Chap. VII. OF NATURAL SELECTION. 231 



of the fact. I have, therefore, discussed this case, at some little 

 but wholly insuniciout length, in order to show tlio power of nat- 

 ural selection, and likewise because this is by far the most serious 

 special dillieulty which my theory has encountered. The case, 

 also, is very intercstinir, as it proves that with animals, as with 

 plants, any amount of modification may be cUc'cted ])y the ac- 

 cumulation o( numerous, slight, spontaneous variations, which 

 are in any way jirolitable, without exercise or hal)it havini^ 

 been brouf^ht into play. For peculiar hal^its confined to the 

 workers or sterile females, however long they mif^ht be fol- 

 lowed, could not possibly affect the males and fertUe female, 

 which alone leave descendants. I am surprised that no one 

 has hitherto advanced this demonstrative case of neuter insects, 

 against the well-known doctrine of inherited habit, as advanced 

 by Lamarck. 



iSummari/. 



I have endeavored in this chapter briefly to show that the 

 mental qualities of our domestic animals vary, and that the vari- 

 ations are inlierited. Still more briefly I have attempted to show 

 that instincts A'ary slightly in a state of nature. No one will 

 dispute that instincts are of the highest importance to each 

 animal. Therefore there is no real diiliculty, under changing 

 conditions of life, in natural selection accumulating to any ex- 

 tent slight modifications of instinct which are in any way use- 

 ful. In some cases habit or use, and disuse, have proliably come 

 into play. I do not pretend that the facts given in this chapter 

 strengthen in any great degree my theory ; but none of the 

 cases of diiliculty, to the best of my judgment, annihilate it. 

 On the other hand, the fact that instincts are not always ab- 

 solutely perfect, and are liable to'mistakes ; that no instinct 

 can be shown to have been produced for the good of other 

 animals, tliough animals take advantage of the instincts of 

 others; that tlie canon in natural history of " Natura non facit 

 saltuin,"isap]ili(able to instincts as well as to corporeal struct- 

 ure, and is plainly explicable on the foregoing views, but is 

 otherwise inexplicable — all tend to corroborate the theory of 

 natural selection. 



This theory is, also, strengthened by some few other facts in 

 regard to instincts ; as by that common case of closely-allied, 

 but distinct, species, when inhabiting distant parts of the 

 world and living under considerably diffcM-ent conditions of 

 lifCj yet often retaining nearly the same instincts. For instance, 



