We may also add that a protracted domicile, together with the habits of life contracted on very high or cold regions, may have for a further result that polyandry lays no excessive demands upon a woman. The women themselves are correspondingly affected in their nature. That they are so is rendered probable by the circumstance that, among the Eskimo girls, menstruation sets in only with the nineteenth year, whereas in the warm zones it sets in as early as the tenth or eleventh, and in the temperate latitudes between the fourteenth and the sixteenth year. In view of the fact that warm climates, as universally recognized, exercise a strongly stimulating influence upon the sexual instinct,--whence polygamy finds its widest diffusion in warm countries--it is quite likely that cold regions--to which high mountains and plateaus belong, and where the thinner air may also contribute its share--may exercise materially a restringent effect upon the sexual instinct. It must, moreover, be noted that experience shows conception occurs rarer with women who cohabit with several men. The increase of population is, accordingly, slight under polyandry; and it fits in with the difficulty of securing subsistence, encountered in cold lands and mountain regions;--whereby additional proof is furnished that also, in this, to us so seemingly strange phenomenon of polyandry, production has its determining influence upon the relations of the sexes. Finally, it is to be ascertained whether among these peoples, who live on high mountains or in cold zones, the killing of girl babies is not a frequent practice, as is oft reported of the Mongolian tribes, on the highlands of China. Exactly the reverse of the custom among the Romans during the Empire, of allowing celibacy and childlessness to gain the upper hand, was the custom prevalent among the Jews. True enough, the Jewish woman had no right to choose; her father fixed upon the husband she was to wed; but marriage was a duty, that they religiously followed. The Talmud advises: "When your daughter is of marriageable age, give his freedom to one of your slaves and engage her to him." In the same sense the Jews followed strictly the command of their God: "Increase and multiply." Due to this, and despite all persecutions and oppression, they have diligently increased their numbers. The Jew is the sworn enemy of Malthusianism.