1884.] on the Darwinian Theory of Instinct. 135 



of incubation. It is quite impossible that any animal, prior to 

 individual or ancestral experience, can have kept its eggs warm with 

 the intelligent purpose of developing their contents ; so we can only 

 suppose that the incubating instinct began in some such form as we 

 now see it in the spider, where the object of the process is protection, 

 as distinguished from the imparting of heat. But incidental to such 

 protection in the case of a warm-blooded animal is the imparting of 

 heat, and as animals gradually became warm-blooded, no doubt this 

 latter function became of more and more importance to incubation. 

 Consequently, those individuals which most constantly cuddled their 

 eggs would develop most progeny, and so the incubating instinct 

 would be developed by natural selection without there ever having 

 been any intelligence in the matter. 



From these four general considerations, therefore, we may conclude 

 (without waiting to give special illustrations of each) that one mode 

 of origin of instincts consists in natural selection, or survival of the 

 fittest, continuously preserving actions which, although never intelli- 

 gent, yet happen to have been of benefit to the animals which first 

 chanced to perform them. Among animals, both in a state of nature 

 and domestication, we constantly meet with individual peculiarities 

 of disposition and of habit, which in themselves are utterly meaning- 

 less, and therefore 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, intensified, and fostered by natural selection, just as in the 

 analogous case of structures. Moreover there is evidence that such 

 fortuitous variations in the psychology of animals (whether useless or 

 accidentally useful) are frequently inherited, so as to become distinc- 

 tive, not merely of individuals, but of races or strains. Thus, among 

 Mr. Darwin's manuscripts I find a letter from Mr. Thwaites under 

 the date 1860, saying 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 pecu- 

 liarity only occurs in one particular breed. Tumbler pigeons in- 

 stinctively tumbling, pouter-pigeons instinctively pouting, &c., 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 



