48 PHILOSOPHICAL NOTES ON 



begins his wanderings in oliedience to the impulse of his own will 

 his own pleasure or interest, proceeding forwards, to the right or 

 left, or even backwards, with longer or shorter pauses, and 

 starting at any particular time, it is obvious that the route taken 

 lies in the man himself, and is determined by his own particular 

 temperament. His judgment, experience, and inclination will 

 influence his course at each turn of his journey, as new circum- 

 stances arise. He will turn aside from a mountain which he 

 considers too lofty to be climbed ; he will incline to the right, if 

 this direction appears to afford a better passage over a swollen 

 stream ; he will rest when he reaches a pleasant halting-place, and 

 will hurry on when he knows that enemies beset him. And in 

 spite of the perfectly free choice open to him, the course he takes 

 is in fact decided by both the place and time of his starting and 

 by circumstances, which — always occurring at every part of the 

 journey — impel him one way or the other; and if all the factors 

 could be ascertained in the minutest detail, his course could be 

 predicted from the beghining. 



" Such a traveller represents a species, and his route 

 corresponds with the changes, which are induced in it by natural 

 selection.* The changes are determined by the physical nature 

 of the species, and by the conditions of life by which it is 

 surrounded at any given time. A number of different changes may 

 occur at every point, but that one will actually develop which is the 

 most useful, under existing external conditions. The species will 

 remain unaltered as long as it is in perfect equilibrium with its 

 surroundings, and as soon as this equilibrium is disturbed it will 

 commence to change. f It may also happen that, in spite of all 

 the pressure of competing species, no further change occurs 

 because no one of the innumerable very slight changes, which are 

 alone possible at any one time, can help in the struggle ; just as 

 the traveller who is followed by an overpowering enemy, is 

 compelled to succumb when he has been driven down to the sea. 

 A boat alone could save him, without it he must perish ; and so 

 it sometimes happens that a species can only be saved from 



♦ By natural selection is meant the course most suited to the well-being 

 and continued existence of the individual at that time, 

 f That IS a new selection will begin to occur. 



