THE LAWS OF VARIABILITY. 71 



tion, 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 conditions of life continually inducing fresh varia- 

 bility. We have seen that when the seeds of pears, plums, 

 apples, etc., are sown, the seedlings generally inherit some 

 degree of family likeness. Mingled with these seedlings, 

 a few, and sometimes many, worthless, wild-looking plants 

 commonly appear, and their appearance may be attributed 

 to the principle of reversion. But scarcely a single seed- 

 ling will be found perfectly to resemble the parent-form ; 

 and this may be accounted for by constantly recurring 

 variability induced by the conditions of life. 



STEPS BY WHICH DOMESTIC EACE8 HAVE BEES" PRODUCED. 



Ori<nn of Some effect may be attributed to the direct 



Species, and definite action of the external conditions 

 page of life, and some to habit ; but he would be a 



bold man who would account by such agencies for the 

 differences between a dray and race horse, a greyhound 

 and blood-hound, a carrier and tumbler pigeon. One of 

 the most remarkable features in our domesticated races is 

 that we see in them adaptation, not, indeed, to the ani- 

 mal's or plant's own good, but to man's use or fancy. 

 Some variations useful to him have probably arisen sud- 

 denly, or by one step ; many botanists, for instance, be- 

 lieve that the fuller's teasel, with its hooks, which can not 

 be rivaled by any mechanical contrivance, is only a variety 

 of the wild Dipsacus ; and this amount of change may 

 have suddenly arisen in a seedling. So it has probably 

 been with the turnspit-dog ; and this is known to have 

 been the case with the ancon sheep. But when we compare 

 the dray-horse and race-horse, the dromedary and camel, 



