Ce. XXXVII.] 



EAPID INCREASE OF ANIMALS. 



317 



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may 



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and if. 



embrace 



gressive development explained in the first volume (Cliap. 



must 



nature 



may 



insight into them. But granting what is undeniable, that 

 there is a tendency in all animals and plants to possess 

 individual peculiarities by which they differ slightly from 

 their parents and from each other, are there not forces in 

 operation in the organic and inorganic world, Avhich, in the 



may 



more 



at length they constitute new species ? If there be such a 

 process in nature, it will most nearly resemble that kind of 



selection which has been called ^ unconscious,' and 



human 



moi 



effective in the long run than that which is intentional. 



Tendency 



%n 



>/ 



subsistence. — It has already been stated that if all the progeny 

 of each animal and plant which are born into the world were 



m 



the whole of the habitable land or water. 



Malthus lono' as 



o a 



man 



crease were not checked by scarcity of food, the earth would 

 soon fail to afford standing room for the descendants of a single 

 pair. The elephant, says Darwin, although reckoned the 

 slowest breeder of all known animals, would nevertheless so 

 multiply, if we assume that it only begins to have youno- when 

 thirty years old, and brings forth three pair between that age 

 and the age of ninety, that if all its descendants were to live 



term 



million 



descended from a 



single pair. 



In the severe struggle for existence which is always going 

 on, those varieties or species which have any even the slight- 

 est advantage over others inhabitincr the same district will be 



the survivors, 

 heat, moisture 



may 



B 



