3+8 NATURAL SCIENCE. Mav, 



shelter and nourish the reproductive elements can produce some kind 

 of effect upon them, and though reproductive elements may persis- 

 tently affect other reproductive elements, as in the case of Lord 

 Morton's mare, yet such and similar facts do not in the least decide 

 the question whether the cells, or units, of the bodily structure can 

 affect the reproductive substance, or germ-plasm, in such a way as to 

 convey their particular acquired modifications, or changes, to 

 posterity. 



A few words are also necessary in answer to the claim that since 

 congenital characters are heritable, the onus of proving that acquired 

 characters are " not inheritable " falls upon the Neo-Darwinian. The 

 implication that the one case affects the other cannot be sustained. 

 It is perfectly certain and perfectly well-known that there is a wide 

 difference between the two classes of characters, and that they are 

 not comparable in their degree of effect upon heredity — otherwise 

 there would be no more dispute concerning the one class than con- 

 cerning the other. No one questions the immediate and decisive 

 heritability of congenital mutilations and malformations, or of any other 

 congenital peculiarity, however striking or minute. On the other 

 hand, it is a matter of general experience that the loss of a tooth, or 

 eye, or limb, or finger-joint, is no more transmitted to offspring than 

 a sunburnt complexion, or a clipped beard, or a knowledge of Latin 

 or cookery. In proportion as the nature of each case admits of clear 

 decisive proof, we see that acquired characters are 7iot inherited ; 

 no indisputable evidence to the contrary has ever been given. 

 The presumption arising from the proven facts, therefore, is that non- 

 inheritance of acquired characters is the general rule, and the onus 

 probandi, therefore, rests with those who assert the contrary. We 

 cannot prove a vmiversal negative ; and it is not easy to find or 

 suggest absolutely decisive tests of the admittedly slight power of use- 

 inheritance, or of the size-reducing power of panmixia. The effect of 

 use-inheritance on offspring is imperceptible. Darwin acknowledges 

 that several generations must elapse before any appreciable result 

 follows ;'■> and during this interval other factors would be at work. 

 We perceive the apparently insuperable difficulty, or practical 

 impossibility, of excluding all other factors in such delicate and com- 

 plicated cases. But if the Neo-Lamarckian will accept his own cases, 

 and allow us to adopt his own assumption that extraneous factors are 

 adequately excluded, we can show that the effects of use and disuse 

 are not inherited in some features just as conclusively (or inconclusively) 

 as he shows that, in other respects, they are inherited. If, for instance, 

 use-inheritance is proved by the shortening of the less used wing- 

 bones of the domestic duck, or the leg-bones of the rabbit, then it is 

 disproved by the thickening of these bones ; and, conversely, if it is 

 proved by the marked thinness or lightness of the wing-bones of the 



'•' Variation of Animals and Plants under Domestication, vol. ii,, p. 288. 



