Part 62

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 │ NUMBER OF FOALS BORN. │ Sexual ratio. SERVED. │ │ ─────────────────┼─────────────────┬─────────────────┼───────────────── „ │ 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 │ 24│ 124│ 19.4 Scherif │ │ │ Palestine: │ │ │ Rehoboam, King │ 28│ 60│ 46.6 of the Jews │ │ │ Arabia: Imon of │ 14│ 74│ 18.9 Sana │ │ │ Turkey: nine │ 110│ 128│ 85.9 sultans │ │ │ ═════════════════╧═════════════════╧═════════════════╧═════════════════

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.

Düsing, starting from the common belief that all animals have the faculty, when there is a lack of individuals of one sex, of procreating an excess of offspring of the sex which is deficient and thus of restoring the balance between the sexes, maintains that numerous factors, through the co-operation of which the sexual ratio is regulated, act in temporal succession. He shows that the individuality of the mother has an influence upon the sex. But this finds expression through the qualitative constitution of the ovum; hence already before fertilization there must exist a tendency toward the development of one sex or the other—for example, younger ova tend to become females; older ova, on the contrary, to become males. It has further been shown that the individuality of the father, that is to say, the qualitative constitution of the sperm, has an influence in the determination of sex. Thus, by means of the influence of the sperm, the already-mentioned pre-existing tendency of the ovum can in some instances be counteracted and overpowered. The influences in the personality of the father and of the mother, which during fertilization find expression in the qualitative constitution of the sperm and of the ovum, respectively, can thus bring about a resultant tendency, acting in one direction or the other with varying force. Thus, after fertilization, we have this resultant tendency toward the formation of a male or female embryo.

But, Düsing continues, at this time the sex is not definitely determined. The influence of the nutritive condition in which the fertilized ovum finds itself has yet to make itself felt. This influence on the determination of sex through the maternal nutrition, continues (in the human embryo) for as long as three months, but even when the reproductive organs of the embryo have definitely begun to diverge in the direction of the masculine or the feminine type, as the case may be, some nutritive influence, if it is sufficiently powerful, may yet turn the balance in the other direction, so that a partial or complete hermaphrodite results, a being uniting the characteristics of both sexes.

Actual inheritance of sex, of which people used to speak, cannot, in Düsing’s opinion, possibly occur. The mode in which one sex or the other develops is indeed inherited; but the decision which sex shall develop does not depend upon inheritance, but is determined by the co-operation of several outward influences. The qualities by which this is effected are acquired by adaptation to general or special vital conditions.

Wilckens (“A study of the Sexual Ratio and of the Causes of the Determination of Sex in Domestic Animals”) opposes the views of Düsing, on account of the results of his own investigations, relating to the births of 30,000 domestic animals. He formed the following conclusions:

1. Locality (soil and climate) has an influence upon the sexual ratio and upon the determination of sex in domestic animals, but this influence is probably indirect only, being exerted through the intermediation of the nutrition of the embryo in utero.

2. The season in which the domestic animal is conceived affects the sex; the hot season favours the production of males, the cold season that of females; in the hot season, in general, the appetite and nutrition of domestic animals diminish, whereas in the cold season these increase.

3. Regarding the male progenitor, neither his age, nor his sexual energy, nor the demand made upon that energy, nor the age of the semen, has any influence upon the sexual ratio or the determination of the sex of the offspring.

4. The age of the female progenitor influences the sexual ratio and the determination of the sex of the offspring in this way, that in general, primiparæ and young mothers conceive a larger number of female offspring. This influence of age may be referred to the fact that in general young mothers nourish their offspring in utero better than older mothers.

5. The nutrition of the fruit in utero influences the determination of sex, speaking generally, in the following way, that better nutrition favours the determination of the female sex, worse nutrition favours the determination of the male sex.

