108 Evolution and Adaptation 



indeed I am not aware that this has ever been disputed. It 

 is immaterial for us whether a multitude of doubtful forms be 

 called species or subspecies or varieties ; what rank, for in- 

 stance, the two or three hundred doubtful forms of British 

 plants are entitled to hold, if the existence of any well-marked 

 varieties be admitted. But the mere existence of individual 

 variability and of some few well-marked varieties, though 

 necessary as the foundation for the work, helps us but little 

 in understanding how species arise in nature. How have all 

 those exquisite adaptions of one part of the organization to 

 another part, and to the conditions of life, and of one organic 

 being to another being, been perfected ? We see these beau- 

 tiful coadaptions most plainly in the woodpecker and the 

 mistletoe ; and only a little less plainly in the humblest 

 parasite which clings to the hairs of a quadruped or feathers 

 of a bird ; in the structure of the beetle which dives through 

 the water; in the plumed seed which is wafted by the 

 gentlest breeze ; in short, we see beautiful adaptions 

 everywhere and in every part of the organic world. 



" Again, it may be asked, how is it that varieties, which I 

 have called incipient species, become ultimately converted 

 into good and distinct species, which in most cases obviously 

 differ from each other far more than do the varieties of the 

 same species ? How do those groups of species, which con- 

 stitute what are called distinct genera, and which differ from 

 each other more than do the species of the same genus, arise ? 

 All these results, as we shall more fully see in the next 

 chapter, follow from the struggle for life. Owing to this 

 struggle, variations, however slight and from whatever cause 

 proceeding, if they be in any degree profitable to the individ- 

 uals of a species, in their infinitely complex relations to other 

 organic beings and to their physical conditions of life, will 

 tend to the preservation of such individuals, and will gener- 

 ally be inherited by the offspring. The offspring, also, will 

 thus have a better chance of surviving, for, of the many 



