A COUNTER CRITICISM. 155 



been produced ? Only by decreased function — by the habitual 

 use of soft food, joined, possibly, with the disuse of the teeth as 

 tools. And now mark that this cause operates upon all members 

 of a society which falls into civilised habits. Generation after 

 generation this decreased function changes its component fami- 

 lies simultaneously. Natural selection does not cover the case 

 at all — has nothing to do with it. And the like happens in 

 multitudinous other cases. Every species spreading into a 

 new habitat, coming in contact with new food, exposed to a 

 different temperature, to a drier or moister air, to a more irregu- 

 lar surface, to a new soil, &c., has its members one and all sub- 

 ject to various changed actions, which influence its muscular, 

 vascular, respiratory, digestive, and other systems of organs. 

 If there is inlieritance of functionally-produced modifications, 

 then all its members will transmit the structural alterations 

 wrought in them, and the species will change as a whole without 

 the supplanting of some stocks by others. Doubtless in respect 

 of certain changes natural selection will co-operate. If the 

 species, being a predaceous one, is brought, by migration, into 

 the presence of prey of greater speed than before ; then, while 

 all its members will have their limbs strengthened by extra 

 action, those in whom this muscular adaptation is greatest will 

 have their multiplication furthered; and inheritance of the 

 functionally-increased structures will be aided, in successive 

 generations, by survival of the fittest. But it cannot be so with 

 the multitudinous minor changes entailed by the modified life. 

 The majority of these must be of such relative unimportance 

 that one of them cannot give to the individual in which it be- 

 comes most marked, advantages which predominate over kindred 

 advantages gained by other individuals from other changes 

 more favorably wrought in them. In respect to these, the in- 

 herited effects of use and disuse must accumulate independently 

 of natural selection. 



To make clear the relations of these two factors to one an- 

 other and to heredity, let us take a case in which the operations 

 of all three may be severally identified and distinguished. 



Here is one of those persons, occasionally met with, who has 

 an additional finger on each hand, and who, we will suppose, is a 

 blacksmith. He is neither aided nor much hindered by these 

 additional fingers; but, by constant use, he has greatly devel- 

 oped the muscles of his arm. To avoid a perturbing factor, we 

 will assume that his wife, too, exercises her arms to an unusual 

 degree : keeps a mangle, and has all the custom of the neighbor- 

 hood. Such being the circumstances, let us ask what are the 

 established facts, and what are the beliefs and disbeliefs of 

 biologists. 



