vr INSTINCT OF THE CUCKOO 257 



through being enabled to migrate earlier, or through any 

 other cause; or if the young were made more vigorous by 

 advantage being taken of the mistaken instinct of another 

 species than when reared by their own mother, encum- 

 bered as she could hardly fail to be by having eggs and 

 young of different ages at the same time ; then the old 

 birds or the fostered young would gain an advantage. 

 And analogy would lead us to believe that the young thus 

 reared would be apt to follow by inheritance the occasional 

 and aberrant habit of their mother, and in their turn 

 would be apt to lay their eggs in other birds' nests, and 

 thus be more successful in rearing their young. By a 

 continued process of this nature I believe that the strange 

 instinct of our cuckoo has been developed. It has also 

 recently been ascertained on sufficient evidence, by Adolf 

 Muller, that the cuckoo occasionally lays her eggs on the 

 bare ground, sits on them, and feeds her young. This rare 

 event is probably a case of reversion to the long lost 

 aboriginal instinct of nidification." 



Thus here again is conspicuous the importance ascribed to 

 chance, on which Darwin bases his whole theory; and for this 

 very reason I devote particular consideration to the instinct 

 of the cuckoo. It seems to me a, priori impossible that 

 instincts can be explained by mere accidents, and it seems to 

 me especially impossible that the young bird derived from 

 an egg which was accidentally laid in the nest of another 

 species should " by inheritance " be more likely " to follow 

 the occasional and aberrant habit of its mother" of the 

 mother which it had never seen. If there is any greater 

 inclination in the young bird, it can only be, in my opinion , 

 the inclination acquired from the experience wh'ich it passed 

 through in the nest of its foster-parents during its own 

 youth ; 1 through the impressions it received of its foster- 



1 Cf. Walter, Brehm's Thierleben, second edition, vol. iv. p. 217. 

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