Part 60

══════════╤════════════╤════════════╤════════════╤════════════╤═══════════ Age of │ Leipzig. │ Dresden. │ Jena. │ Total Nos. │ Sexual primiparæ.│Boys. Girls.│Boys. Girls.│Boys. Girls.│Boys. Girls.│ ratio. ──────────┼────────────┼────────────┼────────────┼────────────┼─────────── 15 │ 1 : −│ 1 : 2│ 1 : −│ 3 : 2│} 549 : 494 │ │ │ │ │ = 111.1 16 │ 4 : 4│ 6 : 10│ 2 : 2│ 12 : 16│ „ 17 │ 23 : 13│ 20 : 15│ 9 : 7│ 52 : 35│ „ 18 │ 67 : 55│ 103 : 100│ 17 : 13│ 187 : 168│ „ 19 │ 110 : 103│ 152 : 141│ 33 : 29│ 295 : 273│ „ ──────────┼────────────┼────────────┼────────────┼────────────┼─────────── 20 │ 148 : 147│ 187 : 185│ 32 : 45│ 367 : 377│} 807 : 781 │ │ │ │ │ = 103.3 21 │ 157 : 145│ 241 : 201│ 42 : 57│ 440 : 404│ „ ──────────┼────────────┼────────────┼────────────┼────────────┼─────────── 22 │ 120 : 133│ 191 : 207│ 48 : 53│ 359 : 393│} 903 : 962 │ │ │ │ │ = 93.9 23 │ 106 : 108│ 168 : 149│ 51 : 51│ 325 : 308│ „ 24 │ 71 : 105│ 111 : 118│ 37 : 38│ 219 : 261│ „ ──────────┼────────────┼────────────┼────────────┼────────────┼─────────── 25 │ 79 : 57│ 73 : 72│ 35 : 27│ 187 : 156│} 531 : 469 │ │ │ │ │ = 113.2 26 │ 45 : 35│ 30 : 43│ 20 : 20│ 125 : 98│ „ 27 │ 31 : 35│ 52 : 55│ 10 : 12│ 93 : 102│ „ 28 │ 32 : 33│ 26 : 33│ 19 : 16│ 77 : 72│ „ 29 │ 19 : 10│ 26 : 18│ 4 : 13│ 49 : 41│ „ ──────────┼────────────┼────────────┼────────────┼────────────┼─────────── 30 │ 9 : 15│ 30 : 13│ 9 : 6│ 48 : 34│} 155 : 104 │ │ │ │ │ = 150.0 31 │ 3 : 8│ 15 : 11│ 3 : 3│ 21 : 22│ „ 32 │ 5 : 6│ 12 : 9│ 7 : 3│ 24 : 18│ „ 33 │ 2 : 2│ 5 : 5│ 5 : 2│ 12 : 9│ „ 34 │ 4 : −│ 8 : 5│ 2 : −│ 14 : 5│ „ 35 │ 2 : −│ 9 : 3│ 2 : 1│ 13 : 4│ „ 36 │ 1 : −│ 3 : 3│ 1 : 1│ 5 : 4│ „ 37 │ 4 : 1│ 4 : 3│ 1 : −│ 9 : 4│ „ 38 │ − : −│ − : 1│ 1 : −│ 1 : 1│ „ 39 │ − : −│ 4 : −│ 1 : −│ 5 : −│ „ 40 │ 1 : 1│ 2 : 1│ 1 : −│ 4 : 2│ „ 41 │ − : −│ − : 1│ − : −│ − : 1│ „ ──────────┴────────────┴────────────┴────────────┴────────────┴───────────

As an explanation of this statistically proved fact, that elderly primiparæ gave birth to a large excess of boys, Düsing suggests that these women who conceive for the first time comparatively late in life, are, prior to the conception, in a state corresponding with that of a lower animal species suffering from a deficiency of males, and for this reason exhibit a tendency to procreate a larger number of individuals of the deficient sex. In multiparæ also it is possible to trace the influence of a deficiency of male individuals. When there is such a deficiency the interval between successive births is unduly protracted. Düsing found (once more from the records of the lying-in hospitals of Dresden, Leipzig and Jena) that the longer the interval between one parturition and the next the longer, that is to say, the mother has had to wait for her next conception, the greater is the excess of male births. Düsing therefore lays down the law: “Delayed impregnation gives rise to an excess of male births.”

