females prefer or are most excited by the more brilliant males” (p. 316).  Among birds also the males “endeavor to charm or excite their mates by love-notes,” etc., and “the females are excited by certain males, and thus unconsciously prefer them” (p. 367), while ornaments of all kinds “apparently serve to excite, attract, or fascinate the female” (p. 394).  In a supplemental note, also, written in 1876, five years after the first publication of the Descent of Man, and therefore a late statement of his views, Darwin remarks that “no supporter of the principle of sexual selection believes that the females select particular points of beauty in the males; they are merely excited or attracted in a greater degree by one male than by another, and this seems often to depend, especially with birds, on brilliant coloring” (p. 623).  Thus, on the one hand, Darwin interprets the phenomena as involving a real esthetic element, a taste for the beautiful; on the other hand, he states, without apparently any clear perception that the two views are quite distinct, that the colors and sounds and other characteristics of the male are not an appeal to any esthetic sense of the female, but an appeal to her sexual emotions, a stimulus to sexual excitement, an allurement to sexual contact.  According to the first theory, the female admires beauty, consciously or unconsciously, and selects the most beautiful partner[22]; according to the second theory, there is no esthetic question involved, but the female is unconsciously influenced by the most powerful or complex organic stimulus to which she is subjected.  There can be no question that it is the second, and not the first, of these two views which we are justified in accepting.  Darwin, it must be remembered, was not a psychologist, and he lived before the methods of comparative psychology had begun to be developed; had he written twenty years later we may be sure he would never have used so incautiously some of the vague and hazardous expressions I have quoted.  He certainly injured his theory of sexual selection by stating it in too anthropomorphic language, by insisting on “choice,” “preference,” “esthetic sense,” etc.  There is no need whatever to burden any statement of the actual facts by such terms borrowed from human psychology.  The female responds to the stimulation of the male at the right moment just as the tree responds to the stimulation of the warmest days in spring.  We should but obscure this fact by stating that the tree “chooses” the most beautiful days on which to put forth its young sprouts.  In explaining the correlation between responsive females and accomplished males the supposition of esthetic choice is equally unnecessary.  It is, however, interesting to observe that, though Darwin failed to see that the love-combats, pursuits, dances, and parades of the males served as a method of stimulating the impulse of contrectation—­or, as it would be better to term it, tumescence—­in the male himself,[23] he to some extent realized the part thus played in exciting the equally necessary activity of tumescence in the female.