See, e.g., Parerga und Paralipomena, bd. I, p. 189, and bd. 2, p. 482. Moll has also discussed this point (Untersuchungen über die Libido Sexualis, bd. I, pp. 384 et seq.).
Speaking of some South American tribes, he remarks (Travels, English translations, 1814, vol. iii. p. 236) that they "have as great an antipathy to the beard as the Eastern nations hold it in reverence. This antipathy is derived from the same source as the predilection for flat foreheads, which is seen in so singular a manner in the statues of the Aztec heroes and divinities. Nations attach the idea of beauty to everything which particularly characterizes their own physical conformation, their natural physiognomy." See also Westermarck, History of Marriage, p. 261. Ripley (Races of Europe, pp. 49, 202) attaches much importance to the sexual selection founded on a tendency of this kind.
"Differences of race are irreducible," Abel Hermant remarks (Confession d'un Enfant d'Hier, p. 209), "and between two beings who love each other they cannot fail to produce exceptional and instructive reactions. In the first superficial ebullition of love, indeed, nothing notable may be manifested, but in a fairly short time the two lovers, innately hostile, in striving to approach each other strike against an invisible partition which separates them. Their sensibilities are divergent; everything in each shocks the other; even their anatomical conformation, even the language of their gestures; all is foreign."