290 Habit and Instinct. 



led to the establishment of the transmission of acquired 

 characters ? If so, produce unquestionable and unim- 

 peachable evidence of the fact. 



This, however, is just what it is exceedingly difficult to 

 do. At first sight, for example, the nesting habit of the 

 house martin would appear to afford satisfactory evidence 

 of the conversion of an acquired habit into a congenital 

 instinct. But quite possibly it is the result of intelligent 

 adaptation through the influence of tradition. Our first 

 difficulty, then, is to prove conclusively that a given mode of 

 behaviour is truly congenital and instinctive, and not due 

 to the play of animal tradition. One or two further cases 

 which illustrate this difficulty may be given. Where 

 telegraph wires have been led across Scottish moors, 

 grouse have been killed in numbers by flying against them. 

 But after a season or two the destruction has ceased. 

 Have the young birds inherited the habit of so flying as 

 to avoid the wires ; or has the habit been handed down 

 by animal tradition ? The old birds are said to lead the 

 flocks ; and if they have either themselves been hurt 

 when they were young, or followed those who had so 

 learnt to avoid the wires, they would have acquired caution, 

 and thus lead their followers to be cautious. Hence a 

 habit of caution would be handed on by tradition. The 

 difficulty is represented in another form in the case of the 

 duck (Dendrocygna autumnalis), which is found in the well- 

 timbered region along the Eio Grande of Texas, at Lomita. 

 Since the river furnishes no sort of food, being cold and 

 muddy from the melting snows of the mountains whence it 

 flows, the duck adapts itself to circumstances and feeds 

 upon seeds and grain. It can alight on a stalk of growing 

 corn with the ease of a blackbird, and is quite at hom< 

 among the lofty trees where it makes its nest.* It woul< 

 * Nature, vol. xliv. p. 529. 



