WORLD POPULATION GROWTH

The human race, even if its destiny appears unique, is part of the general evolution of the animal kingdom. But it is in the vanguard of that evolution since it is able to gain increasing mastery over its environment. Humanity's dominance of the planet and its exploitation of the Earth's resources have been accompanied by major increases in the size of human populations.

Prehistoric Beginnings

Possibly as long as 3 million years ago, Homo habilis emerged in East Africa. Its distinguishing characteristics were that it made, and more or less systematically used, tools of wood or flint stone, and that it exhibited a novel, more advanced type of social behavior: It consumed food not where it was obtained but at the group's campsites. The territory occupied by these early humans covered some 4 million square kilometers (about 1.5 millon square miles) of wooded savanna-land between today's Ethiopia and Zimbabwe. According to an estimate by János Nemeskéri, there may have been a population as great as 100,000, already exhibiting subgroups with distinct physical features.

From then onward, human genetic change has been very rapid: Most notably brain size, which at the start was less than 500 grams, increased by more than 1 kilogram in less than 3 million years. In successive stages of evolution, the great selective advantage that resulted gave humans the ability to eliminate their nearest competitors. Homo habilis thus yielded its place to Homo ergaster, which, having quadrupled the territory it occupied in Africa, spread to Europe and to southern Asia, taking on the closely similar form of Homo erectus.

In the twenty-first century, numerous methods are available for making estimates about prehistoric populations. The most commonly used method assigns to a given territory the population density among peoples with similar culture and who are living under similar climatic conditions, observed in some recent period. The resulting estimates indicate small populations, despite technical advances such as the domestication of fire. The extent of the territory occupied and variations in climate thus appear more influential than technical progress. The population size of Homo erectus over the entire earth may have varied between 500,000 and 700,000.

Later, three branches of humanity emerged: Homo sapiens in Africa and south Asia, Homoneanderthalensis (Neanderthal man) in Europe, and Java man in Indonesia. Hypothetically, the maximum population of Homo sapiens was about 800,000 in the Afro-Asian territory, while the corresponding numbers for Neanderthal man and Java man may have been 250,000 and 100,000.

From around the onset of the last Ice Age, some 70,000 years ago, Homo sapiens were ascendant and in the subsequent millennia spread over continental territories theretofore unoccupied by man: Australia, Siberia, and eventually the Americas. (Up to about 15,000 years ago, large parts of North America and Europe were under ice cover.) The world population may have reached 1.5 million during this period, most of it in Africa and Asia. Technical progress became the main driving force of demographic expansion.

Settlement of North Africa came relatively late. Taking advantage of the narrowness of the straights between Sicily and Tunisia, Europeans crossed over to Africa in two waves–around 20000 b.c.e., and around 12000 b.c.e.–thus peopling the whole of North Africa from the Canary Islands to Egypt.

In Europe, population size may have attained 200,000 persons in the period from 10000 to 8700b.c.e. Then there was a sudden warming of the climate, coinciding with a brutal end to the flourishing Paleolithic cultures. At the beginning of the Mesolithic period that followed, population size diminished, but subsequently the peopling of Northern Europe, earlier under ice cover, renewed demographic growth. Toward 7000 b.c.e., population size in Europe as a whole may have approached 400,000.

Late Prehistoric Populations

About that time, a small sedentary population, engaged in agriculture and animal husbandry, established the first known Neolithic village, near twenty-first-century Saloniki in Greece. From this region two streams originated, together forming the population of Neolithic Europe: one, a maritime group, occupying the coastal regions all the way to Britain; the other a terrestrial group, occupying the inland. By 4000 b.c.e., almost all Europe was Neolithic, with a population of some 2 million, and growing. That population peaked around 2000 b.c.e. at some 23 million, followed by a sharp drop early in the Bronze Age, which was then beginning.

This Neolithic culture was born in the Near East. Its main constituting elements–the hoe, animal husbandry, pottery, and maritime navigation–make their appearance in the period from 10000 to 8000 b.c.e. The region's population increased over this period from about 200,000 to around 5 million, and reached some 10 million by 2000 b.c.e. From its core, the culture spread to Mesopotamia, Egypt, the Caucasus, the Persian Highland, the Punjab, Nubia, Ethiopia, and Yemen.

The Asian subcontinent–present-day Pakistan, India, Bangladesh, and Sri Lanka–had a larger population: perhaps about 600,000 people by 4000 b.c.e., 3 million by 3000 b.c.e., and a peak of some 20 to 25 million by 2000 b.c.e.

In East Asia, beginning around 8000 b.c.e., a Neolithic culture arose in the lowlands of the Hoang-Ho (Yellow River), covering a region of some 600,000 square kilometers, and spread rapidly to the East and later to the South. The population may have reached 800,000 by 4000 b.c.e., 3 or 4 million by 3000 b.c.e., and 20 million by 2000 b.c.e.

