An Essay on the Principle of Population

It appears clearly from the very valuable tables of mortality, which Sussmilch has collected, and which include periods of 50 or 60 years, that all the countries of Europe are subject to periodical sickly seasons, which check their increase; and very few are exempt from those great and wasting plagues which, once or twice perhaps in a century, sweep off the third or fourth part of their inhabitants. The way in which these periods of mortality affect all the general proportions of births, deaths, and marriages, is strikingly illustrated in the
tables for Prussia and Lithuania, from the year 1692 to the year 1757.
*59

The table, from which this is copied, contains the marriages, births and deaths for every particular year during the whole period; but to bring it into a smaller compass, I have retained only the general average drawn from the shorter periods of five and four years, except where the numbers for the individual years presented any fact worthy of particular observation. The year 1711, immediately succeeding the great plague, is not included by Sussmilch in any general average; but he has given the particular numbers, and if they be accurate they shew the very sudden and prodigious effect of a great mortality on the number of marriages.

Sussmilch calculates that above one third of the people was destroyed by the plague; and yet, notwithstanding this great diminution of the population, it will appear by a reference to the table, that the number of marriages in the year 1711 was very nearly double the average of the six years preceding the plague.
*60 To produce this effect, we may suppose that almost all who were at the age of puberty were induced, from the demand for labour and the number of vacant employments, immediately to marry. This immense number of marriages in the year could not possibly be accompanied by a great proportional number of births, because we cannot suppose that the new marriages could each yield more than one birth in the year, and the rest must come from the marriages which had continued unbroken through the plague. We cannot therefore be surprised that the proportion of births to marriages in this year should be only 2.7 to 1, or 27 to 10. But though the proportion of births to marriages could not be great; yet, on account of the extraordinary number of marriages, the absolute number of births must be great; and as the number of deaths would naturally be small, the proportion of births to deaths is prodigious, being 320 to 100; an excess of births as great, perhaps, as has ever been known in America.

In the next year, 1712, the number of marriages must of course diminish exceedingly; because, nearly all who were at the age of puberty having married the year before, the marriages of this year would be supplied principally by those who had arrived at this age, subsequent to the plague. Still, however, as all who were marriageable had not probably married the year before, the number of marriages in the year 1712 is great in proportion to the population; and, though not much more than half of the number which took place during the preceding year, is greater than the average number in the last period before the plague. The proportion of births to marriages in 1712, though greater than in the preceding year, on account of the smaller comparative number of marriages, is, with reference to other countries, not great, being as 3.6 to 1, or 3.6 to 10. But the proportion of births to deaths, though less than in the preceding year, when so very large a proportion of the people married, is, with reference to other countries, still unusually great, being as 220 to 100; an excess of births, which, calculated on a mortality of 1 in 36, would double the population of a country (according to
Table I. page 496) in 21 1/8 years.

From this period the number of annual marriages begins to be regulated by the diminished population, and of course to sink considerably below the average number of marriages before the plague, depending principally on the number of persons rising annually to a marriageable state. In the year 1720, about nine or ten years after the plague, the number of annual marriages, either from accident, or the beginning operation of the preventive check, is the smallest; and it is at this time that the proportion of births to marriages rises very high. In the period from 1717 to 1721 the proportion, as appears by the table, is 49 to 10; and in the particular years 1719 and 1720, it is 50 to 10 and 55 to 10.

Sussmilch draws the attention of his readers to the fruitfulness of marriages in Prussia after the plague, and mentions the proportion of 50 annual births to 10 annual marriages as a proof of it. There are the best reasons from the general average for supposing that the marriages in Prussia at this time were very fruitful; but certainly the proportion of this individual year, or even period, is not a sufficient proof of it, being evidently caused by a smaller number of marriages taking place in the year, and not by a greater number of births.
*61 In the two years immediately succeeding the plague, when the excess of births above the deaths was so astonishing, the births bore a small proportion to the marriages; and according to the usual mode of calculation, it would have followed that each marriage yielded only 2.7 or 3.6 children. In the last period of the table, (from 1752 to 1756,) the births are to the marriages as 5 to 1, and in the individual year 1756, as 6.1 to 1: and yet during this period the births are to the deaths only as 148 to 100, which could not have been the case, if the high proportion of births to marriages had indicated a much greater number of births than usual, instead of a smaller number of marriages.

