Baust gives a report, based, he says, upon “thoroughly trustworthy data,” furnished by personal friends, regarding 14 cases, which show, in his opinion, that every conception occurring in a week after the cessation of the menstrual flow leads to the birth of a girl; but that when conception occurs on the fifth or sixth day after menstruation the result varies as regard sex. Swift, from a report of 20 cases, draws the conclusion that in the intermenstrual interval, boys, in the latter part of the interval girls are conceived.
The influence of the strength of menstruation upon the determination of sex has also been studied by the statistical method, starting with the idea that menstruation, in proportion to its strength, affords on the average a measure for the subsequent nutrition of the embryo, and this nutrition is further supposed to determine the sex. Düsing therefore arranged the births occurring in the lying-in hospitals of Dresden, Leipzig and Jena, according to the information given regarding menstruation in the clinical history of each case; it appeared that when menstruation was comparatively scanty, there was a greater excess of boys than when menstruation was comparatively abundant. The actual figures were the following:
| Abundant menstruation. | Scanty menstruation. | |||
|---|---|---|---|---|
| Dresden | 902 | 847 | 495 | 431 |
| Jena | 66 | 69 | 56 | 45 |
| Leipzig | 21 | 22 | 239 | 211 |
| Totals | 989 | 938 | 790 | 687 |
| Sexual ratio | 105.4 | 114.7 | ||
Here also we may append the figures obtained by Düsing regarding the births of foals at the Prussian stud-farms, which he regards as supporting his view that by natural selection all animals have acquired the faculty, whenever stronger demands are made upon their sexual capacity, of procreating a larger number of individuals of their own sex. In the tables we learn how many mares on an average a stallion had covered in each year, that is, we learn how great were the demands made upon the sexual capacity of the stallion in that particular breeding stable in that year. The figures relating to the years 1859 to 1892 were tabulated and averages were drawn with the following results:
| Number of Mares Served. | Number of Foals Born. | Sexual ratio. | |
|---|---|---|---|
| Colts. | Fillies. | ||
| 60–70 | 42,445 | 41,933 | 101.22 |
| 55–59 | 56,511 | 66,226 | 100.49 |
| 50–54 | 59,940 | 61,096 | 98.18 |
| 45–49 | 57,077 | 59,216 | 96.39 |
| 40–44 | 59,967 | 62,007 | 96.71 |
| 35–39 | 38,348 | 40,181 | 95.44 |
| 20–34 | 26,354 | 27,069 | 97.35 |
From these figures, which relate a very large number of instances indeed, we learn that when greater demands are made upon the stallion, more males are procreated. In fact, except for two slight divergencies, the rise in the sexual ratio proceeds strictly pari passu with the increase in the number of mares covered.
I must, however, draw attention to the fact that this assumption when applied to the human species, that the man on whom whose sexual capacity especially extensive demands are made, procreates an especially large number of male children, is not confirmed by the sexual ratio among the offspring of polygamous marriages in which unquestionably greater demands are made upon the husband’s sexual powers than is the case in monogamic unions.
The reports of travellers of earlier days, to the effect that in Oriental countries more girls are born than boys, have recently been confirmed by several observers. Campbell states that in the harems of Siam the number of boys and girls born is equal. Clarke states that among the Mohammedan Indians more girls are born than boys. According to McLennan Indian experience teaches us that where polyandry prevails male offspring predominate in numbers; but where polygamy prevails there is, on the contrary, an excess of female infants. The following data collected by Goehlert from historical reports and from genealogical writings, regarding the progeny of notable persons living in polygamous unions, show certainly a large excess of female offspring over male:
| Children. | Sexual ratio. | ||
|---|---|---|---|
| Male. | Female. | ||
| Morocco: Muley Scherif | 24 | 124 | 19.4 |
| Palestine: Rehoboam, King of the Jews | 28 | 60 | 46.6 |
| Arabia: Imon of Sana | 14 | 74 | 18.9 |
| Turkey: nine sultans | 110 | 128 | 85.9 |
According to Tousenel, love marriages give rise to more daughters than sons, whereas among the offspring of conventional or compulsory marriages, male children predominate. Further, among the offspring of legitimate unions, the excess of males is greater than among the offspring of illegitimate unions. A physician, V. J. Cook, maintains that boys are procreated in the evenings (before midnight), but girls during the early morning hours—at which latter time women are less “impressionable” than during the evening hours.