Fraternal polyandry being declared superior to polyandry of the Naïr type, it has been concluded that in virtue of the law of progress it must have been preceded in all times and places by the latter. As regards the greater number of cases of Thibetan polyandry, the supposition is gratuitous; it seems, however, established as far as ancient Arabia is concerned, where, thanks to a very learned treatise recently published by Mr. W. Robertson Smith, professor of Arabic at the University of Cambridge,[196] we may note the causes of polyandry and follow its evolution. III. _Polyandry in Ancient Arabia._ The chief cause of ancient Arabian polyandry was the one we find in nearly all the polyandric countries--that is to say, the infanticide of daughters. The primitive Arabs, extremely savage and even anthropophagous, were led to adopt the custom of female infanticide by the difficulty of living in their arid country, where famines were very common. Down to the present time the nomads of Arabia suffer constantly from hunger during a great part of the year.[197] The custom of infanticide was inveterate among the Arabs, and Mahomet was obliged to condemn it over and over again in the Koran:--“They who from folly or ignorance kill their children shall perish.[198] Kill not your children on account of poverty.[199] Kill not your children for fear of poverty; we will feed them, and you also.[200] When it shall be asked of the girl buried alive for what crime she is put to death ... every soul will then acknowledge the work that she had done.”[201]