The variations in the proportion of births to deaths, in the different periods of 64 years included in the table, deserve particular attention. If we were to take an average of the four years immediately succeeding the plague, the births would be to the deaths in the proportion of above 22 to 10, which, supposing the mortality to be 1 in 36, would double the population in twenty-one years. If we take the twenty years from 1711 to 1731, the average proportion of the births to deaths will appear to be about 17 to 10, a proportion which (according to
Table I. page 496) would double the population in about thirty-five years. But if, instead of 20 years, we were to take the whole period of 64 years, the average proportion of births to deaths turns out to be but a little more than 12 to 10; a proportion which would not double the population in less than 125 years. If we were to include the mortality of the plague, or even of the epidemic years 1736 and 1737, in too short a period, the deaths might exceed the births, and the population would appear to be decreasing.

Sussmilch thinks that, instead of 1 in 36, the mortality in Prussia, after the plague, might be 1 in 38; and it may appear perhaps to some of my readers, that the plenty occasioned by such an event ought to make a still greater difference. Dr. Short has particularly remarked that an extraordinary healthiness generally succeeds any very great mortality;
*62 and I have no doubt that the observation is just, comparing similar ages together. But, under the most favourable circumstances, infants under three years are more subject to death than at other ages; and the extraordinary proportion of children which usually follows a very great mortality, counterbalances at first the natural healthiness of the period, and prevents it from making much difference in the general mortality.

If we divide the population of Prussia after the plague, by the number of deaths in the year 1711, it will appear, that the mortality was nearly 1 in 31, and was therefore increased rather than diminished, owing to the prodigious number of children born in that year. But this greater mortality would certainly cease, as soon as these children began to rise into the firmer stages of life, and then probably Sussmilch’s observations would be just. In general, however, we shall observe that a great previous mortality produces a more sensible effect on the births than on the deaths. By referring to the table it will appear, that the number of annual deaths regularly increases with the increasing population, and nearly keeps up the same relative proportion all the way through. But the number of annual births is not very different during the whole period, though in this time the population had more than doubled itself; and therefore the
proportion of births to the whole population, at first and at last, must have changed in an extraordinary degree.

It will appear therefore how liable we should be to err in assuming a given proportion of births, for the purpose of estimating the past population of any country. In the present instance, it would have led to the conclusion, that the population was scarcely diminished by the plague, although from the number of deaths it was known to be diminished one third.

Variations of the same kind, though not in the same degree, appear in the proportions of births, deaths and marriages, in all the tables which Sussmilch has collected; and as writers on these subjects have been too apt to form calculations for past and future times from the proportions of a few years, it may be useful to draw the attention of the reader to a few more instances of such variations.

In the Churmark of Brandenburgh,
*63 during 15 years, ending with 1712, the proportion of births to deaths was nearly 17 to 10. For 6 years, ending with 1718, the proportion sunk to 13 to 10; for 4 years, ending with 1752, it was only 11 to 10; and for 4 years, ending with 1756, 12 to 10. For 3 years, ending with 1759, the deaths very greatly exceeded the births. The proportion of the births to the whole population is not given; but it is not probable that the great variations observable in the proportion of births to deaths should have arisen solely from the variations in the deaths. The proportion of births to marriages is tolerably uniform, the extremes being only 38 to 10 and 35 to 10, and the mean about 37 to 10. In this table no very great epidemics occur till the 3 years beginning with 1757, and beyond this period the lists are not continued.

In the dukedom of Pomerania,
*64 the average proportion of births to deaths for 60 years (from 1694 to 1756 both included) was 138 to 100; but in some of the periods of six years it was as high as 177 to 100, and 155 to 100. In others it sunk as low as 124 to 100, and 130 to 100. The extremes in the proportions of births to marriages of the different periods of 5 and 6 years, were 36 to 10 and 43 to 10, and the mean of the 60 years about 38 to 10. Epidemic years appear to have occurred occasionally, in three of which the deaths exceeded the births; but this temporary diminution of population produced no corresponding diminution of births, and the two individual years which contain the greatest proportion of marriages in the whole table occur, one in the year after, and the other two years after epidemics. The excess of deaths however was not great till the three years ending with 1759, with which the table concludes.

In the Neumark of Brandenburgh,
*65 for 60 years, from 1695 to 1756 both included, the average proportion of births to deaths in the first 30 years was 148 to 100, in the last 30 years 127 to 100, in the whole 60 years 136 to 100. In some periods of 5 years it was as high as 171 and 167 to 100. In others as low as 118 and 128 to 100. For 5 years ending with 1726, the yearly average of births was 7012; for 5 years ending with 1746, it was 6927, from which, judging by the births, we might infer that the population had decreased in this interval of 20 years; but it appears from the average proportion of births and deaths during this period, that it must have considerably increased, notwithstanding the intervention of some epidemic years. The proportion of births to the whole population must therefore have decidedly changed. Another interval of 20 years in the same tables gives a similar result, both with regard to the births and marriages. The extremes of the proportion of births to marriages are 34 to 10, and 42 to 10, the mean about 38 to 10. The 3 years beginning with 1757, were, as in the other tables, very fatal years.

