THE DARWINIAN THEORY OF INSTINCT. 591 



tication, we constantly meet with individual peculiarities of disposition 

 and of habit, which in themselves are utterly meaningless, and there- 

 fore quite useless. But it is easy to see that, if, among a number of 

 such meaningless or fortuitous psychological variations, any one arises 

 which happens to be of use, this variation would be seized upon, inten- 

 sified, and fostered by natural selection, just as in the analogous case 

 of structures. Moreover, there is evidence that such fortuitous varia- 

 tions in the psychology of animals (whether useless or accidentally use- 

 ful) are frequently inherited, so as to become distinctive, not merely of 

 individuals, but of races or strains. Thus, among Mr. Darwin's manu- 

 scripts, I find a letter from Mr. Thwaites, under the date of 1860, say- 

 ing that all his domestic ducks in Ceylon had quite lost their natural 

 instincts with regard to water, which they would never enter unless 

 driven, and that, when the young birds were thus compelled to enter 

 the water, they had to be quickly taken out again to prevent them 

 from drowning. Mr. Thwaites adds that this peculiarity only oc- 

 curs in one particular breed. Tumbler-pigeons instinctively tumbling, 

 pouter-pigeons instinctively pouting, etc., are further illustrations of 

 the same general fact. 



Coming now to instincts developed by lapsing intelligence, I have 

 already alluded to the acquisition of an hereditary fear of man as an 

 instance of this class. Now, not only may the hereditary fear of man 

 be thus acquired through the observation of ancestors — and this even 

 to the extent of knowing by instinct what constitutes safe distance 

 from fire-arms — but, conversely, when fully formed it may again be 

 lost by disuse. Thus, there is no animal more wild, or difficult to 

 tame, than the young of the wild rabbit ; while there is no animal 

 more tame than the young of the domestic rabbit. And the same 

 remark applies, though in a somewhat lesser degree, to the young of 

 the wild and of the domestic duck. For, according to Dr. Rae, "if 

 the eggs of a wild duck are placed with those of a tame duck under a 

 hen to be hatched, the ducklings from the former, on the very day 

 they leave the egg, will immediately endeavor to hide themselves, or 

 take to the water, if there be any water, should any one approach, 

 while the young from the tame duck's eggs will show little or no 

 alarm." Now, as neither rabbits nor ducks are likely to have been 

 selected by man to breed from on account of tameness, we may set 

 down the loss of wildness in the domestic breeds to the uncompounded 

 effects of hereditary memory of man as a harmless animal, just as we 

 attributed the original acquisition of instinctive wildness to the heredi- 

 tary memory of man as a dangerous animal ; in neither case can we 

 suppose that the principle of selection has operated in any considerable 

 degree. 



Thus far, for the sake of clearness, I have dealt separately with 

 these two factors in the formation of instinct — natural selection and 

 lapsing intelligence — and have sought to show that either of them 



