Wallace's Theory 



the powers of defence and concealment possessed 

 by the species." 



In support of his contention, Wallace asserts 

 that all species of birds, of which the hens are as 

 conspicuously coloured as the cocks, nest in holes 

 or build domed nests. The plumes and other 

 ornaments, which the cocks of certain species 

 display, Wallace would attribute to a surplus of 

 strength, vitality, and growth power, which is 

 able to expend itself in this way without injury. 



"If," he writes, "we have found a vera causa 

 for the origin of ornamental appendages of birds 

 and other animals in a surplus of vital energy, 

 leading to abnormal growths in those parts of 

 the integument where muscular and nervous 

 action are greatest, the continuous development 

 of these appendages will result from the ordinary 

 action of natural selection in preserving the most 

 healthy and vigorous individuals, and the still 

 further selective agency of sexual struggle in 

 giving to the very strongest and most energetic 

 the parentage of the next generation." (Dar- 

 winism, p. 293.) "Why," he says, "in allied 

 species the development of accessory plumes 

 has taken different forms we are unable to say, 

 except that it may be due to that individual 

 variability which has served as the starting point 

 for so much of what seems to us strange in form, 

 or fantastic in colour, both in the animal and 

 vegetable world." 



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