278 THE EVOLUTION OF SEX. 



growth, the nesthng expresses the constitution of the species in 

 its selfish monopohsing greed and insatiable appetite. Obser- 

 vations are recorded of the persistence of the cruel disposition 

 into adolescence, though it usually wanes with the anatomical 

 peculiarity of the back, not very long after birth. The young 

 form at any rate exhibits the essential character of the species. 



(8.) Some corroboration is obtanied from the character of 

 the American cuckoo. There seems no doubt that it is occa- 

 sionally parasitic, and it is interesting to note that observers 

 speak of its unnaturally careless indifference for the fate of its 

 young. The character in fact is less markedly evil ; the occa- 

 sional parasitism is just as intelligible as the occasional "rever- 

 sion " of our cuckoo to ancestral habits, even in some cases to 

 apparent affection for the young. 



(9.) In the cow-birds, again, where the habit occurs in 

 different species in different degrees of perfection (if the term 

 be admissible), the character is strikingly immoral. In one 

 species {Afolotln-us cadius), a nest may be simply stolen, or the 

 rightful nestlings may be thrown out, or actual parasitism may 

 occur as an exception. In M. caiiarieiisis, the eggs may be 

 dropped on the bare ground, or fifteen to twenty from different 

 parents may be lazily and of course fatally huddled together in 

 one nest. Two cuckoo eggs are sometimes found in one nest. 

 In M. pecoris^ which is polygamous, the crime has been 

 evolved, and the habit is that of our cuckoo, one eg^ being 

 laid in each foster-nest. The important point is the general 

 immorality and reproductive carelessness, which in one species 

 finds expression in an organised device. 



Conclusion. — The general character of the birds — the un- 

 social life, the selfish cruelty of the nestlings, and the lazy para- 

 sitic 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 of males, the 

 absence of true pairing, the degeneration of maternal affection, 

 are all correlated, and largely explicable, in terms of the funda- 

 mental contrast between nutrition and reproduction, between 

 hunger and love. Similar unnatural or immoral instincts in 

 o-ther birds, in mammals, and even in the lower animals, are 

 explicable in similar terms. The cuckoo's habit is a natural 

 outcrop of the general character or constitution, only one 

 expression of a dominant diathesis. 



