<p>SUPPLEMENT ON THE PROPORTIONAL NUMBERS OF THE TWO SEXES IN ANIMALS BELONGING TO
VARIOUS CLASSES.</p>
<p>As no one, as far as I can discover, has paid attention to the relative numbers
of the two sexes throughout the animal kingdom, I will here give such materials
as I have been able to collect, although they are extremely imperfect. They
consist in only a few instances of actual enumeration, and the numbers are not
very large. As the proportions are known with certainty only in mankind, I will
first give them as a standard of comparison.</p>
<h3>MAN.</h3>
<p>In England during ten years (from 1857 to 1866) the average number of children
born alive yearly was 707,120, in the proportion of 104.5 males to 100 females.
But in 1857 the male births throughout England were as 105.2, and in 1865 as
104.0 to 100. Looking to separate districts, in Buckinghamshire (where about
5000 children are annually born) the MEAN proportion of male to female births,
during the whole period of the above ten years, was as 102.8 to 100; whilst in
N. Wales (where the average annual births are 12,873) it was as high as 106.2
to 100. Taking a still smaller district, viz., Rutlandshire (where the annual
births average only 739), in 1864 the male births were as 114.6, and in 1862 as
only 97.0 to 100; but even in this small district the average of the 7385
births during the whole ten years, was as 104.5 to 100: that is in the same
ratio as throughout England. (48. ‘Twenty-ninth Annual Report of the
Registrar-General for 1866.’ In this report (p. xii.) a special decennial
table is given.) The proportions are sometimes slightly disturbed by unknown
causes; thus Prof. Faye states “that in some districts of Norway there
has been during a decennial period a steady deficiency of boys, whilst in
others the opposite condition has existed.” In France during forty-four
years the male to the female births have been as 106.2 to 100; but during this
period it has occurred five times in one department, and six times in another,
that the female births have exceeded the males. In Russia the average
proportion is as high as 108.9, and in Philadelphia in the United States as
110.5 to 100. (49. For Norway and Russia, see abstract of Prof. Faye’s
researches, in ‘British and Foreign Medico-Chirurg. Review,’ April
1867, pp. 343, 345. For France, the ‘Annuaire pour l’An
1867,’ p. 213. For Philadelphia, Dr. Stockton Hough, ‘Social
Science Assoc.’ 1874. For the Cape of Good Hope, Quetelet as quoted by
Dr. H.H. Zouteveen, in the Dutch Translation of this work (vol. i. p. 417),
where much information is given on the proportion of the sexes.) The average
for Europe, deduced by Bickes from about seventy million births, is 106 males
to 100 females. On the other hand, with white children born at the Cape of Good
Hope, the proportion of males is so low as to fluctuate during successive years
between 90 and 99 males for every 100 females. It is a singular fact that with
Jews the proportion of male births is decidedly larger than with Christians:
thus in Prussia the proportion is as 113, in Breslau as 114, and in Livonia as
120 to 100; the Christian births in these countries being the same as usual,
for instance, in Livonia as 104 to 100. (50. In regard to the Jews, see M.
Thury, ‘La Loi de Production des Sexes,’ 1863, p. 25.)</p>
<p>Prof. Faye remarks that “a still greater preponderance of males would be
met with, if death struck both sexes in equal proportion in the womb and during
birth. But the fact is, that for every 100 still-born females, we have in
several countries from 134.6 to 144.9 still-born males. During the first four
or five years of life, also, more male children die than females, for example
in England, during the first year, 126 boys die for every 100 girls—a
proportion which in France is still more unfavourable.” (51.
‘British and Foreign Medico-Chirurg. Review,’ April 1867, p. 343.
Dr. Stark also remarks (‘Tenth Annual Report of Births, Deaths, etc., in
Scotland,’ 1867, p. xxviii.) that “These examples may suffice to
show that, at almost every stage of life, the males in Scotland have a greater
liability to death and a higher death-rate than the females. The fact, however,
of this peculiarity being most strongly developed at that infantile period of
life when the dress, food, and general treatment of both sexes are alike, seems
to prove that the higher male death-rate is an impressed, natural, and
constitutional peculiarity due to sex alone.”) Dr. Stockton Hough
accounts for these facts in part by the more frequent defective development of
males than of females. We have before seen that the male sex is more variable
in structure than the female; and variations in important organs would
generally be injurious. But the size of the body, and especially of the head,
being greater in male than female infants is another cause: for the males are
thus more liable to be injured during parturition. Consequently the still-born
males are more numerous; and, as a highly competent judge, Dr. Crichton Browne
(52. ‘West Riding Lunatic Asylum Reports,’ vol. i. 1871, p. 8. Sir
J. Simpson has proved that the head of the male infant exceeds that of the
female by 3/8ths of an inch in circumference, and by 1/8th in transverse
diameter. Quetelet has shewn that woman is born smaller than man; see Dr.
