Chap. XII. 



INHERITANCE. 



25 



that it is overborne by hostile or unfavourable conditions of life. 

 No one would expect that our improved pigs, if forced during 

 several generations to travel about and root in the ground for 

 their own subsistence, would transmit, as truly as they now do, 

 their tendency to fatten, and their short muzzles and legs. Dray- 

 horses assuredly would not long transmit their great size and 

 massive limbs, if compelled to live on a cold, damp mountainous 

 region; we have indeed evidence of such deterioration in the 

 horses which have run wild on the Falkland Islands. European 

 dogs in India often fail to transmit their true character. Our 

 sheep in tropical countries lose their wool in a few generations. 

 There seems also to be a close relation between certain peculiar 

 pastures and the inheritance of an enlarged tail in fat-tailed sheep, 

 which form one of the most ancient breeds in the world. With 

 plants, we have seen that the American varieties of maize lose 

 their proper character in the course of two or three generations, 

 when cultivated in Europe. Our cabbages, which here come so 

 true by seed, cannot form heads in hot countries. Under changed 

 circumstances, periodical habits of life soon fail to be transmitted, 

 as the period of maturity in summer and winter wheat, barley, 

 and vetches. So it is with animals; for instance, a person 

 whose statement I can trust, procured eggs of Aylesbury ducks 

 from that town, where they are kept in houses and are reared 

 as early as possible for the London market ; the ducks bred from 

 these eggs in a distant part of England, hatched their first brood 

 on January 24th, whilst common ducks, kept in the same yard 

 and treated in the same manner, did not hatch till the end of 

 March; and this shows that the period of hatching was inherited. 

 But the grandchildren of these Aylesbury ducks completely 

 lost their early habit of incubation, and hatched their eggs at 

 the same time with the common ducks of the same place. 



Many cases of non-inheritance apparently result from the con- 

 ditions of life continually inducing fresh variability. We have 

 seen that when the seeds of pears, plums, apples, &c, are sown, 

 the seedlings generally inherit some degree of family likeness 

 from the parent-variety. Mingled with these seedlings, a few, 

 and sometimes many, worthless, wild-looking plants commonly 

 appear; and their appearance may be attributed to the prin- 

 ciple of reversion. But scarcely a single seedling will be found 



