SEXUAL COLOUR 83 



explains the dull colour of females but not 

 the brilliant colour of males. 



Emery's theory of the origin of secondary 

 sexual characters as mono-sexual sports may 

 explain their origin, although there appears 

 to be little evidence of this, but makes no 

 attempt to define the cause of these differ- 

 ences ; or assumes that the sport is retained 

 because and when it fits the environment 

 better than the old type. 



Those who believe in the transmission of ac- 

 quired characters look upon secondary sexual 

 characters as adaptations and due to the 

 stimulation of parts through use. Controlled 

 natural selection accounts for both the origin 

 and purpose of secondary sexual characters 

 in the following way. Males are more con- 

 spicuous in nature than females : males are 

 less valuable than females. Males and females 

 are associated together during life, and especi- 

 ally during the breeding season when the 

 difference in colour is greatest, and when their 

 difference in value is highest : therefore accord- 

 ing to the theory, the conspicuous colour of 

 the male serves to control natural selection 

 in such a way that the less valuable male 

 will be killed in preference to the more 

 valuable female. 



