1/8 SCIENCE SKETCHES. 



numerous, and some of them are imperfectly un- 

 derstood. One of these — and in Mr. Darwin's 

 view, the predominant one — has been the survi- 

 val of the fittest in the struggle for existence. 



I cannot in the limits of this address illustrate in 

 detail what is implied in that which has been called 

 "natural selection" by Mr. Darwin, and by Mr. 

 Spencer the " survival of the fittest." In Mr. 

 Darwin's words, — 



" A struggle for existence inevitably follows from the high 

 rate at which all organic beings tend to increase. Every 

 being which during its lifetime produces several eggs or 

 seeds must suffer destruction during some period of its life 

 and during some season or occasional year ; otherwise, on 

 the principle of geometrical increase, its numbers would 

 quickly become so inordinately great that no country could 

 support the product. Hence, as more individuals are pro- 

 duced than can possibly survive, there must in every case 

 be a struggle for existence, either one individual with others 

 of the same species, or with the individuals of different 

 species, or with the physical conditions of life. Although 

 some species may be increasing in numbers, all cannot do 

 so, for the world would not hold them." 



A calculation has been lately made that at the 

 normal rate of increase from a pair of English 

 sparrows, if none were to die except of old age, 

 it would take but twenty years to give one sparrow 

 to every square inch of the State of Indiana. But 

 such increase is actually impossible ; for more than 

 a hundred other species of resident birds are dis- 

 puting the same territory, and there cannot be place 

 or food for all. With such conditions, the struggle 

 for existence between sparrow and sparrow, and 



