. By many it has been felt that the persistent 

 occurrence of organs of this class is a difficulty, on the hypothesis 

 that there is a tendency for useful structures to be retained and 

 for useless parts to be lost. In consequence it has been antici- 

 pated that sufficient research would reveal the manner in which 

 these parts are directly useful. The amount of evidence collected 

 with this object is now enormous, and most astonishing ingenuity 

 has been evoked in the interpretation of it. A discussion of the 

 truth of the conclusions thus put forward is of course apart from 

 our present purpose, which is to examine the logical value of this 

 method of research as a means of attacking the problem of Evo- 

 lution. W T ith regard to the results it has attained it must suffice 

 to notice the fact that while the functions of many problematical 

 organs have been conjectured, in some cases perhaps rightly, there 

 remain w r hole groups of common phenomena of this kind, which 

 are still almost untouched even by speculation, and structures and 

 instincts are found in the best known forms, as to the " utility " of 



