of unsterilized water. But here, too, in modern warfare, this item is becoming less selective, with the advance in discipline and in organized sanitation.
The efficiency of selection will be affected by the percentage that each side has sent to the front, if the combatants are either above or below the average of the population. A nation that sends all its able-bodied males forward will be affected differently from its enemy that has needed to call upon only one-half of its able-bodied men in order to win its cause.
Away from the fighting lines of the contending sides, conditions that prevail are rendered more severe in many ways than in times of peace. Poverty becomes rife, and sanitation and medical treatment are commonly sacrificed under the strain. During a war, that mitigation of the action of natural selection which is so common now among civilized nations, is somewhat less effective than in times of peace. The scourge of typhus in Serbia is a recent and graphic illustration.
After a war has been concluded, certain new agencies of inter-group selection arise. The result depends largely on whether the vanquished have had a superior culture brought to them, as in the case of the Philippines, or whether, on the contrary, certain diseases have been introduced, as to the natives of the New World by the Spanish conquerors and explorers, or crushing tribute has been levied, or grievous oppression such as has befallen Belgium.
Sometimes the conquerors themselves have suffered severely as the result of excessive spoliation, which has produced vicious idleness and luxurious indulgence, with the ultimate effect of diminishing the birth-rate.
Within the nation there may be various results. Sometimes, by the reduction of overcrowding, natural selection will be less severe. On the other hand, the loss of that part of the population which