Characters, Hereditary and Acquired. 97 



the wild parent stock ; while the reverse was the case 

 with parts less used. Now, although at first sight 

 these facts certainly do seem to yield good evidence 

 of the inherited effects of use and disuse, they are 

 really open to the following very weighty objections. 



First of all, there is no means of knowing how 

 far the observed effects may have been due to in- 

 creased or diminished use during only the individual 

 life-time of each domesticated animal. Again, and 

 this is a more important point, in all Darwin's 

 investigations the increase or decrease of a part 

 was estimated, not by directly comparing, say the 

 wing-bones of a domesticated duck with the wing- 

 bones of a wild duck, but by comparing the ratio 

 between the wing and leg bones of a tame duck 

 with the ratio between the wing and leg bones 

 of a wild duck. Consequently, if there be any reason 

 to doubt the supposition that a really inherited 

 decrease in the size of a part thus estimated is due 

 to the inherited effects of disuse, such a doubt will 

 also extend to the evidence of increased size being 

 due to the inherited effects of use. Now there is the 

 gravest possible doubt lying against the supposition 

 that any really inherited decrease in the size of a 

 part is due to the inherited effects of disuse. For 

 it may be — and, at any rate to some extent, must 

 be — due to another principle, which it is strange that 

 Darwin should have overlooked. This is the prin- 

 ciple which Weismann has called Panmixia, and which 

 cannot be better expressed than in his own words : — 



" A goose or a duck must possess strong powers of flight in the 

 natural state, but such powers are no longer necessary for 

 obtaining food when it is brought into the poultry-yard ; so 



II. H 



