40 CHARLES DARWIN 



throughout the greater part of geological time, essentially 

 tropical conditions existed unbroken over the whole 

 surface of the entire earth, from the Antarctic continent 

 to the shores of Greenland ; so that some immediate 

 acquaintance at least with the equatorial world is of 

 immense value to the philosophical naturalist for the 

 sake of the analogies it inevitably suggests ; and it is a 

 significant fact that almost all those great and fruitful 

 thinkers who in our own time have done good work in 

 the wider combination of biological facts have themselves 

 passed a considerable number of years in investigating 

 the conditions of tropical nature. Europe and England 

 are at the ends of the earth ; the tropics are biological 

 head-quarters. The equatorial zone is therefore the 

 true school for the historian of life in its more universal 

 and lasting aspects. 



Nor was that all. The particular countries visited 

 by the ' Beagle ' during the course of her long and 

 varied cruise happened to be exactly such as were 

 naturally best adapted for bringing out the latent po- 

 tentialities of Darwin's mind, and suggesting to his 

 active and receptive brain those deep problems of life 

 and its environment which he afterwards wrought out 

 with such subtle skill and such consummate patience 

 in the ' Origin of Species ' and the ' Descent of Man.' 

 The Cape de Verdes, and the other Atlantic islands, 

 with their scanty population of plants and animals, 

 composed for the most part of waifs and strays drifted 

 to their barren rocks by ocean currents, or blown out 

 helplessly to sea by heavy winds ; Brazil, with its 

 marvellous contrasting wealth of tropical luxuriance 

 and self-strangling fertility, a new province of inter- 



