EVOLUTION OF THE COLORS OF BIRDS. 81 



a struggle for existence in relation to other organic 

 beings or to external conditions, but on a struggle be- 

 tween the individuals of one sex, generally the males, 

 for the possession of the other sex. The result is not 

 death to the unsuccessful competitor, but few or no 

 offspring." There are two forms of sexual selection, the 

 law of battle which is universally admitted, and " pref- 

 erential mating " as Lloyd Morgan has termed it,* which 

 is doubted by many. It is known that the males of many 

 animals, especially among mammals and birds, fight 

 among themselves for a female, the victor carrying off 

 the prize. There can be little doubt that.in such cases the 

 i inore powerful males become the parents of the race, and 

 that every advantage which they may possess in the way 

 of strength, agility, or special weapons, such as antlers 

 or spurs, will be selected in accordance with the law of 

 battle. Preferential mating is thus described by Darwin :f 

 " Amongst birds, the contest is often of a more peaceful 

 character. All those who have attended to the subject, 

 believe that there is the severest rivalry between the 

 males of many species to attract, by singing, the females. 

 The rock-thrush of Guiana, birds of paradise, and some 

 others, congregate; and successive males display with 

 the most elaborate care, and show off in the best manner 

 their gorgeous plumage; they likewise perform strange 

 antics before the females, which, standing by as specta- 

 tors, at last choose the most attractive partner. Those 

 who have closely attended to birds in confinement well 

 know that they often take individual preferences and 

 dislikes. Thus Sir R. Heron has described how a pied 

 peacock was eminently attractive to all his hen birds. I 

 cannot here enter on the necessary details, but if man 

 can in a short time give beauty and an elegant carriage 



* Animal Life and Intelligence, p. 198. 

 t 1. c., p. 109. 

 G 