Duncan, ‘Fecundity, Fertility, and Sterility,’ 1871, p. 382.),
believes, male infants often suffer in health for some years after birth. Owing
to this excess in the death-rate of male children, both at birth and for some
time subsequently, and owing to the exposure of grown men to various dangers,
and to their tendency to emigrate, the females in all old-settled countries,
where statistical records have been kept, are found to preponderate
considerably over the males. (53. With the savage Guaranys of Paraguay,
according to the accurate Azara (‘Voyages dans l’Amerique
merid.’ tom. ii. 1809, pp. 60, 179), the women are to the men in the
proportion of 14 to 13.)</p>
<p>It seems at first sight a mysterious fact that in different nations, under
different conditions and climates, in Naples, Prussia, Westphalia, Holland,
France, England and the United States, the excess of male over female births is
less when they are illegitimate than when legitimate. (54. Babbage,
‘Edinburgh Journal of Science,’ 1829, vol. i. p. 88; also p. 90, on
still-born children. On illegitimate children in England, see ‘Report of
Registrar-General for 1866,’ p. xv.) This has been explained by different
writers in many different ways, as from the mothers being generally young, from
the large proportion of first pregnancies, etc. But we have seen that male
infants, from the large size of their heads, suffer more than female infants
during parturition; and as the mothers of illegitimate children must be more
liable than other women to undergo bad labours, from various causes, such as
attempts at concealment by tight lacing, hard work, distress of mind, etc.,
their male infants would proportionably suffer. And this probably is the most
efficient of all the causes of the proportion of males to females born alive
being less amongst illegitimate children than amongst the legitimate. With most
animals the greater size of the adult male than of the female, is due to the
stronger males having conquered the weaker in their struggles for the
possession of the females, and no doubt it is owing to this fact that the two
sexes of at least some animals differ in size at birth. Thus we have the
curious fact that we may attribute the more frequent deaths of male than female
infants, especially amongst the illegitimate, at least in part to sexual
selection.</p>
<p>It has often been supposed that the relative age of the two parents determine
the sex of the offspring; and Prof. Leuckart (55. Leuckart, in Wagner
‘Handwörterbuch der Phys.’ B. iv. 1853, s. 774.) has advanced what
he considers sufficient evidence, with respect to man and certain domesticated
animals, that this is one important though not the sole factor in the result.
So again the period of impregnation relatively to the state of the female has
been thought by some to be the efficient cause; but recent observations
discountenance this belief. According to Dr. Stockton Hough (56. ‘Social
Science Association of Philadelphia,’ 1874.), the season of the year, the
poverty or wealth of the parents, residence in the country or in cities, the
crossing of foreign immigrants, etc., all influence the proportion of the
sexes. With mankind, polygamy has also been supposed to lead to the birth of a
greater proportion of female infants; but Dr. J. Campbell (57.
‘Anthropological Review,’ April 1870, p. cviii.) carefully attended
to this subject in the harems of Siam, and concludes that the proportion of
male to female births is the same as from monogamous unions. Hardly any animal
has been rendered so highly polygamous as the English race-horse, and we shall
immediately see that his male and female offspring are almost exactly equal in
number. I will now give the facts which I have collected with respect to the
proportional numbers of the sexes of various animals; and will then briefly
discuss how far selection has come into play in determining the result.</p>
<h3>HORSES.</h3>
<p>Mr. Tegetmeier has been so kind as to tabulate for me from the ‘Racing
Calendar’ the births of race-horses during a period of twenty-one years,
viz., from 1846 to 1867; 1849 being omitted, as no returns were that year
published. The total births were 25,560 (58. During eleven years a record was
kept of the number of mares which proved barren or prematurely slipped their
foals; and it deserves notice, as shewing how infertile these highly-nurtured
and rather closely-interbred animals have become, that not far from one-third
of the mares failed to produce living foals. Thus during 1866, 809 male colts
and 816 female colts were born, and 743 mares failed to produce offspring.
