Archiv fuer Rassen und Gesellschafts-Biologie, Bd.  III, Heft 5) has also argued in favor of a chief sexual period in the year in man, with secondary and even tertiary climaxes, in March, August, and December.  He finds that in some families, for several generations, birthdays tend to fall in the same months, but his paper is, on the whole, inconclusive.

Some years ago, Prof.  J.B.  Haycraft argued, on the basis of data furnished by Scotland, that the conception-rate corresponds to the temperature-curve (Haycraft, “Physiological Results of Temperature Variation,” Transactions of the Royal Society of Edinburgh, vol. xxix, 1880).  “Temperature,” he concluded, “is the main factor regulating the variations in the number of conceptions which occur during the year.  It increases their number with its elevation, and this on an average of 0.5 per cent, for an elevation of 1 deg.  F.”  Whether or not this theory may fit the facts as regards Scotland, it is certainly altogether untenable when we take a broader view of the phenomena.

Recently Dr. Paul Gaedeken of Copenhagen has argued in a detailed statistical study ("La Reaction de l’Organisme sous l’Influence Physico-Chimiques des Agents Meteorologiques,” Archives d’Anthropologie Criminelle, Feb., 1909) that the conception-rate, as well as the periodicity of suicide and allied phenomena, is due to the action of the chemical rays on the unpigmented skin in early spring, this action being physiologically similar to that of alcohol.  He seeks thus to account for the marked and early occurrence of such periodic phenomena in Greenland and other northern countries where there is much chemical action (owing to the clear air) in early spring, but little heat.  This explanation would not cover an autumnal climax, the existence of which Gaedeken denies.

In order to obtain a fairly typical conception-curve for Europe, and to allow the variations of local habit and custom to some extent to annihilate each other, I have summated the figures given by Mayr for about a quarter of a million births in Germany, France, and Italy,[156] obtaining a curve (Chart 2) of the conception-rate which may be said roughly to be that of Europe generally.  If we begin at September as the lowest point, we find an autumn rise culminating in the lesser maximum of Christmas, followed by a minor depression in January and February.  Then comes the great spring rise, culminating in May, and followed after June by a rapid descent to the minimum.

In Canada (see e.g., Report of the Registrar General of the Province of Ontario for 1904), the maximum and minimum of conceptions alike fall later than in Europe; the months of maximum conception are June, July, and August; of minimum conception, January, February, and March.  June is the favorite month for marriage.

It would be of some interest to know the conception-curve for the well-to-do classes,