DARWIN'S WANDER- YEARS 51 



The Principle of Population,' which (as we know 

 from his own pen) formed a cardinal point in the great 

 biologist's mental development. It runs as follows in 

 the published journal : ' ' We do not steadily bear in 

 mind how profoundly ignorant we are of the condi- 

 tions of existence of every animal ; nor do we always 

 remember that some check is constantly preventing tho 

 too rapid increase of every organised being left in a 

 state of nature. The supply of food, on an average, 

 remains constant ; yet the tendency in every animal to 

 increase by propagation is geometrical, and its sur- 

 prising effects have nowhere been more astonishingly 

 shown than in the case of the European animals run 

 wild during the last few centuries in America. Every 

 animal in a state of nature regularly breeds ; yet in a 

 species long established any great increase in numbers 

 is obviously impossible, and must be checked by some 

 means.' Aut Malthus ant Diabolus. And surely here, 

 if anywhere at all, we tremble on the very verge of 

 natural selection. 



It would be impossible to follow young Darwin in 

 detail through his journey to Buenos Ayres, and up the 

 Parana to Santa Fe, which occupied the autumn of 1833. 

 In the succeeding year he visited Patagonia and the 

 Falkland Islands, having previously made his first ac- 

 quaintance with savage life among the naked Fue- 

 gians of the extreme southern point of the continent. 

 Some of these interesting natives, taken to England by 



1 The full narrative was first given to the world in 1839, some 

 three years after Darwin's return to England, so that much of it 

 evidently represents the results of his maturer thinking and reading 

 on the facts collected during his journey round the world. 



