THE MOTH AND THE CANDLE 227 



changing world, many of them have retained structures 

 or chemical constitutions which once were useful but 

 now are useless, or even positively injurious. Even 

 injurious structures or behaviours may be retained and 

 inherited by a species of plant or animal, if, on the 

 whole, the other accompanying modifications of structure 

 are valuable — that is, of " life-saving " value, so that, 

 " on the whole," the race is favoured by selection in the 

 struggle for existence. 



In species which have but lately acquired dominance 

 or are brought by their success into novel conditions, we 

 may, and do, find old structures and behaviours still per- 

 sisting which are injurious, not yet, as it were, " cleaned 

 up " and got rid of as they would be in the course of 

 further long periods of selection. Such species become 

 established, and may even acquire a definite stability, 

 because the injurious structures or behaviours which they 

 have retained are of little or no account as compared 

 with the other advantageous characters which the species 

 have developed. The term " disharmonies " is applied to 

 such injurious characters, consisting in a certain want of 

 harmony (in minor respects) between the structure of an 

 organism and the conditions in which, nevertheless, it 

 thrives. 



I 



Such species, imperfect because of their " dishar- 

 monies," are an illustration of the fact that Nature 

 herself, in matters relating to living things, is not averse 

 to compromise. Nature sets the example of toleration. 

 Toleration may be defended on the ground that it is 

 the biological method. Nature, though stern and in- 

 exorable as to essentials, yet accepts the faults and 

 defects of some of her children because of the virtues 

 and excellences which accompany them. The most 



