Chapter C: Section CCXXXVIII: Increase of Population in General

That amid the thousand dangers which threaten the existence of the individual the species may endure, the Creator has endowed every class of organic beings with such reproductive power, and so much pleasure in propagating their kind, that if the action of these were entirely unrestricted, it would soon fill up the earth.[238-1] In the case of the human race, also, the physiological possibility of propagation has very wide limits.[238-2] It would be nothing extraordinary that a healthy pair, living in wedlock from the 20th to the 42nd year of the woman's life, that is, during the whole time of her full capacity to bear children, should rear six children to the age of puberty. This would, therefore, suffice to treble the population in a single generation; provided that all who had grown up should marry. According to Euler,[238-3] when the births were 5 per cent. and the deaths 2 per cent., the population doubled in not quite 24 years; when the increase was 2-1/2 per annum, in 28 years; when 2, in 35 years, and when 1-1/2 per cent. in 47 years.

The United States furnish us with a striking illustration of this doctrine, and on the grandest scale. There the natural increase of the white population, from 1790 to 1840, was 400.4 per cent.; that is in the first decade 33.9 per cent. of the population in 1790; in the second 33.1, in the third 32.1, in the fourth 30.9, in the fifth 29.6 per cent.[238-4] [238-5]

[Footnote 238-1: Thus, for instance, the sturgeon can,
according to _Leuckart_, produce 3,000,000 eggs in a year.
According to _Burdach_, the posterity of a pair of rabbits
may be over 1,000,000 in four years; and that of a
plant-louse, according to _Bonnet_, over a 1,000,000,000 in
a few weeks. The prolificacy of a species of animals is wont
to be greater in proportion as the structure-material
(_Bildungsmaterial_) saved within a given time during the
course of individual life, is greater, and as material wants
during the embryonic period are limited; also
(teleologically), in proportion as to the danger the
individual is exposed to. Compare _Leuckart_ in _R.
Wagner's_ physiolog. Wörterbuch, Art. Zeugung.
Teleologically, _Bastiat_ says: _cette surabondance parait
calculée partout en raison inverse de la sensibilité, de
l'intelligence et de la force avec laquelle chaque espèce
résiste à la déstruction_. (Harmonies, ch. 16.)]

[Footnote 238-2: The researches of modern physiology make it
probable that an ovum is detached from the ovaries at each
period of healthy menstruation. (_Bischoff_, Beweis der von
der Begattung unabhängigen periodischen Reifung und Lösung
der Eier bei den Säugethieren und Menschen, 1844.) It is
hardly possible to ascertain how many of these ova are
capable of fecundation. Among the animals, on which the
greater number of accurate observations have been made, that
is in the case of horses, it has been found that, in the two
districts of Prussia most favorably conditioned, of 100
mares that had been lined, 63.3 became pregnant, and 53.5
gave birth to live foals; in the rest of the Prussian
monarchy, the births were only 46 per cent. Compare
_Schubert_, Staatskunde, VII, 1, 98. In the Belgian _haras_
(places for breeding horses), between 1841 and 1850, about
30 per cent. of the "leaps" proved fruitful, from 2 to 3 per
cent. aborted, the rest were either probably or certainly
unfruitful. (_Horn._, Statist. Gemälde, 171.) In the human
species, also, the great number of first-born generated in
the first weeks of marriage, bears witness to a high degree
of procreative susceptibility.

On the other hand, the healthy male semen ejected during a
single act of coition contains innumerable germs, a very few
of which are sufficient to produce fecundation. (_Leuckart_,
loc. cit, 907.) According to _Oesterlen_, Handbuch der
medicischen Statistik, 1865, 196, from 10 to 20 per cent. of
all marriages were childless. In the United Kingdom, _Farr_,
report on the Census of 1851, estimated that in a population
of 27,511,000, there were 1,000,000 childless families, when
the term is allowed to embrace widows and widowers as well
as married couples.]

[Footnote 238-3: See the exhaustive table in _Euler_,
Mémoires de l'Académie de Berlin 1756, in _Süssmilch_,
Göttl. Ordnung, I, § 160. Bridge has constructed the
following formula:

Log. A = Log. P + n x Log.(1+(m-b)/mb). Here P stands for
the actually existing population, 1/m = the ratio between
the annual mortality and the number of the living, 1/b, the
ratio of the number of annual births to the number of the
living, n the number of years, A, the population at the end
of three years, the quantity sought for.]

[Footnote 238-4: _Tucker_, Progress of the United States,
89, ff. 98. Here deduction is already made of immigrants and
their posterity, who after subtracting the loss by
emigration back to the old country, amounted to over
1,000,000. It probably amounted to more yet. If, as
_Wappäus_ does (Bevölekerungsstatistik, 1859, I, 93, 122
ff.), we calculate the rate of increase per annum, we have
an average during the first decade of 2.89, during the
second of 2.83, the third of 2.74, the fourth of 2.52, the
seventh of 2.39, the eighth (1860-70) of probably 2.25 per
cent. On the still greater ratio of increase in earlier
times, see _Price_, Observations on reversionary Payments,
1769, 4 ed. 1783, I, 282 seq., I, 260.

It was nothing unheard of to see an old man with a living
posterity of 100. (_Franklin_, Observations concerning the
Increase of Mankind, and the Peopling of New Countries,
1751.) It is said that in the region about Contendas, in
Brazil, there were on from 70 to 80 births a mortality of
from 3 to 4 per annum (how long?), and an unfortunate birth
(_unglücklichen_) was scarcely ever heard of. Mothers 20
years of age had from 8 to 10 children; and one woman in the
fifties had a posterity of 204 living persons. (_Spix und
Martius_, Reise III, 525).]

[Footnote 238-5: Immense increase of the Israelites in
Egypt. (Genesis 46, 27; Numbers, 1.)]