Other Neolithic populations appeared somewhat later in Mexico and the Andean Highlands. Based on the examination of pottery evidence, Neolithic-type cultures also arose in Japan from around 12000 b.c.e. and in the African Sahel from around 8500 b.c.e.

From 6000 b.c.e. to 4000 b.c.e., the world's population may have risen from 6 or 7 million to near 30 million; 2,000 years later, as the plough was replacing the hoe, it may have reached 100 million.

Population Growth Since Antiquity

If chronologically widely-spaced estimates are made, a curve connecting the plotted points of these estimates gives the impression of smooth exponential growth from the distant past to the present. Colin McEvedy and Richard Jones, starting from 400 b.c.e., presented this type of curve with some light fluctuations; but the dominant impression conveyed is virtually uninterrupted exponential growth.

Yet the best known populations since Antiquity–the populations of Europe, China, the Near East, and Japan, which together comprise more than half of all humanity–exhibited marked fluctuations. Compartmentalization of the overall total into broad cultural subgroups reveals these fluctuations (see Table 1). The estimates shown in the table are not precise; even data from twentieth-century census counts from developed countries cannot be claimed to be such. But various checks on the estimates for early dates tend to support the numbers, and as to recent census data, the typical error in census counts has been demonstrated to be about 1 to 2 percent in developed countries and 5 to 30 or even 40 percent in certain developing countries up to the middle of the twentieth century.

Recent studies provide population estimates since Antiquity for various Near Eastern populations–notably for Egypt and Palestine–but interpretation of the underlying data from the ancient, medieval, and Ottoman periods is problematic.

China has a remarkable series of population counts starting at the beginning of the era shown in the table. Use of that data requires great care, but the broad lines of population growth have been established.

For Japan, even if the early estimates are uncertain, the population numbers are well known starting with the early seventeenth century, thanks to the use of temple-registers in which all persons residing in a given village or town district were required to be recorded.

For Europe, documents from Antiquity relating to population are rare. For the medieval period, fiscal

TABLE 1

records provide an important basis for estimates. The main difficulty is to correctly interpret the concept of the hearth: The term originally corresponded to the household, but its meaning shifted starting with the late fourteenth century. Later, for the sixteenth and seventeenth centuries (and for the eighteenth century in Eastern Orthodox countries), the use of parish registers allow accurate estimates of population characteristics and population change.

For the Indian subcontinent, the estimates shown follow those by Ajit Das Gupta, starting with the estimate of 150 million for the year 1600. That number is broadly confirmed by Shireen Moosvi who gives an estimate of 145 million for the year 1595. For earlier periods, the interval estimates provided by John Durand are used; these show peaks of 50 to 60 million persons for the three most prosperous periods: those of the Mauryan Empire (321–185 b.c.e.), the Gupta Empire (320–470 c.e.), and during the rule of Harsha (612–627 c.e.).

For the Americas and for Australia, despite occasional claims on the matter, there is no plausible evidence to support any substantial population densities for the early periods.

For Africa, existing records yield population estimates for the northern part of the continent, but very little is known prior to 1800 for Africa south of the Sahara. The slave trade (involving some 10 million persons taken to the Americas and some 4 million or more to Muslim lands) very likely removed the larger part of natural increase over the period it existed, causing long-term stagnation of population size. Censuses from the nineteenth century and for the early part of the twentieth century almost certainly substantially underreported population sizes. The figures in Table 1 take this into account.

Estimates for the world population as a whole can be taken as accurate within plus or minus 5 percent since 1900, within 7 to 8 percent between 1700 and 1900, within about 10 percent between 1500 and 1700, and perhaps within 15 percent before 1500.

Population Surges and Fallbacks

Three major technological revolutions resulted in three great population surges in the course of human history:

• acquisition of clothing and hunting and fishing tools in the Upper Paleolithic period (c. 30000–10000 b.c.e.);
• sedentarization and the introduction of agriculture, animal husbandry, and maritime navigation in the Neolithic period (c. 8000–5000 b.c.e.);
• the industrial revolution, which began in the eighteenth century and will conclude in the twenty-first century, as the post-industrial era takes over.

The amplitude of recurrent falls in population due to climate change in prehistoric times, and due to disease, war, and famines starting with the Neolithic period, may be put at between 10 and 20 percent.

Extrapolations of population size based on historical estimates spanning only a few centuries have been demonstrated to be worthless. Based on the population growth rate of the fourth and third centuries b.c.e., an extrapolation would yield a year 2000 population of more than 20 billion. Extrapolation of the growth rate for the third and fourth centuries c.e. would yield a population in 2000 of only 35 million.

