THE STORY OF NINETEENTH-CENTURY SCIENCE 



somehow kept in check. Cogitating this thought, Dar- 

 win gained a new insight into the processes of nature. 

 He saw that in virtue of this tendency of each race of 

 beings to overpopulate the earth, the entire organic 

 world, animal and vegetable, must be in a state of 

 perpetual carnage and strife, individual against indi- 

 vidual, fighting for sustenance and life. 



That idea fully imagined, it becomes plain that a select- 

 ive influence is all the time at work in nature, since only 

 a few individuals, relatively, of each generation can come 

 to maturity, and these few must, naturally, be those 

 best fitted to battle with the particular circumstances 

 in the midst of which they are placed. In other words, 

 the individuals best adapted to their surroundings will, 

 on the average, be those that grow to maturity and 

 produce offspring. To these offspring will be trans- 

 mitted the favorable peculiarities. Thus these pecul- 

 iarities will become permanent, and nature will have 

 accomplished precisely what the human breeder is seen 

 to accomplish. Grant that organisms in a state of 

 nature vary, however slightly, one from another (which 

 is indubitable), and that such variations will be trans- 

 mitted by a parent to its offspring (which no one then 

 doubted); grant, further, that there is incessant strife 

 among the various organisms, so that only a small pro- 

 portion can come to maturity grant these things, said 

 Darwin, and we have an explanation of the preservation 

 of variations which leads on to the transmutation of 

 species themselves. 



This wonderful coign of vantage Darwin had reached 

 by 1839. Here was the full outline of his theory ; here 

 were the ideas which afterwards came to be embalmed 

 in familiar speech in the phrases " spontaneous varia- 



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