Birds by Land and Sea 



in the back disappears ten to twelve days after 

 birth, whilst the impulse to eject seems to die out 

 earlier. 



The line of argument which suggests that the 

 actions of the parent cuckoo are determined by con- 

 sideration for the future welfare of its young would 

 appear to be wholly unsound, if for no other reason 

 than that any direct interest shown by the cuckoo in 

 its offspring is so rare as to be regarded as pheno- 

 menal. Its habits have true causes in anterior con- 

 ditions, and are not to be explained by substituting 

 for the latter fanciful motives having reference to the 

 future welfare of its own offspring, or of the species 

 generally. For, if this be not so, we must admit 

 that the hundred and nineteen species of European 

 birds upon which the cuckoo has been known to 

 father its young, also have their motives for sacrific- 

 ing their broods in the interest of the intruder ; or 

 that, while they are her unconscious dupes, she only 

 sees all along the line, and adapts her actions to the 

 end she has in view. 



A more rational conclusion is that arrived at by 

 Geddes and Thomson in their work, " The Evolution 

 of Sex," p. 278 : "The general character of the 

 birds the unsocial life, the selfish cruelty of the 

 nestlings, and the lazy parasitic habit have a 

 common basis in the constitution. The insatiable 

 appetite, the small size of the reproductive organs, 

 the smallness of the eggs, the sluggish parturition, the 

 rapid growth of the young, the great preponderance 



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