THE EVOLUTION OF SPECIES 149 



without number, but if the ground be already fully and 

 strongly held, they cannot live and grow. The multi- 

 plication of animals is limited by the same principle. 

 Over-population, excessive increase of any species, pro- 

 duces a struggle for existence. Seeds and plants contend 

 for a place in the ground and for the nourishment it 

 yields. Animals contend for food and other necessaries 

 of life. The strongest varieties prevail. They assert 

 their superiority, maintain their ground, seize the food. 

 They live and flourish and multiply. They survive, and 

 transmit their characteristics to their offspring. This 

 is the law variously denominated : The struggle for 

 existence, the survival of the fittest, or natural selection, 

 by which nature selects and hands forward all improve- 

 ments, and so advances. 



5. The law of unceasing change of environment. Even 

 now no year or season is like another. There are seasons 

 in which the greatest strain is put on the existence of 

 various species, in which the struggle is of terrible in- 

 tensity, and the weakest perish. 



6. Past time has been to all intents and purposes 

 infinite. Many millions of years have passed since evolu- 

 tion began, since the first forms of life were quickened. 

 Ample time and opportunities have been afforded for the 

 advances made. Hence it is probable that the existing 

 species of plants and animals have been evolved from a 

 few primitive and simple forms of life, or probably from 

 one form alone. 



According to the theory of evolution, there was a time 

 when life existed not on the earth. Ey chemical action, 

 by a concourse of molecules of a very peculiar and 

 complex nature, a concourse taking place in very peculiar 

 and complex circumstances, such as no experiment can 

 now discover, protoplasm came into being, and life was 



