296 



THE ORIGiy OF SPECIES 



stinetp. I have attempted to show how much light the 

 principle of gradation throws on the admirable architect- 

 ural powers of the hive-bee. Habit no doubt often comes 

 into play in modifying instincts; but it certainly is not 

 indispensable, as we see in the case of neuter insects, 

 which leave no progeny to inherit the effects of long- 

 continued habit. On the view of all the species of the 

 same genus having descended from a common parent, and 

 having inherited much in common, we can understand 

 how it is that allied species, when placed under widely 

 different conditions of life, yet follow nearly the same 

 instincts; why the thrushes of tropical and temperate 

 South America, for instance, line their nests with mud 

 like our British species. On the view of instincts having 

 been slowly acquired through natural selection, we need 

 not marvel at some instincts being not perfect and liable 

 to mistakes, and at man}' instincts causing other animals 

 to suffer. 



If species be only well-marked and permanentvari- 

 \ eties, we can at once see why their crossed offspring 

 should follow the same complex laws in their degrees 

 Vand kinds of resemblance to their parents — in being ab- 

 V sorbed into each other by successive crosses, and in other 

 such points — as do the crossed offspring of acknowledged 

 varieties. This similarity would be a strange fact, if spe- 

 cies had been independently created and varieties had 

 been produced through secondary laws. 



If we admit that the geological record is imperfect 

 to an extreme degree, then the facts which the record 

 does give strongly support the theory of descent with 

 modification. New species have come on the stagu slowly 

 and at successive intervals; and the amount of change, 



