EVOLUTION OF THE COLORS OF BIRDS. 69 



color of this race was produced from brown or gray an- 

 cestors. It is found that the male averages considerably 

 darker than the female, although females may be found 

 as dark as the lightest males. This is in accordance with 

 the principle enunciated by Geddes and Thomson, that 

 the tendency of the male is katabolic, of the female 

 anabolic. The surplus of energy of the male would be 

 expended in pigment, making the color more intense 

 than in the female. 



It will now be necessary to anticipate two of the laws 

 of heredity as quoted in Zoe from Haeckel.* "A third 

 law of conservative transmission may be called the law 

 of sexual transmission, according to which each sex 

 transmits to the descendants of the same sex peculiari- 

 ties which are not inherited by the descendants of the 

 other sex. * * * ^ fourth law of transmission, 

 which has here to be mentioned, in a certain sense con- 

 tradicts the last, and limits it, viz.: the law of mixed or 

 mutual (amphigonous) transmission. This law tells us 

 that every organic individual produced in a sexual way 

 receives qualities from both parents, from the father as 

 well as from the mother." 



Now, according to this law of mutual transmission, 

 there would be a constant tendency for the characters of 

 the male and female to combine more or less in the off- 

 spring. This tendency, if acting alone, would result in 

 an average color for both sexes. The females would be- 

 come darker and the males lighter. The katabolism of 

 the males, however, would tend to keep them at an 

 average distance in advance of the anabolic females, 

 and a tolerably constant ratio would be established. If, 

 then, there were nothing to hinder the female from ap- 

 proaching the characters of the male, the latter would 



* History of Creation, 1, pp. 209-210. 



