FIVE LINKS TO THE CHAIN 61 



some members of each species are different enough from the 

 others to survive in spite of threatened destruction. In other 

 words, he tells us that it is the fit who survive. This, then, is 

 the fourth link to the growing chain. 



See how this law works itself out. Some creatures have 

 longer legs and are therefore better fitted than their mates to 

 run away when danger threatens. Some have stronger claws 

 with which to kill the foe before being killed themselves. 

 Some have keener eyesight with which to discover danger 

 or to sight it from a distance and to escape it. Some have 

 keener scent with which to trace both food and danger. Some 

 can live longer than others when deprived of water. Some can 

 survive a famine where others die in the midst of it. 



Thus, in one way and another, in every group of animals, 

 when the critical moment comes, certain individuals are better 

 fitted to survive than are their neighbors. This does on no 

 account mean that the fittest are always the largest, the 

 tallest, the keenest-eyed, the bravest, the strongest, or the 

 longest-legged. Certainly not. The huge animals of South 

 America were bigger than any of those that crowded them 

 out ; English sparrows of the United States are smaller than 

 bluebirds, swallows, robins, the purple martin, and other birds 

 that please us ; but the smaller sparrow attacks the larger 

 birds, takes up their nesting places, destroys their eggs, and 

 finally succeeds in driving them from our villages. 



During heavy storms it is the birds with small bodies and 

 strong legs and wings that survive, while birds with large 

 bodies and small wings die in greatest numbers. 



Judging by appearance, certain animals the donkey, for 

 example were better fitted to survive when their ears were 

 large. It was different with moles. Living and working 

 underground as they did, ears were a nuisance ; they got in 



