6o TJie Descent of Man. }'art 



have evidence tfiai mutilations occasionally produce an inherited 

 effect, 94 it is not very improbable that in short-tailed monkeys, the 

 projecting part of the tail, being functionally useless, should after 

 many generations have become rudimentary and distorted, from 

 being continually rubbed and chafed. We see the projecting part in 

 this condition in the Macacus hrunneus, and absolutely aborted in 

 the M. ecaudatus and in several of the higher apes. Finally, then, 

 as far as we can judge, the tail has disappeared in man and the 

 anthropomorphous apes, owing to the terminal portion having 

 been injured by friction during a long lapse of time ; the basal 

 and embedded portion having been reduced and modified, so as 

 to become suitable to the erect or semi-erect position. 



I have now endeavoured to shew that some of the most 

 distinctive characters of man have in all probability been 

 acquired, either directly, or more commonly indirectly, through 

 natural selection. We should bear in mind that modifications 

 in structure or constitution, which do not serve to adapt an 

 organism to its habits of life, to the food which it consumes, or 

 passively to the surrounding conditions, cannot have been thus 

 acquired. We must not, however, be too confident in deciding 

 what modifications are of service to each being: we should 

 remember how little we know about the use of many parts, or 

 what changes in the blood or tissues may serve to fit an 

 organism for a new climate or new kinds of food. Nor must wo 

 forget the principle of correlation, by which, as Isidore Geoffroy 

 has shewn in the case of man, many strange deviations of 

 structure are tied together. Independently of correlation, a 

 change in one part often leads, through the increased or decreased 

 use of other parts, to other changes of a quite unexpected 

 nature. It is also well to reflect on such facts, as the wonderful 

 growth of galls on plants caused by the poison of an insect, and 

 on the remarkable changes of colour in the plumage of parrots 

 when fed on certain fishes, or inoculated with the poison of 

 toads; 95 for we can thus see that the fluids of the system, if 

 altered for some special purpose, might induce other changes. 

 We should especially bear in mind that modifications acquired 



64 I allude to Dr. Brown-Sequard's inherited effects of mot-mots biting 

 observations on the transmitted off the barbs of their own tail- 

 effect of an operation causing epi- feathers. See also on the general 

 lepsy in guinea-pigs, and likewise subject Variation of Animals and 

 more recently on the analogous Plants under Domestication,' vol. 

 effects of cutting the sympathetic ii., pp. 22-24. 



nerve in the neck. I shall hereafter 95 'The Variation of Animals and 



have occasion to refer to Mr. Salvin's Plants under Domestication,' vol. ii 



interest ng case of the apparently pp. 280, 282. 