During 1867, 836 males and 902 females were born, and 794 mares failed.),
consisting of 12,763 males and 12,797 females, or in the proportion of 99.7
males to 100 females. As these numbers are tolerably large, and as they are
drawn from all parts of England, during several years, we may with much
confidence conclude that with the domestic horse, or at least with the
race-horse, the two sexes are produced in almost equal numbers. The
fluctuations in the proportions during successive years are closely like those
which occur with mankind, when a small and thinly-populated area is considered;
thus in 1856 the male horses were as 107.1, and in 1867 as only 92.6 to 100
females. In the tabulated returns the proportions vary in cycles, for the males
exceeded the females during six successive years; and the females exceeded the
males during two periods each of four years; this, however, may be accidental;
at least I can detect nothing of the kind with man in the decennial table in
the Registrar’s Report for 1866.</p>
<h3>DOGS.</h3>
<p>During a period of twelve years, from 1857 to 1868, the births of a large
number of greyhounds, throughout England, were sent to the ‘Field’
newspaper; and I am again indebted to Mr. Tegetmeier for carefully tabulating
the results. The recorded births were 6878, consisting of 3605 males and 3273
females, that is, in the proportion of 110.1 males to 100 females. The greatest
fluctuations occurred in 1864, when the proportion was as 95.3 males, and in
1867, as 116.3 males to 100 females. The above average proportion of 110.1 to
100 is probably nearly correct in the case of the greyhound, but whether it
would hold with other domesticated breeds is in some degree doubtful. Mr.
Cupples has enquired from several great breeders of dogs, and finds that all
without exception believe that females are produced in excess; but he suggests
that this belief may have arisen from females being less valued, and from the
consequent disappointment producing a stronger impression on the mind.</p>
<h3>SHEEP.</h3>
<p>The sexes of sheep are not ascertained by agriculturists until several months
after birth, at the period when the males are castrated; so that the following
returns do not give the proportions at birth. Moreover, I find that several
great breeders in Scotland, who annually raise some thousand sheep, are firmly
convinced that a larger proportion of males than of females die during the
first year or two. Therefore the proportion of males would be somewhat larger
at birth than at the age of castration. This is a remarkable coincidence with
what, as we have seen, occurs with mankind, and both cases probably depend on
the same cause. I have received returns from four gentlemen in England who have
bred Lowland sheep, chiefly Leicesters, during the last ten to sixteen years;
they amount altogether to 8965 births, consisting of 4407 males and 4558
females; that is in the proportion of 96.7 males to 100 females. With respect
to Cheviot and black-faced sheep bred in Scotland, I have received returns from
six breeders, two of them on a large scale, chiefly for the years 1867-1869,
but some of the returns extend back to 1862. The total number recorded amounts
to 50,685, consisting of 25,071 males and 25,614 females or in the proportion
of 97.9 males to 100 females. If we take the English and Scotch returns
together, the total number amounts to 59,650, consisting of 29,478 males and
30,172 females, or as 97.7 to 100. So that with sheep at the age of castration
the females are certainly in excess of the males, but probably this would not
hold good at birth. (59. I am much indebted to Mr. Cupples for having procured
for me the above returns from Scotland, as well as some of the following
returns on cattle. Mr. R. Elliot, of Laighwood, first called my attention to
the premature deaths of the males, —a statement subsequently confirmed by
Mr. Aitchison and others. To this latter gentleman, and to Mr. Payan, I owe my
thanks for large returns as to sheep.)</p>
<p>Of CATTLE I have received returns from nine gentlemen of 982 births, too few to
be trusted; these consisted of 477 bull-calves and 505 cow-calves; i.e., in the
proportion of 94.4 males to 100 females. The Rev. W.D. Fox informs me that in
1867 out of 34 calves born on a farm in Derbyshire only one was a bull. Mr.
Harrison Weir has enquired from several breeders of PIGS, and most of them
estimate the male to the female births as about 7 to 6. This same gentleman has
bred RABBITS for many years, and has noticed that a far greater number of bucks
are produced than does. But estimations are of little value.</p>
<p>Of mammalia in a state of nature I have been able to learn very little. In
regard to the common rat, I have received conflicting statements. Mr. R.
