INSTINCTS APPARENTLY DETRIMENTAL TO THE SPECIES. 281 



ing that any such modification is urgently required. Now it 

 can scarcely be held probable on these principles that the 

 instinct of crowing on the part of the pheasant should have 

 been modified by natural selection during the short time that 

 his ancestors have been naturalized in this country, and in 

 consequence of one in a hundred having thus fallen a victim 

 to poachers. The case of a wild hen cackling over its eggs 

 may seem a stronger one ; but here again the whole question 

 really consists in the actual percentage of eggs thus discovered 

 by the natives, and I should think this must be exceedingly 

 small. Birds building in exposed situations only become an 

 argument against the modificability of instinct by natural selec- 

 ts hi, when it is shown that the exposure has led to the destruc- 

 tion of nests by man or other animals for a great number of 

 generations ; and this has never been shown. Even in the 

 most remarkable case — that of the Furnarius of La Plata — 

 Mr. Darwin merely says that this bird " in a thickly peopled 

 country, with mischievous boys, ivould soon be exterminated." 

 And similarly it would require to be shown that the habit of 

 the Shrew-mouse at the Mauritius has lonq; led to the 

 destruction of many individuals of each generation by man. 



In all such cases we must remember how very insignifi- 

 cant the influence of man — and especially of savage man — 

 usually is, as compared with the sum of other influences, 

 organic and inorganic; we must remember the time which 

 in any case is required for the modification of an instinct ; 

 and we must have proof that the instinct which is now in- 

 jurious in some percentage of cases, has long been highly 

 injurious in a large percentage of cases. I am not aware of 

 any instance where all these conditions have been fulfilled, 

 and where the species has not either been exterminated by 

 man, or the required modification of instinct has not actually 

 taken place. 



4. Mr. Darwin in the Appendix also alludes to the in- 

 jurious effects which frequently attend the exercise of the 



instiiiet of migration in certain animals. Thus, he says, the 



congregating of quadrupeds in Africa, and of the Passenger 

 Pigeons in America is detrimental to the animals, in conse- 

 quence "I their being thus readily followed by beasts of prey 



as well as by man. But when we. remember the enormous 

 numbers of both kinds of animals which thus congregate, 1 



cannot tee that any difficulty remains; for QOt only IS the 



