becomes very manifest, and hence our dwindling native populations, if we take that word to mean the families that have been in the country for more than two generations. Nature does not confide conditions in humanity entirely to man, however. This would be to leave mankind subject to certain whims and fashions and the caprices of times and people. There are many biological checks which maintain mankind in a certain equilibrium. A typical example of it is the regulation of the number of each sex born. In general the proportion of the sexes to one another maintains a ratio very near that of equality under ordinary natural conditions. This obtains in spite of the fact that man is so much more subject to accidents than woman, so much more likely to catch and succumb to disease and so much more likely to wear himself out prematurely as the result of his labors. The death-rate among women at all ages is lower than that of men, yet a constant, definite equilibrium of the sexes is maintained with accurate nicety. There is evidently some check existing in nature itself that prevents any disturbance of this fixed ratio. Not only is nature able to maintain this, but in cases where, because of some serious disturbance of natural conditions, a decided inequality of the ratio occurs by accident, nature is able to restore conditions to the previous normal, without our being quite able to understand just how this is {260} accomplished. We do not know how sex is determined. There have been many explanations offered, but all of them have proved inadequate and most of them quite nugatory. In spite of our lack of knowledge there have been times in history when a striking manifestation of nature's power has occurred. For instance, after the Thirty Years' War in Germany the ratio between the sexes had been so much disturbed that, according to some historians, there were probably nearly twice as many women as men in existence in the Germanic countries. The men had been cut off by the war itself, by famines consequent upon it, by extreme and unusual efforts to support their families and by epidemic diseases in camps and campaigns. The disproportion was so great that a relaxation of the marriage laws was permitted for a time in certain of the countries and men were allowed to have two wives. Under these conditions nature at once began to reassert herself, the number of male births was greatly increased and the disproportion between the sexes immediately began to lessen. At the end of scarcely more than three generations the normal equilibrium of the sexes was restored and there was about an equal number of men and women again. Here we have the effect of one of these curiously interesting biological checks upon man's foolish quarrelsomeness which might result in a too great disproportion of the sexes.