228 DIVERSIONS OF A NATURALIST 



highly endowed and successful forms on account of their 

 dominance and power of spreading into new conditions, 

 are even more likely than less highly developed kinds 

 to retain concealed defects — disharmonies which do not 

 lead to the destruction of the species, but occasionally 

 cause strange embarrassment to it until they are, possibly 

 in the long process of ages, got rid of by the slow opera- 

 tion of selection and survival of those individuals in 

 which the injurious character varies in the direction of 

 diminution and ultimate disappearance. 



In man (owing, apparently, to the rapid rate at which 

 he has been carried along towards dominance over the 

 whole face of the globe by the development of his in- 

 telligence) the bodily structure has failed to keep pace 

 with and to become perfected, " trimmed up," and com- 

 pletely adapted to, the newly-acquired habits which his 

 increasing intelligence has forced on him. His " wisdom 

 teeth " are " disharmonies." They are now useless and 

 dwindled, weak spots open to the attacks of disease — 

 since they are no longer needed for grinding coarse 

 vegetable food, and are consequently no longer kept (by 

 the speedy death of those individuals in whom they are 

 small) at the full original size and efficiency seen in the 

 apes. His large intestine is a " disharmony " not yet 

 got rid of by natural selection, although no longer useful, 

 but, on the contrary, the seat of poisonous putrefactioh 

 and absorption of such poisons. His tail — a few small 

 vertebrae beneath the skin — is absolutely useless, and 

 occasionally the seat of dangerous injury or disease. 

 Tails very generally are liable to become useless in the 

 descendants of animals in which they were invaluable as 

 " fly-brushes " (cattle, horses, etc.), as prehensible organs 

 (American monkeys), as concealing cloaks (South 

 American ant-eater), as aids to swimming or flying, or 



