144 DARWINISM AND THE PROBLEMS OF LIFE 



salamanders ; partly because the animals themselves are 

 rare. Natural selection does not provide for exceptional 

 cases; it only brings about adaptations that meet average 

 needs. A character can only be preserved when the 

 majority of the animals that did not possess it would 

 come to grief on that account. When a particular 

 danger only threatens a species now and again, the 

 animal that escapes it through some peculiar character- 

 istic will have no prospect of bringing this to predominate 

 in the species generally. The characteristic in question 

 will soon disappear owing to crossing with others ; while 

 the majority, which do not possess it, will survive, 

 because the danger is too infrequent to cause it to be 

 selected. When we find in the animals that they only 

 react by adaptations against dangers that are common 

 in their life, this is an excellent proof of the operation 

 of natural selection. 



We shall make the acquaintance in later chapters of 

 other animals that have a high power of regeneration, 

 but will for the moment cast another rapid glance at the 

 mammals and birds. If we bring before our minds the 

 enemies of the various species of these two classes, 

 their methods of attack, we see at once why they 

 generally have no faculty of regeneration. It is true 

 that the beak may be reproduced in the bird, and it is 

 this especially that is exposed to injury, as it is the 

 main implement and the weapon of the inhabitant of 

 the air. Further, the skin can be regenerated in 

 mammals ; and if a wound we have received were not 

 closed by scar-tissue, an infection by bacilli would 

 inevitably follow. And when we consider the absence 