Elliot, of Laighwood, informs me that a rat-catcher assured him that he had
always found the males in great excess, even with the young in the nest. In
consequence of this, Mr. Elliot himself subsequently examined some hundred old
ones, and found the statement true. Mr. F. Buckland has bred a large number of
white rats, and he also believes that the males greatly exceed the females. In
regard to Moles, it is said that “the males are much more numerous than
the females” (60. Bell, ‘History of British Quadrupeds,’ p.
100.): and as the catching of these animals is a special occupation, the
statement may perhaps be trusted. Sir A. Smith, in describing an antelope of S.
Africa (61. ‘Illustrations of the Zoology of S. Africa,’ 1849, pl.
29.) (Kobus ellipsiprymnus), remarks, that in the herds of this and other
species, the males are few in number compared with the females: the natives
believe that they are born in this proportion; others believe that the younger
males are expelled from the herds, and Sir A. Smith says, that though he has
himself never seen herds consisting of young males alone, others affirm that
this does occur. It appears probable that the young when expelled from the
herd, would often fall a prey to the many beasts of prey of the country.</p>
<h3>BIRDS.</h3>
<p>With respect to the FOWL, I have received only one account, namely, that out of
1001 chickens of a highly-bred stock of Cochins, reared during eight years by
Mr. Stretch, 487 proved males and 514 females; i.e., as 94.7 to 100. In regard
to domestic pigeons there is good evidence either that the males are produced
in excess, or that they live longer; for these birds invariably pair, and
single males, as Mr. Tegetmeier informs me, can always be purchased cheaper
than females. Usually the two birds reared from the two eggs laid in the same
nest are a male and a female; but Mr. Harrison Weir, who has been so large a
breeder, says that he has often bred two cocks from the same nest, and seldom
two hens; moreover, the hen is generally the weaker of the two, and more liable
to perish.</p>
<p>With respect to birds in a state of nature, Mr. Gould and others (62. Brehm
(‘Thierleben,’ B. iv. s. 990) comes to the same conclusion.) are
convinced that the males are generally the more numerous; and as the young
males of many species resemble the females, the latter would naturally appear
to be the more numerous. Large numbers of pheasants are reared by Mr. Baker of
Leadenhall from eggs laid by wild birds, and he informs Mr. Jenner Weir that
four or five males to one female are generally produced. An experienced
observer remarks (63. On the authority of L. Lloyd, ‘Game Birds of
Sweden,’ 1867, pp. 12, 132.), that in Scandinavia the broods of the
capercailzie and black-cock contain more males than females; and that with the
Dal-ripa (a kind of ptarmigan) more males than females attend the leks or
places of courtship; but this latter circumstance is accounted for by some
observers by a greater number of hen birds being killed by vermin. From various
facts given by White of Selborne (64. ‘Nat. Hist. of Selborne,’
letter xxix. edit. of 1825, vol. i. p. 139.), it seems clear that the males of
the partridge must be in considerable excess in the south of England; and I
have been assured that this is the case in Scotland. Mr. Weir on enquiring from
the dealers, who receive at certain seasons large numbers of ruffs (Machetes
pugnax), was told that the males are much the more numerous. This same
naturalist has also enquired for me from the birdcatchers, who annually catch
an astonishing number of various small species alive for the London market, and
he was unhesitatingly answered by an old and trustworthy man, that with the
chaffinch the males are in large excess: he thought as high as 2 males to 1
female, or at least as high as 5 to 3. (65. Mr. Jenner Weir received similar
information, on making enquiries during the following year. To shew the number
of living chaffinches caught, I may mention that in 1869 there was a match
between two experts, and one man caught in a day 62, and another 40, male
chaffinches. The greatest number ever caught by one man in a single day was
70.) The males of the blackbird, he likewise maintained, were by far the more
numerous, whether caught by traps or by netting at night. These statements may
apparently be trusted, because this same man said that the sexes are about
equal with the lark, the twite (Linaria montana), and goldfinch. On the other
hand, he is certain that with the common linnet, the females preponderate
greatly, but unequally during different years; during some years he has found
the females to the males as four to one. It should, however, be borne in mind,
that the chief season for catching birds does not begin till September, so that
with some species partial migrations may have begun, and the flocks at this
period often consist of hens alone. Mr. Salvin paid particular attention to the
sexes of the humming-birds in Central America, and is convinced that with most
of the species the males are in excess; thus one year he procured 204 specimens
belonging to ten species, and these consisted of 166 males and of only 38
females. With two other species the females were in excess: but the proportions
apparently vary either during different seasons or in different localities; for
on one occasion the males of Campylopterus hemileucurus were to the females as
5 to 2, and on another occasion (66. ‘Ibis,’ vol. ii. p. 260, as
quoted in Gould’s ‘Trochilidae,’ 1861, p. 52. For the
foregoing proportions, I am indebted to Mr. Salvin for a table of his results.)
in exactly the reversed ratio. As bearing on this latter point, I may add, that
Mr. Powys found in Corfu and Epirus the sexes of the chaffinch keeping apart,
and “the females by far the most numerous”; whilst in Palestine Mr.