In the dukedom of Magdeburgh,
*66 during 64 years ending with 1756, the average proportion of births to deaths was 123 to 100; in the first 28 years of the period 142 to 100, and in the last 34 years only 112 to 100; during one period of 5 years it was as high as 170 to 100; and in two periods the deaths exceeded the births. Slight epidemics appear to be interspersed rather thickly throughout the table. In the two instances, where three or four occur in successive years and diminish the population, they are followed by an increase of marriages and births. The extremes of the proportions of births to marriages are 42 to 10 and 34 to 10, and the mean of the 64 years 39 to 10. On this table Sussmilch remarks, that though the average number of deaths shews an increased population of one third from 1715 or 1720, yet the births and marriages would prove it to be stationary, or even declining. In drawing this conclusion however, he adds the three epidemic years ending with 1759, during which both the marriages and births seem to have diminished.

In the principality of Halberstadt,
*67 the average proportion of births to deaths for 68 years, ending with 1756, was 124 to 100; but in some periods of 5 years it was as high as 160 to 100, and in others as low as 110 to 100. The increase in the whole 68 years was considerable, and yet for 5 years ending with 1723, the average number of births was 2818; and for 4 years ending with 1750, 2628, from which it would appear that the population in 27 years had considerably diminished. A similar appearance occurs with regard to the marriages during a period of 32 years. In the 5 years ending with 1718, they were 727; in the 5 years ending with 1750, 689. During both these periods the proportion of deaths would have shewn a considerable increase. Epidemics seem to have occurred frequently; and in almost all the instances, in which they were such as for the deaths to exceed the births, they were immediately succeeded by a more than usual proportion of marriages, and in a few years by an increased proportion of births. The greatest number of marriages in the whole table occurs in the year 1751, after an epidemic in the year 1750, in which the deaths had exceeded the births above one third, and the four or five following years contain the largest proportion of births. The extremes of the proportions of births to marriages are 42 to 10 and 34 to 10; the mean of the 68 years 38 to 10.

The remaining tables contain similar results; but these will be sufficient to shew the variations which are continually occurring in the proportions of the births and marriages, as well as of the deaths, to the whole population.

It will be observed that the least variable of the proportions is that which the births and marriages bear to each other; and the obvious reason is, that this proportion is principally influenced by the prolifickness of marriages, which will not of course be subject to great changes. We can hardly indeed suppose, that the prolifickness of marriages should vary so much as the different proportions of births to marriages in the tables. Nor is it necessary that it should, as another cause will contribute to produce the same effect. The births which are contemporary with the marriages of any particular year, belong principally to marriages which had taken place some years before; and therefore, if for four or five years a large proportion of marriages were to take place; and then accidentally for one or two years a small proportion, the effect would be a large proportion of births to marriages in the registers during these one or two years; and on the contrary, if for four or five years few marriages comparatively were to take place, and then for one or two years a great number, the effect would be a small proportion of births to marriages in the registers. This was strikingly illustrated in the
table for Prussia and Lithuania, and would be confirmed by an inspection of all the other tables collected by Sussmilch; in which it appears that the extreme proportions of births to marriages are generally more affected by the number of marriages than the number of births, and consequently arise more from the variations in the disposition or encouragement to matrimony, than from the variations in the prolifickness of marriages.

The common epidemical years which are interspersed throughout these tables, will not of course have the same effects on the marriages and births as the great plague in the table for Prussia; but in proportion to their magnitude, their operation will in general be found to be similar. From the registers of many other countries, and particularly of towns, it appears that the visitations of the plague were frequent at the latter end of the 17th, and the beginning of the 18th centuries.

In contemplating the plagues and sickly seasons which occur in these tables after a period of rapid increase, it is impossible not to be impressed with the idea, that the number of inhabitants had in these instances exceeded the food and the accommodations necessary to preserve them in health. The mass of the people would, upon this supposition, be obliged to live worse, and a greater number of them would be crowded together in one house; and these natural causes would evidently contribute to produce sickness, even though the country, absolutely considered, might not be crowded and populous. In a country even thinly inhabited, if an increase of population take place before more food is raised, and more houses are built, the inhabitants must be distressed for room and subsistence. If in the Highlands of Scotland, for the next ten or twelve years, the marriages were to be either more frequent or more prolific, and no emigration were to take place, instead of five to a cottage, there might be seven; and this, added to the necessity of worse living, would evidently have a most unfavourable effect on the health of the common people.