306 THE FITNESS OF THE ENVIRONMENT 



evolutionary processes, or there does not. If 

 such an explanation be possible, at least it 

 must be admitted that it is very hard to con- 

 ceive. Yet, recalling the difficulty before the 

 idea of natural selection arose of imagining any 

 mechanistic explanation whatever of fitness, 

 we shall do well not to decide against such a 

 possibility. 



On the other hand, it is conceivable that a 

 tendency could work parallel with mechanism 

 without interfering with it, according to a 

 view which has been held by such thorough- 

 going mechanists as Descartes, Claude Ber- 

 nard, Virchow, DuBois-Reymond, and many 

 another. Although I have no intention of 

 here seeking a choice between these two hy- 

 potheses, being in fact convinced that now, 

 at all events, no choice is scientifically possi- 

 ble, and doubting if properly speaking they are 

 alternatives at all, 1 I do feel concerned to 



1 "Either the multitudinous kinds of organisms which now 

 exist, and the far more multitudinous kinds which have existed 

 during past geologic eras have been from time to time sep- 

 arately made, or they have arisen by insensible steps, through 

 actions such as we see habitually going on. Both hypotheses 

 imply a Cause. The last, certainly as much as the first, 

 recognizes this Cause as inscrutable. The point at issue is, 

 how this inscrutable Cause has worked in the production of 

 living forms. This point, if it is to be decided at all, is to be 

 decided only by examination of evidence. Let us inquire 

 which of these antagonistic hypotheses is most congruous 



