BIRD SONG HAWKINS. 465 



and even the development of weapons can not be satisfactorily explained by 

 sexual selection alone, for this is merely a secondary factor. In origin and 

 continued development they are outcrops of a male as opposed to a female con- 

 stitution. To sum \ip the position in a paradox, all secondary sexual charac- 

 ters are at bottom primary and are expressions of the same general habit of 

 body (or to use the medical term, diathesis), as that which results in the pro- 

 duction of male elements in the one case, or female elements in the other. 



This essential difference between the two sexes which expresses 

 itself in differences of plumage and song is further emphasized by 

 the facts, first, that many of the secondary sexual characters ap- 

 pear only at sexual maturity. Thus some of the male birds are dull 

 colored when young like the female and acquire the brighter colors 

 only on full development. Again, when the sex organs are removed 

 by castration, the male ornaments or weapons of battle disappear. 

 In cattle castration reduces the size of the horns, and after castra- 

 tion of the stag he never renews his antlers. 



In the case of young cocks the effects of castration are very vari- 

 able, sometimes increasing, sometimes decreasing the secondary sex 

 characters. One result is clear, however, that the whole body is 

 affected ; the larynx is intermediate in size between that of cock and 

 hen, the syrinx is weakly developed and the capons seldom crow or 

 do so abnormally, the brain and heart are lighter in weight, fat ac- 

 cumulates in the subcutaneous and subserous connective tissues, and 

 the skeleton shows many abnormalities. 



The conclusion seems inevitable that neither Darwin nor Wallace 

 reached the root of this matter. "The males are stronger, hand- 

 somer, or more emotional, simply because they are males; i. e., of 

 more active physiological habit than their mates." This view does 

 not wholly eliminate either natural or sexual selection. These may 

 be limiting, and, in a sense, directive factors, but it is fundamentally 

 the nature of sex which determines the gay color or the vigorous song. 



To complete our review of this controversy which has been waged 

 between ornithologists, we must record some of the more recent dis- 

 cussions of the Darwinian theory of sexual selection. Hudson says : 



The result of such independent investigation will be a conviction that con- 

 scious sexual selection on the part of the female is not the cause of music and 

 dancing performances in birds, nor of the brighter colors and ornaments that 

 distinguish the male. It is true that the female of some species, both in the 

 vertebrate and insect kingdoms, do exercise a preference ; but in a vast majority 

 of species the male takes the female he finds, or that he is able to win from 

 other competitors; and if we go to the reptile class we find that in the ophidian 

 order, which excels in variety and richness of color, there is no such thing as 

 preferential mating; and if we go to the insect class, we find that in butterflies, 

 which surpass all other creatures in their glorious beauty, the female gives her- 

 self up to the embrace of the first male that appears, or else is captured by the 

 strongest male, just as she might be by a mantis or some other rapacious insect. 