Changing Behaviors

By and large, in prehistoric populations the level of mortality allowed a modest measure of natural growth for several years on end. Typically, a bad year removed that gain in numbers. Starting with the Neolithic era, the level of mortality decreased slightly and the expectation of life at birth reached about 25 years. In Europe, these underlying health conditions persisted until the sixteenth century when a fall in mortality commenced, gathering speed up to and into the twentieth century. In Western Europe, in around 1800, the expectation of life at birth was about 35 years; by 1900 it was about 50 years; and by 2000, 75 years (with a six to eight year difference favoring the female population), while in Eastern Europe it was about 40 years in 1900 and 65 years in 2000. Outside Europe, only the countries of European settlement (North America, Australia, and New Zealand) and Japan had a similar mortality record. Finally, at the middle of the twentieth century, the achievements of modern medicine caused a spectacular rise in life expectancy globally.

It seems that up to the Mesolithic era, the causes of death due to climatic factors (the scarcity of edible plants and wild game) played an important role in the regulation of population. In the Mesolithic era, production and, to a certain degree, storage of harvests and of domestic animals greatly lowered vulnerability to climatic risk, and the population increased rapidly. But above a certain population density, epidemic illnesses, previously rare, multiplied and played an increasingly important role in population regulation. From sixteenth-century Europe, there begins to be some success in the struggle against these epidemics. The plague was almost eliminated in the course of the seventeenth century; smallpox was under attack in the eighteenth century (and nearly eliminated in the nineteenth century); and in the twentieth century, all infectious diseases, which formed the second-most common cause of death up to the middle of the nineteenth century, were attacked and in most cases brought under control.

Fertility, with an average number of children per woman of around 6 or 7, showed little evidence of being voluntarily limited until well into the seventeenth century. Contraceptive practice was largely nonexistent. Voluntary limitation of births among the general populace can be traced back to the early eighteenth century in three French regions–Champagne, Normandy, and Aquitania–commencing even before any decline of mortality began. In France at large, from an average level of 6 children per woman at the beginning of the eighteenth century, fertility fell to 3 children per woman by 1800. From then on, the absolute number of births in France stagnated, while it doubled in all the other countries of Europe. Only Japan had a similar fertility experience. Elsewhere in Western Europe, fertility began falling only in the last quarter of the nineteenth century, and in Eastern Europe in the first decade of the twentieth century, long after mortality had shown a decrease. Among European colonists in America, fertility was very high in the eighteenth century, with an average of about 7 children per woman. In the United States, however, a decline of fertility started in the late eighteenth century and continued up to the second third of the twentieth century. A similar process began in the second half of the twentieth century in much of Latin America, then in East Asia and, more slowly, in India, and finally in most Muslim countries (with the exception of Palestine) in the 1980s and, more hesitantly, also in Africa south of the Sahara.

Structural Changes

The age distribution of the world population remained very young for a long period, reflecting both high fertility and high mortality. Thus, the effects of dramatic demographic shocks were rapidly erased from the age pyramid. Starting around 1800, however, both France and Japan showed an increase in the proportion of older persons. In effect, the decrease of fertility shrinks the proportion of persons who are young and increases the share of the elderly. The decline of mortality, especially when it improves infant survival, also contributes to a rejuvenation of the population age structure.

Once voluntary limitation of fertility appears, changes in the age distribution also become irregular. Twentieth-century age pyramids in Europe show marked perturbations resulting from fluctuations in the annual number of births–with differences between peaks and troughs that may amount to as much as 50 percent.

Populations of European origin in America and Oceania show more regular changes in the number of births, and substantial immigration also contributes to smoothing the jaggedness of the age pyramids.

In the developing world, from about the middle of the twentieth century, medical advances lowered mortality and increased fertility by improving health and extending the number of years spent in the married state. This resulted in exceptionally rapid population growth, further amplified by a rejuvenated age distribution. Coping with such growth without impoverishment requires heavy economic investment, which many of the countries affected were unable to afford and that consequently experienced serious economic difficulties. Economic outcomes also varied with ownership of resources and other assets and with political conditions–with some countries losing their elite class and their wealth through wars and other calamities.

The decline of fertility that began in almost all developing countries between 1970 and 1990 halted the trend toward younger age distributions. But, by 2000, the phenomenon of population aging was still in a very early phase.

Over the first half of the twenty-first century the global population is projected to increase from 6 billion to around 9 billion. But by the end of this period the growth rate is likely to be much diminished. The very youthfulness of the twenty-first century developing world favors rapid generational change, including change of ideas and attitudes. If so, the future pace of decline in fertility may turn out to be more rapid than is now anticipated.

See also: Archaeogenetics; Climate Change and Population: History; Epidemics; Health Transition; Mortality Decline; Peopling of the Continents; Prehistoric Populations; Projections and Forecasts, Population.

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Jean-NoËl Biraben