The Swedish physician Wargentin was the first to point out in 1767 this frequency in his own country. Since then, several statisticians, doctors, and naturalists have confirmed it: Quetelet for Belgium and Holland (maximum of births in February, the maximum of conceptions in May); Wappæus for Central Europe (two maxima of conception, in winter, and at the end of spring or the beginning of summer); Villermé (same periods) for different countries, including those of the southern hemisphere; Sormani for Italy (conceptions in July); Mayr for Germany (conceptions in December); Beukemann for the different provinces of the German empire (maximum of conceptions in December in the north, in spring in the south); Hill for India (maximum of conceptions, December-January); lastly, different authors for Russia (maximum of conceptions in winter).
The explanations which have been put forward up to the present of this phenomenon are of different kinds. According to certain authors, the maxima observed in many countries in the spring are owing to the fact of there being in this season “plenty of everything,” better nourishment, in short, something which compels the genesic instinct of man, like that of most animals, to participate in the “awakening of nature.” To this it is replied by other observers that in certain countries the maxima are reported in the winter months, that is to say in the season when the temperature and the relative absence of the good things of life do not seem to be a priori favourable to generation; these scientists look for the cause in the social organisation. They notice that in countries of the north it is in the month of December that, after having finished their work in the fields, the inhabitants give themselves up to festivities and rejoicings, and that it is in this month the greatest number of unions are contracted; on the other hand, in the south the most popular festivals are those of the spring at the awakening of nature. Others, again, assert that these differences are owing as much to religion as to latitude.
All these explanations are somewhat unscientific, and have never been verified by figures or experience. According to Rosenstadt,[129] cosmic and social influences do not count at all in the question, for often the periods during which recrudescence of conceptions occurs are the same for countries differing entirely in climate, religion, and manners (Italy, Russia, Sweden). These influences may, at the most, create conditions favourable to the bringing about of the phenomenon, may prepare the ground for it. But as to the phenomenon itself it would be, according to Rosenstadt, merely the remains in man of his animal nature, a “physiological custom” inherited from the animals, his ancestors.
Primitive man would inherit from his ancestors the habit of procreating by preference at particular times. On the arrival of this period of sexual excitement fecundations would take place wholesale. With the development of civilisation man has sexual relations all the year round, but the “physiological custom” of procreating at a certain period does not entirely disappear; it remains as a survival of the animal state, and manifests itself in the recrudescence of the number of conceptions during certain months of the year. This conclusion is corroborated by the fact that among certain savage tribes copulation seems to take place at certain periods of the year; for example, among the Australians at the time of the yam harvest (see [Chap. VII.], Marriage, etc.).[130]
It is perhaps as a survival of these habits that we must regard the annual festivals followed by wholesale marriages among the Sonthals, and the wholesale marriages still practised to-day in Brittany on the eve of Lent. Thus in the little market-town of Plougastel-Daoulas (Finistère), containing only 7000 inhabitants, thirty-four marriages were celebrated at once on the 5th of February 1896, and the preceding year, before Lent, forty-eight couples had been united on the same day in this locality.[131] The famous “Bharzwad Jang,” or “Marriage of the Shepherds,” a ceremony practised by certain tribes (Mer, Shir, Rabai) of Western Kathiawar (India), is also perhaps a survival of this custom. It consists in the celebration of marriage on the same day, but at stated intervals (of about twenty-four years), of all the bachelors of the tribe. At the last ceremony of this kind, which took place from the 28th of April to the 3rd of May 1895, 775 couples were thus married at once.[132]
The question of the fertility of women in different populations is one of great interest as regards the future of these populations, but it is scarcely more than outlined yet. If we know in a general way that the birth-rate is very low in France and somewhat low in the non-immigrant part of the population of the United States, that it is very high in Russia and among the Jews, etc., we know almost nothing about the subject in connection with uncivilised peoples; in their case, as in our own, we must take into account the different elements of the problem—social conditions, voluntary limitation (Australians), infanticide (Polynesia), etc.
Influence of Environment.—I can scarcely treat here as fully as I could wish such interesting questions as the influence of external circumstance, of acclimatation and crossings or hybridisation, inasmuch as they are still very little and imperfectly studied. The direct influence of environment has rarely been observed with all the scientific exactness to be wished. Ordinarily we have to rest satisfied with phrases which do not mean a great deal.[133] Even the influence of conditions so abnormal as the complete absence of light and solar heat, those sources of everything living, during several months, has only been observed incidentally. Nossiloff,[134] however, has noted day by day the influence of the polar night on an ordinary population (not hardened and picked, like the crews of polar expeditions) and proved its depressing action, manifesting itself in general apathy of body and mind, in a tendency to drowsiness, and in diminution of the height and the thoracic perimeter; this action is especially noticeable in children, who visibly pine away during this period. Unfortunately the observations of Nossiloff are limited to a small number of subjects.
It is more than probable that all the modifications which the organism undergoes as a result of the influence of environment are mostly of a chemical nature, and have only a remote effect on the human frame. According to W. Kochs,[135] the whole question of acclimatation in tropical countries resolves itself into the quantity of water in the organism. He bases his deductions principally on the difference found to exist in the quantity of water contained in the flesh of oxen of the Argentine Republic in comparison with that found among cattle of Northern Germany. The former have from 80 to 83 per cent. of water, while the latter have from 72 to 75 per cent. only. If it is the same with man, as Kochs supposes, he would have from 7 to 8 per cent. less solid matter to burn in his body in the tropics than in temperate countries, and the vital energy would be affected accordingly. Thus only the organism that had acquired the quantity of water necessary for supporting the heat of the tropics would be acclimatised; this is so true that Whites acclimatised in tropical countries suffer more from the cold in Europe than their compatriots who have never left Europe.[136] Besides, the Negroes of Senegal begin to suffer from cold when the thermometer falls below 20° C. (68° Fahr.), whilst the Fuegians who are not more warmly clad bear very well the cold of 0° to -4° C. (32° to 25° Fahr.).
Taken as a whole, the genus Homo is cosmopolitan. In fact, man inhabits the whole earth from the icy regions of Greenland (in the neighbourhood of the eightieth degree of N. latitude) to the torrid zone which stretches between the tropic of Cancer and the Equator. He is found in countries situated at 75 or 200 metres below the level of the sea (Caspian depression, depression of Louktchin in Eastern Turkestan), as well as on table-lands at an elevation of more than 5000 metres (Thibet). But if we consider the numerous sub-divisions of the genus Homo which are called species, sub-species, or races, the question of cosmopolitanism becomes more complicated as at the same time the positive data for its solution are less numerous.
Apart from the European and Negro races, peoples have never changed their habitat abruptly—have not transported themselves in a body into climates very different from their native country, though slow migrations, advancing from place to neighbouring place, have been numerous at all times and among all peoples; these have been followed by acclimatation, the sole criterion of cosmopolitanism. It must also be remarked that civilised peoples withstand better than savages changes of every kind. In this respect the former bear a stronger resemblance than the latter to domestic animals, which rarely become sterile outside of their native country. According to Darwin,[137] this results from the fact that civilised peoples, as well as domestic animals, have been subjected in the course of their evolution to more numerous variations, more frequent changes of place, and also more important crossings.