Kulischer, studying the sexual customs of various human races, concluded that in primitive times, only at two special seasons—­at spring and in harvest-time—­did pairing take place; and that, when pairing ceased to be strictly confined to these periods, its symbolical representation was still so confined, even among the civilized nations of Europe.  He further argued that the physiological impulse was only felt at these periods.  (Kulischer, “Die geschlechtliche Zuchtwahl bei den Menschen in der Urzeit,” Zeitschrift fuer Ethnologie, 1876, pp. 152 and 157.) Cohnstein ("Ueber Praedilectionszeiten bei Schwangerschaft,” Archiv fuer Gynaekologie, 1879) also suggested that women sometimes only conceive at certain periods of the year.

Wiltshire, who made various interesting observations regarding the physiology of menstruation, wrote:  “Many years ago, I concluded that every women had a law peculiar to herself, which governed the times of her bringing forth (and conceiving); that she was more prone to bring forth at certain epochs than at others; and subsequent researches have established the accuracy of the forecast.”  He further stated his belief in a “primordial seasonal aptitude for procreation, the impress of which still remains, and, to some extent, governs the breeding-times of humanity.” (A.  Wiltshire, “Lectures on the Comparative Physiology of Menstruation,” British Medical Journal, March, 1883, pp. 502, etc.)

Westermarck, in a chapter of his History of Human Marriage, dealing with the question of “A Human Pairing Season in Primitive Times,” brings forward evidence showing that spring, or, rather, early summer, is the time for increase of the sexual instinct, and argues that this is a survival of an ancient pairing season; spring, he points out, is a season of want, rather than abundance, for a frugivorous species, but when men took to herbs, roots, and animal food, spring became a time of abundance, and suitable for the birth of children.  He thus considers that in man, as in lower animals, the times of conception are governed by the times most suitable for birth.

Rosenstadt, as we shall see later, also believes that men to-day have inherited a physiological custom of procreating at a certain epoch, and he thus accounts for the seasonal changes in the birthrate.

Heape, who also believes that “at one period of its existence the human species had a special breeding season,” follows Wiltshire in suggesting that “there is some reason to believe that the human female is not always in a condition to breed.” (W.  Heape, “Menstruation and Ovulation of Macacus rhesus,” Philosophical Transactions, 1897; id.  “The Sexual Season of Mammals,” Quarterly Journal Microscopical Science, 1900.)

Except, however, in one important respect, with which