═══════════╤════════════╤════════════╤════════════╤════════════╤═══════ Age of │ Leipzig. │ Dresden. │ Jena. │ Total Nos. │Sexual primiparæ. │Boys. Girls.│Boys. Girls.│Boys. Girls.│Boys. Girls.│ratio. ───────────┼────────────┼────────────┼────────────┼────────────┼─────── 1 │ 162 : 158 │ 194 : 178 │ 58 : 45 │ 414 : 381 │ 108.6 2 │ 366 : 307 │ 374 : 361 │ 168 : 145 │ 908 : 813 │ 111.6 3 │ 198 : 196 │ 207 : 194 │ 116 : 94 │ 521 : 484 │ 107.7 ───────────┼────────────┼────────────┼────────────┼────────────┼─────── 4 │ 127 : 109 │ 132 : 106 │ 59 : 45 │ 318 : 260 │} 115.7 5 │ 59 : 54 │ 55 : 54 │ 38 : 38 │ 152 : 146 │ „ ───────────┼────────────┼────────────┼────────────┼────────────┼─────── 6 │ 61 : 62 │ 52 : 49 │ 49 : 24 │ 162 : 135 │} 121.9 8, 9 and 10│ 18 : 16 │ 41 : 23 │ 16 : 24 │ 75 : 63 │ „ 11 and more│ 5 : 15 │ 12 : 9 │ 4 : 6 │ 41 : 30 │ „ ───────────┴────────────┴────────────┴────────────┴────────────┴─────── Totals: 4,903 births, 2,591 m.; 2,312 f.; sexual ratio = 112.06.

Bidder considers that his own observations entitle him to modify Ahlfeld’s dictum regarding the influence of age in primiparæ in giving rise to an excess of male births. He tabulates his results as follows:

═════════════════╤═════════════════╤═════════════════ AGE OF MOTHER. │Number of cases. │ Sexual ratio. ─────────────────┼─────────────────┼───────────────── 17 to 20 │ 80│ 122.2 20 to 22 │ 405│ 130.1 22 to 24 │ 369│ 109.9 24 to 26 │ 1,138│ 104.6 26 to 30 │ 2,049│ 105.5 30 to 32 │ 878│ 112.5 32 to 36 │ 1,120│ 119.6 36 to 39 │ 676│ 123.1 40 and upward │ 215│ 131.5 ═════════════════╧═════════════════╧═════════════════

and formulates the following thesis: Very young primiparæ give birth to an excess of boys; primiparæ in the first bloom of womanhood give birth to an excess of girls; later, however, as the age of the primiparæ increases the excess of male births soon reappears and rapidly increases.

Hofacker’s data and the researches of Hampe agree with those of Bidder in showing that to very young primiparæ, as well as to elderly primiparæ, an excess of boys is born. Among the offspring of 363 mothers, at ages varying from 16 to 26 years, Hofacker found the sexual ratio to be 121; among the offspring of 1,056 mothers, at ages 26 to 36, the ratio was 101; and among the offspring of 567 mothers at ages 36 to 46, the ratio was 111. Hampe tabulated 5,992 instances as follows:

═══════════════════════╤═══════════════════════╤═══════════════════════ AGE OF MOTHER. │ Number of instances. │ Sexual ratio. ───────────────────────┼───────────────────────┼─────────────────────── Below 20 years │ 56│ 107.7 20 to 25 years │ 871│ 90.6 25 to 30 years │ 1,633│ 114.9 30 to 35 years │ 1,631│ 108.3 35 to 40 years │ 1,185│ 117.1 Over 40 years │ 616│ 124.0 ═══════════════════════╧═══════════════════════╧═══════════════════════

We learn, therefore, that if the age of the progenitors is to be regarded as one of the causes by which sex is determined, we must take into consideration not only the relative ages of husband and wife but, in addition, the absolute age of the wife.

Goehlert undertook a statistical investigation in which the absolute age of the husband was taken into consideration as well as that of the wife. From this it appeared that the maximum sexual ratio was exhibited when the father was between the ages of 30 and 35 years. When the age of the mother is treated as the determining influence, we find the maximum sexual ratio in the offspring of mothers between the ages of 25 and 30 years. Goehlert believes, however, that the paternal influence is more powerful than the maternal in the determination of sex. The respective influences are compared in the following table:

══════════════╤═══════════════════════════════════════════════════════ AGE OF FATHER.│ AGE OF MOTHER. ──────────────┼─────────────┬─────────────┬─────────────┬───────────── „ │ 20 to 30 │ 30 to 40 │ Over 40 │ Totals. │ years. │ years. │ years. │ ──────────────┼─────────────┼─────────────┼─────────────┼───────────── 25 to 35 years│ 105.76│ 107.87│ 109.14│ 106.6 35 to 45 years│ 102.8│ 105.1│ 105.3│ 104.7 Over 45 years │ │ 104.3│ 103.9│ 109.1 In general │ 105.25│ 105.97│ 104.9│ 105.5 ══════════════╧═════════════╧═════════════╧═════════════╧═════════════

