PSYCHOLOGICAL AND ETHICAL ASPECTS. 275 



evils as in human society, while the crimes of sexuality are also 

 lessened by the limitations of definite breeding seasons. With- 

 out exposing the details of the crime list, it will be instructive, 

 as a concrete illustration, to discuss at some length the parasitic 

 instinct of the cuckoo. 



Every schoolboy knows that the female cuckoo shirks the 

 brooding sacrifice usually associated with bird maternity. 

 But though as the Scriptures say, somewhat too severely, 

 of the ostrich, "she is hardened against her young ones, as 

 though they were not hers," she is not "deprived of wisdom ;" 

 by an elaborate and well-executed trick she foists her several 

 eggs, at intervals of a few days, into the nests of various birds, 

 which are usually insectivorous and suited for the upbringing 

 of the intruder. The foster-parents, all unconscious of being 

 fooled, hatch the cuckoo egg among their own. The nestling 

 grows rapidly, and is a dog in the manger by birth. Greedy 

 and jealous, he (the pronoun is oftenest correct) soon asserts 

 his monopoly of nest and food and care, by the summary evic- 

 tion of the rightful tenants, whether they be still passive in ovo 

 or more awkwardly assertive as nestlings. The result is the 

 success of the stronger. 



Of this habit there are various explanations, but the pre- 

 valent one regards it as only a special case of a universal 

 method which favours selfishness. Jenner was the first to 

 emphasise what he regarded as obvious advantages of the 

 trick. The bird has but a short time to stay in its breeding 

 area, and much to do in that short time. "Nature," he said, 

 " has a call upon it to produce a numerous progeny," and as it 

 is at the same time advantageous to migrate early, the gain of 

 leaving the eggs to a succession of other birds to incubate is 

 manifest. Darwin supposed the habit to crop u|) as a mere 

 fortuitous variation, as it occasionally does in the normally 

 nesting American cuckoo. The result was an advantage to 

 the parent, and also to the offspring ; the former got away 

 sooner, the latter were better cared for. Those that learned 

 the trick prospered, those that did not were eliminated ; and so, 

 in virtue of its natural or unnatural success, the device passed 

 from being exceptional to become universal, became in fact an 

 inherited specific instinct. Commenting upon this, Romanes, 

 in a surely somewhat sanguine passage, says : " We have here 

 a sufficiently probable explanation of the raison d^etre of this 

 curious instinct ; and whether it is the true reason, or the only 



