xiii INSTINCT AND REASON 337 



tether will allow him to go. Hut within his narrow 

 limits he still continues to gain by experience. It is 

 generally said that one bird builds a nest just as 

 another of the same species does, hence intelligence 

 cannot come into play at all. It is probable, though, 

 that there are differences which escape our notice ; at 

 an)- rate, as I have shown, individuals are capable of 

 adapting themselves to new circumstances, and some 

 authorities hold that a bird's first nest is decidedly 

 inferior to her later ones. 



We conclude, then, that nest building is instinctive 

 but that intelligence to some extent works up- 

 on and modifies the instinct. It is no argument 

 against this that birds in captivity often build a very 

 poor nest or are incapable of building one at all. 

 Among domesticated animals instincts are apt to go 

 wrong. There is a breed of hens that never sit upon 

 their eggs. Among the lowest class in our big towns 

 unnatural conditions of life not unfrequently lead to 

 the decay of an instinct on which the continuance of 

 the race depends, the affection of mother for child, an 

 instinct which is never deficient in savage races. 



The Cuckoo Instinct. 



The habits of the Cuckoo are so marvellous that if 

 we were to come fresh to the subject, we should be lost 

 in astonishment at them. But, as Lucretius says, 

 even the sun ceases in time to be an object of wonder. 

 The Cuckoo lays many eggs, and we can hardly be 

 wrong in seeing a connection between this fact and 

 the parasitic habit. They are laid, some ornithologists 



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