MY SOMALI BOOK 219 



sufficiently general application to be worth considering 

 in this connection are to be found in the theories 

 of sexual selection and of recognition marks (warning 

 colouration and mimicry being included under pro- 

 tective colouration). 



Darwin ascribes to the influence of sexual selection 

 many instances of striking colours or markings that 

 Wallace and others have considered to be protective or 

 useful for mutual recognition. He believed that 

 brilliant colourings or other ornamental characteristics, 

 originally acquired or developed b}^ the male through 

 sexual selection, were often transmitted to both sexes, 

 and he thus accounts for the colouring in many cases 

 where the sexes are alike ; the zebra's beautiful coat, 

 for instance, although in none of the Equidce do the 

 sexes differ in colour. The difficulty that in many 

 cases the male does not share his ornamentations with 

 his mate, he is unable to solve, but puts aside as one of 

 the unexplained peculiarities of the unquestionabh^ 

 complex laws of heredity. Though not perhaps in- 

 surmountable, it remains a difficulty. 



There is another and more important difficulty 

 which Darwin himself realises and finds it difficult to 

 answer. In his own words, " If we admit that coloured 

 spots and stripes were first acquired as ornaments, 

 how comes it that so many existing deer, the 

 descendants of an aboriginally spotted animal, and all 

 the species of pigs and tapirs, the descendants of an 

 aboriginally striped animal, have lost in their adult 

 state their former ornaments ? " The only answer 

 he has to give is that with an increase in size and 

 number of the carnivora during the Tertiary period, 



