In primitive human races we very frequently trace precisely the same influence of the seasonal impulse as may be witnessed in the higher animals, although among human races it does not always result that the children are born at the time of the greatest plenty, and on account of the development of human skill such a result is not necessary. Thus Dr. Cook found among the Eskimo that during the long winter nights the secretions are diminished, muscular power is weak, and the passions are depressed. Soon after the sun appears a kind of rut affects the young population. They tremble with the intensity of sexual passion, and for several weeks much of the time is taken up with courtship and love. Hence, the majority of the children are born nine months later, when the four months of perpetual night are beginning. A marked seasonal periodicity of this kind is not confined to the Arctic regions. We may also find it in the tropics. In Cambodia, Mondière has found that twice a year, in April and September, men seem to experience a "veritable rut," and will sometimes even kill women who resist them.[129] These two periods, spring and autumn--the season for greeting the appearance of life and the season for reveling in its final fruition--seem to be everywhere throughout the world the most usual seasons for erotic festivals. In classical Greece and Rome, in India, among the Indians of North and South America, spring is the most usual season, while in Africa the yam harvest of autumn is the season chiefly selected. There are, of course, numerous exceptions to this rule, and it is common to find both seasons observed. Taking, indeed, a broad view of festivals throughout the world, we may say that there are four seasons when they are held: the winter solstice, when the days begin to lengthen and primitive man rejoices in the lengthening and seeks to assist it;[130] the vernal equinox, the period of germination and the return of life; the summer solstice, when the sun reaches its height; and autumn, the period of fruition, of thankfulness, and of repose. But it is rarely that we find a people seriously celebrating more than two of these festival seasons.