190 DISCOVERY CH. 



seventy-two survived, while sixty-two perished. On 

 comparing the survivors with the eliminated individuals, 

 very appreciable differences were found between them. 

 Nearly all the birds which were longer than the average 

 were among the dead, and the two shortest birds of the 

 whole number collected also perished. Natural selection 

 was, in fact, found to be most destructive of those birds 

 which departed most from the normal type. The general 

 conclusion drawn from the measurements of the birds 

 which survived or were eliminated was that the next 

 generation of sparrows in the storm-swept area would 

 be shorter in length, weigh less, have longer legs and a 

 greater brain capacity than the former generation. 



Of course, many more observations of a similar kind 

 are required before a definite statement could be made 

 of the structural forms favourable or unfavourable to 

 survival. The measurements are valuable so far as 

 they go, but there may have been some characteristics 

 which could not be measured and yet were really the 

 determining causes of survival or death. It is, however, 

 safe to conclude that in general, both with plants and 

 animals, individuals which depart most from the normal 

 type are the first to be eliminated. Even with the human 

 race, we find genius dying early from neglect, while 

 mediocrity treads contentedly along a primrose path. 

 From the point of view of survival, it is just as bad to 

 be in advance of the time as behind it. 



Wallace arrived independently at the solution of the 

 problem of evolution by means of the process of natural 

 selection, and, like Darwin, he was led to it by Malthus's 

 essay. It was Darwin's Journal, published in 1845, 

 and read by Wallace at the age of twenty-three, which 

 determined him to invite H. W. Bates to accompany 

 him on his journey to the Amazon and Rio Negro, 



