INTRODUCTION " 29 



sufficient evidence, whereas, after careful consideration, I can 

 find no evidence of any necessary or general connection 

 between health and vigour, or anatomical features, and the 

 special peculiarities in which one sex differs from the other. 



Other suggestions or theories which have been propounded 

 in explanation of the evolution of secondary sexual characters 

 appear to be merely ingenious variations of the idea of selec- 

 tion. Stolzmann 1 has maintained that among birds the males 

 are more numerous than the females, which of course is one 

 of the main points in Darwin's theory. According to Stolz- 

 mann the fact is a necessary consequence of the defective 

 or scanty nourishment of the eggs. The female devoting her 

 energies and labour to the work of nest-building takes less 

 food and performs more work than she otherwise would, and 

 consequently the nutrition of the eggs is less generous, 

 Scantily-nourished eggs produce males rather than females, 

 and the majority of birds' eggs being scantily nourished, 

 males are in a majority among the young produced. It is 

 obvious that this argument does not deserve serious attention. 

 It is certain that birds' eggs, as compared for instance with 

 those of fishes, amphibia, or mammals, are supplied with an 

 enormous quantity of the most nutritious food-yolk, and it is 

 difficult under these circumstances to understand what is 

 meant by the assertion that they are badly nourished. 



However, to continue Stolzmann' s argument, the excess 

 of male birds is pernicious to the species, not only on account 

 of their interference with the females during the performance 

 of their maternal duties, but also because they occupy 

 valuable space and lessen the supplies of food. Anything 

 therefore tending to lessen the undue excess of males would 

 be seized upon and perpetuated by natural selection. Hence 

 the gaudy colours, crests and spurs, and pugnacious habits 

 of the males. The bright colours render them visible not 



1 Proc. Zool. Soc. 1885. 



