It is important also to notice that, in regard to animals, the mode of sexual association may vary without much difficulty. No species is of necessity and always restricted to such or such a form of sexual union. An animal belonging to a species habitually monogamous may very easily become polygamous. In short, there does not seem to be any relation between the degree of intelligence in a species and its conjugal customs. In the following chapters it will be seen that, in great measure, these observations do not apply exclusively to animals. FOOTNOTES: [29] Espinas, _Soc. Animales_, pp. 343, 344. [30] _Ibid._ pp. 344, 345. [31] Espinas, _Soc. Animales_, pp. 336-396. [32] Darwin, _Descent of Man_, p. 375. [33] Lortet, _Comptes rendus de l’Académie des Sciences_, 1878. [34] Darwin, _Descent of Man_, p. 379. [35] _Ibid._ p. 244. [36] Espinas, _Soc. Animales_, p. 415. [37] _Ibid._ pp. 416, 417. [38] Houzeau, _Fac. mentales des animaux_, t. ii. p. 380. [39] _Dix-huit ans chez les sauvages_, etc., p. 374. [40] Espinas, _Soc. anim._, p. 427. [41] _Ibid._ p. 421. [42] Audubon, _loc. cit._, vol. i. p. 83. [43] _Ibid._ t. I^{er.} p. 292. [44] Darwin, _Descent of Man_, pp. 446, 449. [45] _Ibid._ p. 455. [46] Espinas, _Soc. Animales_, p. 422. [47] Audubon, _Scènes de la Nature_, t. I^{er.} p. 29. [48] Espinas, _loc. cit._ pp. 421-423. [49] Audubon, _loc. cit._ t. I^{er.} p. 209. [50] _Ibid._ t. ii. p. 13. [51] _Ibid._ [52] _Ibid._ t. I^{er.} p. 167. [53] _Ibid._ t. ii. p. 199. [54] _Ibid._ t. ii. p. 476. [55] _Ibid._ t. ii. p. 70. [56] _Ibid._ t. I^{er.} p. 347. [57] Audubon, _Scènes de la Nature_, t. I^{er.} p. 317. [58] Darwin, _Descent of Man_, p. 238. [59] Espinas, _Soc. Animales_, p. 448. [60] Darwin, _Descent of Man_, p. 238. [61] Darwin, _Descent of Man_, p. 443. [62] Espinas, _loc. cit._ p. 443. [63] Houzeau, _Facultés mentales des animaux_, t. ii. p. 394. [64] Darwin, _Descent of Man_, p. 238. [65] Espinas, _loc. cit._ p. 453. CHAPTER III. PROMISCUITY. I. _Has there been a Stage of Promiscuity?_--Promiscuity rare among the superior vertebrates--It has been exceptional in mankind. II. _Cases of Human Promiscuity._--Promiscuity among the Troglodytes, the ancient Arabs, the Agathyrses, the Anses, the Garamantes, the ancient Greeks, in the _Timæus_, in China, in India, among the Andamanites, in California, among the aborigines of India, among the Zaporogs, and the Ansarians--Insufficience of these proofs.