II.] ON HEREDITY, 9 1 



mission of acquired short-sightedness, but to the greater varia- 

 bihty of the eye, which necessarily results from the cessation 

 of the controUing influence of natural selection. 



This suspension of the preserving influence of natural se- 

 lection may be termed Panmixia, for all individuals can re- 

 produce themselves and thus stamp their characters upon 

 the species, and not only those which are in all respects, or 

 in respect to some single organ, the fittest. In my opinion, 

 the greater number of those variations which are usually 

 attributed to the direct influence of external conditions of 

 life, are to be ascribed to panmixia. For example, the great 

 variability of most domesticated animals essentially depends 

 upon this principle. 



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 

 that a rigid selection of individuals with well-developed wings 

 at once ceases among its descendants. Hence in the course 

 of generations, a deterioration of the organs of flight must 

 necessarily ensue, and the other members and organs of the 

 bird will be similarly affected. 



This example very clearly indicates that the degeneration of 

 an organ does not depend upon its disuse ; for although our 

 domestic poultry very rarely make use of their wings, the 

 muscles of flight have not disappeared, and, at any rate in 

 the goose, do not seem to have undergone any marked de- 

 generation. 



The numerous and exact observations conducted by Darwin 

 upon the weight and measurement of the bones in domestic 

 fowls, seem to me to possess a significance beyond that which 

 he attributed to them. 



If the weight of the wing-bones of the domestic duck bears 

 a smaller proportion to the weight of the leg-bones than in 

 the wild duck, and if, as Darwin rightly assumes, this depends 

 not only upon the diminution of the wings, but also upon the 

 increase of the legs, it by no means follows that this latter 

 increase in organs which are now more frequently used, is 

 dependent upon hereditary influences alone. 



It is quite possible that it depends, on the one hand, upon 

 the suspension of natural selection, or panmixia (and these 



