It may well be, as Crawley argues (The Mystic Rose, Chapter XVII), that sexual taboo plays some part among primitive people in preventing incestuous union, as, undoubtedly, training and moral ideas do among civilized peoples.
The remarks of the Marquis de Brisay, an authority on doves, as communicated to Giard (L'Intermédiare des Biologistes, November 20, 1897), are of much interest on this point, since they correspond to what we find in the human species: "Two birds from the same nest rarely couple. Birds coming from the same nest behave as though they regarded coupling as prohibited, or, rather, they know each other too well, and seem to be ignorant of their difference in sex, remaining unaffected in their relations by the changes which make them adults." Westermarck (op. cit., p. 334) has some remarks on a somewhat similar tendency sometimes observed in dogs and horses.
See Appendix to vol. lii of these Studies, "The Sexual Impulse among Savages."
See, especially, ante, pp. 163 et seq.