60 THE ORIGIN OF SPECIES 



increase of the missel-thrush in parts of Scotland has caused the 

 decrease of the song-thrush. How frequently we hear of one spe- 

 cies of rat taking the place of another species under the most dif- 

 ferent climates! In Russia the small Asiatic cockroach has every- 

 where driven before it its great congener. In Australia the imported 

 hive-bee is rapidly exterminating the small, stingless native bee. 

 One species of charlock has been known to supplant another spe- 

 cies; and so in other cases. We can dimly see why the competition 

 should be most severe between allied forms, which fill nearly the 

 same place in the economy of nature; but probably in no one case 

 could we precisely say why one species has been victorious over 

 another in the great battle of life. 



A corollary of the highest importance may be deduced from the 

 foregoing remarks, namely, that the structure of every organic 

 being is related, in the most essential yet often hidden manner, to 

 that of all the other organic beings, with which it comes into com- 

 petition for food or residence, or from which it has to escape, or 

 on which it preys. This is obvious in the structure of the teeth 

 and talons of the tiger; and in that of the legs and claws of the 

 parasite which clings to the hair on the tiger's body. But in the 

 beautifully plumed seed of the dandelion, and in the flattened and 

 fringed legs of the water-beetle, the relation seems at first con- 

 fined to the elements of air and water. Yet the advantage of the 

 plumed seeds no doubt stands in the closest relation to the land 

 being already thickly clothed with other plants, so that the seeds 

 may be widely distributed and fall on unoccupied ground. In the 

 water-beetle, the structure of its legs, so well adapted for diving, 

 allows it to compete with other aquatic insects, to hunt for its own 

 prey, and to escape serving as prey to other animals. 



The store of nutriment laid up within the seeds of many plants 

 seems at first sight to have no sort of relation to other plants. But 

 from the strong growth of young plants produced from such seeds, 

 as pease and beans, when sown in the midst of long grass, it may 

 be suspected that the chief use of the nutriment in the seed is to 

 favor the growth of the seedlings, while struggling with other 

 plants growing vigorously all around. 



Look at a plant in the midst of its range! Why does it not 

 double or quadruple its numbers? We know that it can perfectly 

 well withstand a little more heat or cold, dampness or dryness, 

 for elsewhere it ranges into slightly hotter or colder, damper or 

 dryer districts. In this case we can clearly see that if we wish in 

 imagination to give the plant the power of increasing in numbers, 

 we should have to give it some advantage over its competitors, or 