Geissler, studying the data obtainable regarding the sexual ratio during a 10–year period in the Kingdom of Saxony, ascertained that in families possessing two children or more there was a very definite distribution of the possible sex-combinations. Where there was an even number of children those families were in the majority in which the number of boys and girls was identical. If the number of children in the family is an unequal one, those combinations are most frequent in which the number of boys exceeds the number of girls by one; next in frequency are those combinations reversed to this, i. e., in which the number of girls exceeds the number of boys by one. All other combinations are comparatively infrequent in proportion as the discrepancy in number between boys and girls is larger. Rarest of all are families in which the children are all of the same sex; and among these, again, the most unusual are those consisting of boys only.

This distribution of the sex-combination is believed by Geissler to depend upon the fact that in the first birth and all the subsequent births there is generally speaking a slight advantage in favour of the male sex. It has not been proved that the sex of the first-born exercises a determining influence on the sex of the subsequent children. It does, however, seem clear that in the case of parents who have given birth in succession to several children of one sex only, there exists some definite obstacle to the procreation of children of the opposite sex. Putting these exceptions out of consideration, there seems to exist a tendency in the later births of a series toward the procreation, more especially of that sex which has been absent or deficient in the earlier births of the series. The strength of this equalizing tendency increases as soon as it has for the first time manifest itself. It is always greater when the sex deficient in the earlier births of the series has been the male.

I have myself undertaken a statistical investigation of the births occurring in the reigning families of Europe and in the families of the leading members of the aristocracy. The necessary particulars are to be obtained from the genealogical court calendars; and it is my belief that the data obtained regarding these uppermost strata of society are comparatively free from many sources of error by which the ordinary statistics of the subject are apt to be invalidated. For 556 marriages there were 1,972 births, comprising 1,023 boys and 949 girls, and thus exhibiting a sexual ratio of 107.7.

In relation to the relative ages of the parents, the following table was drawn up:

══════════════════════════════════════════════════╤══════╤══════╤══════ │ │ │Sexual │Boys. │Girls.│ratio. ──────────────────────────────────────────────────┼──────┼──────┼────── Husband older than wife by one to five years │ 294│ 283│ 103.8 Husband older than wife by more than five and less│ │ │ than ten years │ 327│ 306│ 106.8 Husband older than wife by more than ten and less │ │ │ than fifteen years │ 190│ 167│ 113.7 Husband older than wife by more than fifteen years│ 138│ 113│ 122.1 Husband same age as wife │ 34│ 42│ 80.9 Husband younger than wife │ 40│ 38│ 105.2 ══════════════════════════════════════════════════╧══════╧══════╧══════

From these figures we may deduce the following conclusions, which are not wholly concordant with the law of Hofacker and Sadler: When the husband is older than the wife the excess of male births among the offspring is greater than it is in the case of an average drawn from the offspring of all marriages (in my cases the difference was 111.8 as compared with 107.7). But a closer analysis shows the difference to be less simple than at first sight appears. If the husband is older than the wife by one to five years, the excess of male births among their offspring (103.8) is less than in the average of all marriages (107.7); the same is true of the offspring of marriages in which the husband is more than five and less than ten years older than the wife, though the difference here is very trifling (106.8 as compared with 107.7). It is not till we come to the offspring of marriages in which the husband is from ten to fifteen years older than the wife that the increase in the excess of male births becomes notable (113.7 as compared with 107.7); and when the husband is more than fifteen years older than the wife the excess of males is higher still (122.1).

If we arrange these data so as to show, in cases in which the husband is older than the wife, the additional influence of the absolute age of the wife, we obtain results which partially conflict with those of Bidder, as follows:

══════════════════════════════════════════════════╤══════╤══════╤══════ HUSBAND OLDER THAN WIFE. │ │ │Sexual │Boys. │Girls.│ratio. ──────────────────────────────────────────────────┼──────┼──────┼────── Wife’s age, 15 to 20 years │ 280│ 287│ 97.6 Wife’s age, 20 to 26 years │ 595│ 513│ 116.0 Wife’s age, 26 to 33 years │ 74│ 69│ 110.1 ══════════════════════════════════════════════════╧══════╧══════╧══════

Thus we see that when the wife is very young, i e., less than twenty years of age, even though the husband is older than the wife, there is among their offspring no excess of male births, but the contrary—a sexual ratio of 97.6 only. Most marked is the excess of boys in cases in which the husband is older than the wife, and the age of the wife is from twenty to twenty-five years. When the husband is older than the wife, and the wife’s age lies between twenty-five and thirty-two years, the excess of male births is not so great, though still considerable.

