LOCAL AND SPECIFIC VARIETIES OF INSTINCT. 251 



inhabiting a certain restricted area exhibits a marked depar-jj 

 ture from the instincts elsewhere characteristic of its genus, ' 

 we can scarcely question that the departure is indeed a 

 departit7'e — i.e., that originally the instincts were the same 

 as those occurring in the rest of the genus, but that owing to 

 peculiar local conditions, local variations of instinct arose 

 and were continued till they became hereditary, and so led 

 to a parting aiuay of the instincts of this species from those 

 of its allies.* 



For the sake of brevity I shall here confine my instances 

 to those which may be drawn from Birds. 



The following concise statement of facts relating to the 

 strong instinct of parasitism in the only two genera of birds 

 where it is known to occur, is quoted from an Editorial note 

 in "Land and Water" (Sep. 7, 1867), and displays very 

 remarkable and instructive cross-relations as regards the 

 existence and absence of this instinct in the sundry species 

 composing these tw^o genera. 



" The only non-cuculine genus of birds knowm up to the 

 present time, which has the habit of entrusting its egg to the 

 charge of strangers, is that of the cow-buntings (Molothrus), 

 and the parasitic habit of M. pecoris of North America has 

 been amply described by the ornithologists cited by our 

 correspondent. There are several other species of this genus, 

 and the same parasitic habit was observed in another of them 

 by Mr. Darwin. The Molothri are birds belonging to the 

 great American family of Cassicidce,. which corresponds to 

 that of Sturnidce in the Old World; and they are nearly 

 akin to the troopials {Agelaius). It is remarkable that not 

 any of the various American Cuadidce are parasitic ; w^hereas 

 several genera of this family inhabiting the major continent 

 and its islands, with Australia, are now well known to be so. 



* From the above remarks it will appear that I do not agree with 

 Mr. Darwin in his view, expressed in the Appendix, that cases of specific 

 variation of instinct are difficulties in the way of his theory of the gradual 

 development or evolution of instincts. On the contrary, for the reasons 

 given above, I regard such cases as corroborations of this theory. The 

 source of tliis difference of opinion is, that while Mr. Darwin is above all 

 things anxious to find evidence of connecting links in the formation of an 

 instinct, I feel that to expect such evidence in every ease of instinct would 

 be unreasonable, if not inconsistent with the theory that innumerable in- 

 stincts owe their present existence to the destruction througli natural selec- 

 tion of the animals wliich presented them in a lesser degree of perfection. I 

 shall recur to this point in a future chapter. 



