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POPULAR SCIENCE MONTHLY. 



SCIENTIFIC LITERATURE. 



ZOOLOGY. 

 A plausible explanation of the oc- 

 currence of peculiarities of structure 

 and coloration in the males of many 

 animals, both vertebrate and inverte- 

 brate, was first given by Darwin in 

 his theory of sexual selection. Objec- 

 tions have been raised, however, to 

 that portion of the theory which con- 

 cerned ornamental peculiarities on the 

 ground that the existence of an es- 

 thetic sense sufficiently acute to ac- 

 count for the minute and complex de- 

 tails of coloration is in many cases 

 improbable, and from time to time 

 other theories have been advanced 

 which sought to avoid this difficulty. 

 Among these may be mentioned the 

 theory of Wallace, to the effect that 

 the greater ornamentation of the male 

 is due to his 'surplus of vitality'; that 

 of von Kennel, which is essentially a 

 negative statement of Wallace's, hold- 

 ing that the drain upon the vitality of 

 the female in the production of ova 

 prevents the full fruition of develop- 

 ment seen in the males; and the sacri- 

 ficial theory of Jager and Stolzmann, 

 according to which the brilliancy or 

 excessive development of the male con- 

 duces to his destruction whereby the 

 female is indirectly protected and the 

 male is removed from competition with 

 her in the struggle for nourishment. 



But all these theories are open to 

 the criticism either that they are too 

 general or that they fail to explain the 

 origin of the sexual peculiarities, and, 



recently, Professor J. T. Cunningham, 

 in his 'Sexual Dimorphism in the Ani- 

 mal Kingdom' (A. and C. Black, 

 1900), has endeavored to avoid both 

 these objections by discarding natural 

 selection in all its forms and relying 

 upon the Lamarckian hypothesis. He 

 regards secondary sexual characters as 

 being due to the inheritance of the 

 effects of definite mechanical and phys- 

 iological irritations, and endeavors to 

 correlate the peculiarities of various 

 species with their habits. Thus he 

 explains the mane of the lion not as a 

 protection, but as the result of the lo- 

 cal irritation of the skin due to the 

 habit possessed by fighting lions of 

 seizing one another by the nape of the 

 neck; the coloration and furrowing 

 of the cheek of the mandrill are due 

 to the inheritance of irritations and 

 injuries inflicted by the males in com- 

 bat; the plumes of the birds of para- 

 dise have reached their extensive de- 

 velopment by having been erected dur- 

 ing sexual excitement and so stimu- 

 lated to special growth through many 

 generations, and the naked head and 

 neck of the turkey-cock and his wat- 

 tles represent 'the inherited scars of 

 a long line of pugnacious ancestors.' 

 These examples, and they are by no 

 means extreme, may serve to indicate 

 the general tenor of Professor Cun- 

 ningham's argument, and it seems more 

 than doubtful if he has strengthened 

 the Lamarckian position or provided 

 valid evidence for the overthrowal of 

 the theory of sexual selection. 



