3. Growth of a Population of Yeast Cells (After Pearl)
Fig. 4. Growth of a Population of Fruit Flies in a Bottle (After Pearl)
Fig. 5. Growth of the Population of Sweden (After Pearl)
This demonstration does not conform so readily with the processes of our human logic. For human populations are subject to plagues and wars, to emigration and immigration, to birth-control movements and counter birth-control movements. They grow under conditions that seem far removed from the controlled environment of Drosophila in a test tube. And yet, as Pearl showed:
Sweden has grown in a manner which, in its quantitative relations at least, is essentially like the manner in which a population of yeast cells grows. . . . Except for the amount of time covered by the observations, this curve for the United States is strikingly like that of Sweden. . . . For France . . . the growth has evidently followed, during the epoch or cycle in which it now is, the same basic law as that of Sweden and the United States. The same thing is true of the known population growth of Austria, Belgium, Denmark, England and Wales, Hungary, Italy, Scotland, Serbia, Japan, Java, Philippine Islands, the world as a whole, and Baltimore city.*
[* Ibid., pp. 13-17.]
The similarities Pearl mentions show up graphically in his charts for Sweden, the United States, and France, reproduced in Figs. 5, 6, and 7.
Now comes a vital and significantly useful fact. When a consistent pattern of growth exists, we have sound grounds for making predictions. However qualified those predictions may be, they have the probabilities on their side. Thus, when we have enough census records — as for the United States — to establish a number of points on the chart of its population growth, we may observe the pattern of growth that exists; and knowing what the pattern is, we may project it into the future for purposes of prediction.
Fig. 6. Growth of the Population of the United States (After Pearl)
We may similarly project it into the past. France, for example, is an old nation; but we lack reliable census data for France before 1800. Data available since then, however, are sufficient to create the segment of a curve which may be projected backward as well as forward. The curve for France’s present cycle of growth had practically reached its upper limit in prewar days, and suggested decline. The period of time required by a given nation to go through the familiar pattern of growth varies greatly. With France, the period seems to have been something over four centuries for its current cycle. But records for Algeria convinced Pearl that this one small country had lived through almost a complete cycle of growth, from youth to maturity, in less than a hundred years — that cycle com prising the period of open French control following conquest, which seems to have been completed around 1850 (see Fig. 8).
Fig. 7. Growth of the Population of France (After Pearl)
This leads to another striking observation. Algeria was an old country, with an indigenous population, before it was brought under French domination. The introduction of French control apparently launched a new cycle in the nation’s life. Alterations in the environment were sufficiently radical to permit a new cycle of population growth to superimpose itself on whatever old one had existed — one for which we have no census records. When the new trend began, it followed exactly the pattern of expansion we are now familiar with in other countries.
We may thus reach an interesting observation. New cycles of growth may be superimposed upon old ones. We cannot predict when this will happen. Nor can we, as regards humanity, predict the conditions that permit it to happen. But a new cycle can appear when some fundamental change occurs.
If we put our colony of Drosophila into a larger bottle, with greater food supplies, a new cycle of growth would begin, but with a pattern quite similar in shape to the old. Similarly, a nation can apparently effect, through a reorganization of its resources, a change in environmental essentials which accomplishes much the same end. It seems to be established, for instance, that the introduction of an industrial economy permits a new rate of population growth substantially in excess of that which was sustained by the community when it was dominantly agricultural.
Fig. 8. Growth of the Indigenous Native Population of Algeria (After Pearl)
The world has striking evidence of this in the case of Russia, which following 1917-1918 entered into a new growth cycle. In terms of this new cycle, Russia stands today as the youngest of the great nations in the world. The United States is comparatively an old nation, in the sense of the dynamic forces that are reflected in a rate of growth, biologically and industrially.
Fig. 9. Growth of the Population of Germany
This chart (after Pearl) makes apparent two cycles of growth which have overlapped during the period of census history.
Pearl was convinced that a similar new cycle was once evidenced in Germany, where census records go back far enough to permit him to find a modern cycle of growth superimposed on an old one In the first half of the nineteenth century, Germany’s population was reaching the upper level of growth in a cycle that had prevailed since the 1600's. For years the nation had been predominantly agricultural. The abortive democratic revolution of 1848 was coincident with the beginning of a new industrialization, conducted under Prussian leadership, and new political forms. In the twenty years that followed 1850, this industrialization reached a development that permitted the swift defeat of France in 1870. The further unification of Germany that Bismarck then imposed seems merely to have added impetus to the new growth in strength already then established. These events were almost immediately reflected in a rapid increase in the population’s rate of growth. The upsurge was clearly in evidence by 1870, and subsequent census figures demonstrated that a new cycle of growth had begun, as shown in Fig. 9.Germany’s new pattern of growth, following 1850, demonstrates an interesting and perhaps significant point, when her population chart is compared with those for England, France, and the United States: Germany in 1914 was in one sense the youngest of these four industrialized nations. This may help account for the extraordinary vitality evidenced by the German people in their rapid rise from their 1918 defeat — one which hardly disturbed their social integration. What it may mean hereafter is wholly problematical, since today’s Germans, living in the world’s greatest mass of ruins, seem only individual remnants or survivors of a population that no longer is a united nation.
For our own purposes here, the past pattern of Germany’s population growth is worth noting only because it leads to a conclusion which Pearl phrases succinctly:
When human social evolution does manage to put a kink in the curve of population growth, it has not done it by altering any biological law. It merely shifts, by a greater or smaller amount, the absolute base from which the law operates. Then the process goes on as before.*
[* Ibid. p. 20]
It is possible to draw another conclusion from which Pearl abstains, but
