I900.] 177 



SECONDARY SEXUAL CHARACTERS. 



Sexual Dimorphism in the Animal King^dom, a Theory of 

 the Evolution of Secondary and Sexual Characters. By 



J. T. Cunningham, m.a. Londou : A. aud C. Black, 1900 : Svo, 

 pp. xi. & 310. Price, 12s. 6d, 



To criticise is one thing, to construct another. In this book, Mr. 

 Cunningham, whose criticisms of the Wallacian denial of the inheritance 

 of acquired characters have been so efficacious in repelling a lodgment 

 by the followers of Weismann on debateable ground, has himself 

 attempted to occupy it and to build thereon a theory of the application 

 of the transmission of acquired characters to the secondary sexual 

 characters of animals. To do this he has given us a very interesting, if 

 not quite exhaustive account of these characters with many new facts, 

 and this part of his book will, I think, give it a permanent value. But 

 I feel sure that for those of us who are in the same camp as Mr. 

 Cunningham, the better part for the present is to aim at keeping the 

 ground clear, rather than to put up works and push forward wxak forces 

 which will but give fresh occasion for the advances of our leading 

 opponents ; while their inevitable destruction will strengthen the idea 

 prevailing among the enlightened laity, like Mr. Balfour and Mr. Kidd, 

 that the views held by Charles Darwin are now exploded. 



As follows from what we have just said, the author seeks to demonstrate 

 that secondary sexual characters are the results of the response of 

 the organism to stimulation, either from within or without. Thus, the 

 growth of the beard in Primates is " due to the stimulation of the growth 

 of the hair by teeth or nails in the combats of mature males ;" but on 

 the next page we find: "What is wanted is evidence concerning the 

 influence of mechanical irritation of the hair follicles on the growth of 

 the hair." The probable cause of the loss of the body hair is traced to 

 the wearing of clothes. " In all communities the women pay more 

 attention to the wearing of clothes than men, and this agrees with the 

 fact that women, as a rule, have less hair." In illustration he cites the 

 fact that young animals, like mice and rabbits, born into close warm 

 nests, are naked, and suggests that the carrying of the children on the 

 mother's back, in a fold of some garment, in primitive times, was the 

 cause of the denudation of the infant. On the contrary, the Mandrill is 

 supposed to have acquired the bare grooved patches of its face, by the 

 males scoring one another in their fights for the rarer females, while 

 their coloration elsewhere is explained by the attentions of their mates. 

 Again, the mane of the male Baboons and of the Lion, like the plumes 

 of cock birds, are supposed to have been gained by the habit of these 

 animals of raising them when excited. 



The development of vocal sacs in the males of mammals, birds, and 

 frogs is more obviously traced to the yielding of the walls of the cavities 