6. In addition to the influence of nutrition of the fruit upon the determination of sex, other influences, whose nature still remains obscure, must also co-operate, because one and the same progenitor in similar nutritive conditions does not always procreate offspring of the same sex.

7. Owing to the operation of these unknown influences, prediction of the sex of the offspring, and voluntary determination of the sex of the offspring, remain impossible. All we can say is that there is some probability that young and well-nourished mothers will procreate a comparatively larger number of female offspring, whilst elderly and ill-nourished mothers will procreate a comparatively larger number of male offspring.

II. Anatomical Investigations.

Of anatomical investigations and discoveries, those more especially relating to the sex-relationships of twins and triplets have been applied to the elucidation of the problem of the determination of sex.

The first and most important fact in this connection, one that is not merely a rule confirmed again and again by anatomists and gynecologists, but is further, as Mayrhofer has demonstrated as a result of his researches in von Braun’s clinic, a “natural law,” is this, that twins and triplets enclosed in a common chorion are invariably of the same sex. The sex-identity of such twins has been referred to the similarity of their nutritive conditions (Leuckart, Ploss), and more especially to the communication between their bloodvessels; and an intimate connection between these relationships and the determination of sex has been believed to exist.

Mayrhofer, however, opposes this assumption by the following deductions (“The Determination of Sex in the Human Species”); “Fœtuses enclosed within a single chorion always possess a common placenta, in which the blood-channels from both umbilical cords frequently, in the case of twins perhaps invariably, communicate. It might therefore be supposed that the sex-identity of embryos enclosed within a single chorion is due to the intermixture of their blood in the placenta. Hyrtl, however, describes a triplet’s placenta, in which, though all three fœtuses were enclosed within a single chorion, the vessels passing to the umbilical cord of one of the fœtuses were entirely distinct from the vascular area common to the two other fœtuses; it is therefore probable that in the case also of twins enclosed within a single chorion there is not necessarily any communication between their bloodvessels in the common placenta. But even if it were proved that in the case of twins enclosed within a single chorion their bloodvessels always do communicate in the common placenta, we could not therefore infer that the intermixture of the blood of the two fœtuses is the cause of their sexual identity.

“For the intermixture of the blood of the two fœtuses in the common placenta could never lead to a complete identity in the composition of the blood of the two; it could only lead to a diminution of the differences which would exist between the bloods if their placental circulations were entirely distinct, and the similarity in the bloods thus established could not be expected to do more than make it a general rule that such twins or triplets should be of the same sex; but to this rule exceptions might be expected to occur in certain cases, as when hæmatopoiesis in the two (or three) fœtuses was very different, or when the circulation through the intercommunicating bloodvessels was interfered with through the pressure of fibrinous deposits—differences between the bloods would then arise sufficient to cause differences in sex (if identical composition of the bloods is presumed to be the cause of the sexual identity).

“Experience teaches us that the existence of communicating vessels in the placenta does not suffice to induce a close similarity of growth and of the formation of the organs in twin fœtuses; nor does it prevent the illness and death of one fœtus leaving the health of the other undisturbed, although the communicating channels remain open; so that, if we except acardiac monsters, it is correct to say that each fœtus pursues a secluded life, uninfluenced by the life of its neighbour. Acardiac monsters, on the other hand, always receive blood which has already served for the nutrition of the normal fœtus, and the result of this is an arrested development and a striking preponderance of connective tissue in the acardiac twin. But notwithstanding the fact that the failure of its own proper circulation (which is indeed rendered possible by the existence of the communicating vessels in the placenta) leads to its defective nutrition with a blood inferior to that supplied to the normal fœtus, the acardiac monster is always of the same sex as the normal twin.”

From these considerations Mayrhofer rightly infers that the identity of sex of two fœtuses contained in a single chorion, since it does not depend upon the existence of communicating vessels in the placenta, must arise from a developmental tendency already existing in the two germs at the time of conception—or, in other words, that at the time of conception their sex is already inalterably determined.