590 THE POPULAR SCIENCE MONTHLY. 



that the latter is prepared, even before indiyidual experience, to per- 

 form adjustive actions mechanically which, in previous generations, 

 were performed intelligently, Thio mode of origin of instincts has 

 been called by Mr. Lewes the " lapsing of intelligence," and it was 

 fully recognized by Mr. Darwin as a factor in the formation of in- 

 stinct. 



The Darwinian theory of instinct, then, attributes the evolution of 

 instincts to these two causes acting either singly or in combination — 

 natural selection and lapsing intelligence. I shall now proceed to ad- 

 duce some of the more important facts and considerations which, to 

 the best of my judgment, support this theory, and show it to be by 

 far the most comprehensive and satisfactory explanation of the phe- 

 nomena which has hitherto been propounded. 



That many instincts must have owed their origin and development 

 to natural selection exclusively is, I think, rendered evident by the fol- 

 lowing general considerations : 



1. Considering the great importance of instincts to species, we are 

 prepared to expect that they must be in large part subject to the influ- 

 ence of natural selection. 2. Many instinctive actions are performed 

 by animals too low in the scale to admit of our supposing that the ad- 

 justments which are now instinctive can ever have been intelligent. 

 3. Among the higher animals instinctive actions are performed at an 

 age before intelligence, or the power of learning by individual experi- 

 ence, has begun to assert itself 4. Many instincts, as we now find 

 them, are of a kind which, although performed by intelligent animals 

 at a matured age, yet can obviously never have been originated by in- 

 telligent observation. Take, for instance, the instinct 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 incu- 

 bating 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 gradu- 

 ally became warm-blooded, no doubt this latter function became of 

 more and more importance to incubation. Consequently, those indi- 

 viduals which most constantly cuddled their eggs would develop most 

 progeny, and so the incubating instinct would be developed by natu- 

 ral 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 intelligent, 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 domes- 



