4 EVOLUTION. 



main process through which the evolution of forms 

 takes place. More organisms come into life than 

 the means of subsistence can support. This leads to 

 a struggle for existence. There is some variety in 

 the forms of individuals of each species of plants and 

 animals, and those possessing the variations most 

 suited to their conditions are enabled to survive, 

 while those less adapted to the circumstances perish. 

 This is called the survival of the fittest. These indi- 

 viduals reproduce in their offspring the variations 

 that have benefited them, and new variations occur, 

 those that are useful being perpetuated. 



Thus there is a continual divergence from the 

 parent stock, wherever there is a change of surround- 

 ing conditions that makes variations serviceable to 

 existence. When these variations are long continued 

 they form new species. But where there is no 

 change in the circumstances of life, and the means 

 of existence are abundant, there is little or no change 

 in the forms of life. This process by which nature 

 selects the forms best suited to their surroundings is 

 called by Darwin Natural Selection. 



Sexual Selection, 



Darwin notes another cause of the variation of 

 species, which he calls Sexual Selection. The male 

 animals battle for the possession of the females. The 

 strongest wins, and transmits his peculiarities to his 

 descendants. In many cases the female selects the 



