1 74 Animal Life and Intelligence. 



eye of a flat-fish from one side of the head to the other on 

 the supposition that individual efforts were inherited, until, 

 by an hereditary summation of effort, the eye at last came 

 round. The question is Are we justified in accepting the 

 easier explanation if it he based on a mere assumption, at 

 present unproved, the modus opcrandi of which is in- 

 explicable ? 



Let us consider very briefly these two points first, the 

 "mere assumption;" secondly, "the inexplicable modus 

 opcrandi" Is there any reason why we should not assume 

 the inheritance of effects of use or disuse as a working 

 hypothesis, if it is not in opposition to any known biological 

 law, and if it does enable us to explain certain observed 

 phenomena? I see no such reason. We do not know 

 enough about the causes of variation to be rigidly bound 

 by the law of parcimony. I am not aware of any biological 

 law that would render the acceptance of this view as a 

 provisional hypothesis unjustifiable. 



But how, it is asked, can we accept it if its modus 

 vperandi is inexplicable ? I question the validity of this 

 argument. I fear our knowledge of organic nature is not 

 at present so full and exact as to justify us in excluding 

 an hypothesis because we are not able to give an adequate 

 answer to the question How are these effects produced ? 

 Of course, if it can be shown that no modus operandi is 

 possible, there is an end of the matter. But who shall 

 dare thus to limit the possibilities of organic nature ? 

 And, if possible, then that natural selection in which the 

 neo-Darwinians place their sole trust would certainly 

 develop so advantageous a mode of influence. It is clear 

 that a species sensitive to every shock of the environment 

 on the organism would be unstable, and hence at a dis- 

 advantage. But, on the other hand, the ability to answer 

 by adaptation to long-continued and persistent environ- 

 mental influence or to oft-repeated and consistent per- 

 formance of function would be so distinct an advantage to 

 the species which possessed it, that, if it lay within the 

 possibilities of organic nature, natural selection, always, as 