Tristram found “the male flocks appearing greatly to exceed the female in
number.” (67. ‘Ibis,’ 1860, p. 137; and 1867, p. 369.) So
again with the Quiscalus major, Mr. G. Taylor says, that in Florida there were
“very few females in proportion to the males,” (68.
‘Ibis,’ 1862, p. 187.) whilst in Honduras the proportion was the
other way, the species there having the character of a polygamist.</p>
<h3>FISH.</h3>
<p>With fish the proportional numbers of the sexes can be ascertained only by
catching them in the adult or nearly adult state; and there are many
difficulties in arriving at any just conclusion. (69. Leuckart quotes Bloch
(Wagner, ‘Handwörterbuch der Phys.’ B. iv. 1853, s. 775), that with
fish there are twice as many males as females.) Infertile females might readily
be mistaken for males, as Dr. Gunther has remarked to me in regard to trout.
With some species the males are believed to die soon after fertilising the ova.
With many species the males are of much smaller size than the females, so that
a large number of males would escape from the same net by which the females
were caught. M. Carbonnier (70. Quoted in the ‘Farmer,’ March 18,
1869, p. 369.), who has especially attended to the natural history of the pike
(Esox lucius), states that many males, owing to their small size, are devoured
by the larger females; and he believes that the males of almost all fish are
exposed from this same cause to greater danger than the females. Nevertheless,
in the few cases in which the proportional numbers have been actually observed,
the males appear to be largely in excess. Thus Mr. R. Buist, the superintendent
of the Stormontfield experiments, says that in 1865, out of 70 salmon first
landed for the purpose of obtaining the ova, upwards of 60 were males. In 1867
he again “calls attention to the vast disproportion of the males to the
females. We had at the outset at least ten males to one female.”
Afterwards females sufficient for obtaining ova were procured. He adds,
“from the great proportion of the males, they are constantly fighting and
tearing each other on the spawning-beds.” (71. ‘The Stormontfield
Piscicultural Experiments,’ 1866, p. 23. The ‘Field’
newspaper, June 29, 1867.) This disproportion, no doubt, can be accounted for
in part, but whether wholly is doubtful, by the males ascending the rivers
before the females. Mr. F. Buckland remarks in regard to trout, that “it
is a curious fact that the males preponderate very largely in number over the
females. It INVARIABLY happens that when the first rush of fish is made to the
net, there will be at least seven or eight males to one female found captive. I
cannot quite account for this; either the males are more numerous than the
females, or the latter seek safety by concealment rather than flight.” He
then adds, that by carefully searching the banks sufficient females for
obtaining ova can be found. (72. ‘Land and Water,’ 1868, p. 41.)
Mr. H. Lee informs me that out of 212 trout, taken for this purpose in Lord
Portsmouth’s park, 150 were males and 62 females.</p>
<p>The males of the Cyprinidae likewise seem to be in excess; but several members
of this Family, viz., the carp, tench, bream and minnow, appear regularly to
follow the practice, rare in the animal kingdom, of polyandry; for the female
whilst spawning is always attended by two males, one on each side, and in the
case of the bream by three or four males. This fact is so well known, that it
is always recommended to stock a pond with two male tenches to one female, or
at least with three males to two females. With the minnow, an excellent
observer states, that on the spawning-beds the males are ten times as numerous
as the females; when a female comes amongst the males, “she is
immediately pressed closely by a male on each side; and when they have been in
that situation for a time, are superseded by other two males.” (73.
Yarrell, ‘Hist. British Fishes,’ vol. i. 1826, p. 307; on the
Cyprinus carpio, p. 331; on the Tinca vulgaris, p. 331; on the Abramis brama,
p. 336. See, for the minnow (Leuciscus phoxinus), ‘Loudon’s
Magazine of Natural History,’ vol. v. 1832, p. 682.)</p>
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