PDF - Wallace Online

50 NATURAL SELECTION intions, when not accompanied by others that were unfavourable,would certainly survive. At one time a little step might bemade in this direction, at another time in that a change ofconditions might sometimes render useless that which it hadtaken ages to produce great and sudden physical modificationsmight often produce the extinction of a race just as itwas approaching perfection, and a hundred checks of whichwe can know nothing may have retarded the progress towardsperfect adaptation so that we can; hardly wonder at therebeing so few cases in which a completely successful result hasbeen attained as shown by the abundance and wide diffusionof the creatures so protected.Objection that Colour, as being dangerous, should not exist inNatureIt is as well here to reply to an objection that will nodoubt occur to many readers that if concealment is so usefulto all animals, and so easily brought about by variation andsurvival of the there fittest, ought to be no conspicuouslycolouredcreatures; and they will perhaps ask how weaccount for the brilliant birds, and painted snakes, andgorgeous insects that occur abundantly all over the world.It will be advisable to answer this question rather fully, inorder that we may be prepared to understand the phenomenaof " mimicry," which it is the special object of this chapter toillustrate and explain.The slightest observation of the life of animals will showus that they escape from their enemies and obtain theirin an infinite number of ways, and that their varied habitsand instincts are in every case adapted to the conditions oftheir existence. The porcupine and the hedgehog have adefensive armour that saves them from the attacks of mostanimals. The tortoise is not injured by the conspicuouscolours of his shell, because that shell is in most cases aneffectual protection to him. The skunks of North Americafind safety in their power of emitting an unbearably offensiveodour ;the beaver in its aquatic habits and solidly constructedabode. In some cases the chief danger to an animal occursat one particular period of its existence, and if that is guardedagainst its numbers can easily be maintained. This is the