Hence it appears that the law of Hofacker and Sadler, which cannot be regarded as fully valid in the terms in which it was originally expressed, must be modified as follows: If the husband is at least 10 years older than the wife, and the latter is at an age when her reproductive capacity is at its maximum (twenty to twenty-five years), the offspring exhibit a notable excess of male births. There is still a considerable excess of male births in the offspring of marriages in which the husband is at least ten years older than the wife, and the wife is more than twenty-five years of age. On the other hand fewer boys are born than girls as the offspring of marriages in which, although the husband is older than the wife, the wife has not yet attained the age of maximum reproductive capacity—i. e., is less than twenty years of age. The excess of female births is most marked when the husband and wife are of the same age. When the wife is older than the husband there is a moderate excess of male births.

I admit, however, that the figures upon which I have based these conclusions are, like those of Hofacker, too few in number for the foundation of trustworthy inferences. The instances in my computation number 1,972; those in that of Hofacker, 1,996; but, as I have already remarked, there are reasons for believing that the data I have employed admit of the introduction of fewer sources of error.

The influence of the absolute age of the mother in the determination of sex having been statistically proved, many have inferred that this determination is not effected during the instant of fertilization, but occurs at a later stage of intra-uterine life, and is influenced by the manner in which the embryo is nourished by the maternal organism. It is suggested that elderly and immature mothers are unable to furnish the embryo with nutriment so well as those mothers who are at the age of maximum reproductive capacity, and that upon this fact depends the excess of male births in the latter case. (We shall return to this matter—the influence of deficient nutrition in relation to the excess of male births). But the proof of the fact that the absolute age of the father has also an influence in the determination of the sex of the offspring offers a ground for opposing this assumption that the sex of the embryo is determined during intra-uterine life subsequent to fertilization, and suggests that the father also exercises a determining influence in the origination of sex during the act of fertilization.

The absolute age of the husband seems also to have some influence upon the sexual ratio. The absolute age, like the relative age, of the father appears favourable to the procreation of a greater excess of boys. Thus, Hofacker found in 1,193 cases, in which the age of the father was from twenty-four to thirty-six years, that the sexual ratio was 100; in 683 cases in which the age of the father was from thirty-six to forty-eight years, the sexual ratio was 114; and in 105 cases, in which the age of the father was from forty-eight to sixty years, the sexual ratio was 169.

In investigations based upon larger collections of cases Schumann and Düsing have endeavoured to determine the variation in the sexual ratio according to the absolute age of the father.

Düsing examined the statistics of births in Norway, Alsace-Lorraine and Berlin, and from the data thus obtained he compiled the following table:

════════╤════════════════════╤════════════════════╤════════════════════ AGE OF │ 30 TO 35 YEARS. │ 25 TO 30 YEARS. │ 20 TO 25 YEARS. MOTHER. │ │ │ ────────┼──────┬──────┬──────┼──────┬──────┬──────┼──────┬──────┬────── AGE OF │Boys. │Girls.│Sexual│Boys. │Girls.│Sexual│Boys. │Girls.│Sexual FATHER. │ │ │ratio.│ │ │ratio.│ │ │ratio. ────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼────── 15 to 30│ 8,525│ 7,887│ 108.1│27,389│25,843│ 106.0│21,560│20,330│ 106.0 years │ │ │ │ │ │ │ │ │ 30 to 35│23,283│21,823│ 106.9│23,394│23,486│ 103.9│ 7,954│ 7,469│ 106.5 years │ │ │ │ │ │ │ │ │ 35 to 40│17,885│17,070│ 104.7│10,272│ 9,838│ 104.2│ 2,426│ 2,416│ 100.4 years │ │ │ │ │ │ │ │ │ ────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼────── 40 to 45│ 7,972│ 7,681│ 103.8│ 3,165│ 3,058│ 103.5│ }│ 1,100│ 105.0 years │ │ │ │ │ │ │ 1,154│ │ Over 45 │ 4,220│ 3,997│ 105.6│ 1,734│ 1,525│ 113.8│ „ │ „ │ „ years │ │ │ │ │ │ │ │ │ ────────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────

In this table we find the births arranged in relation to varying ages of the fathers and in relation to mothers whose ages are tabulated in three classes, the ages of the latter being those at which they are most prolific. The table shows clearly that the excess of boys is larger at the beginning and at the end of each column. Thus, the age of the mother remaining constant, young fathers and elderly fathers procreate a larger proportion of boys than do fathers of intermediate age.