2.6 Population Growth — The Basic Idea

Population growth^?, also called population change, refers to the change in the number of inhabitants of a territory during a specific period of time. The change may be positive (when population rises) or negative (when it falls). It can be expressed either in absolute numbers (e.g. India's population grew by 18.15 crore between 2001 and 2011) or as a percentage (the same change, expressed as a growth rate of about 17.7 per cent over a decade). Population change is an important indicator of a region's economic development, social upliftment and historical-cultural background.

2.7 Components of Population Change

There are three components of population change — births, deaths and migration. Births and deaths together drive natural growth; migration adds the third dimension that converts natural growth into actual growth. Each component is measured by a standard rate.

A. Crude Birth Rate (CBR)

The Crude Birth Rate^? is expressed as the number of live births in a year per thousand of population. It is calculated as:

B. Crude Death Rate (CDR)

The death rate plays an active role in population change — population growth occurs not only by an increasing birth rate but also by a falling death rate. The Crude Death Rate^? is the simplest method of measuring mortality. CDR is expressed as the number of deaths in a particular year per thousand of population in a particular region.

By and large, mortality rates are affected by the region's demographic structure (age and sex composition), social advancement (literacy, sanitation, public health), and levels of economic development (income, nutrition, healthcare access).

C. Natural Growth Rate & Total Fertility Rate

The Natural Growth Rate^? is the difference between the Crude Birth Rate and the Crude Death Rate. If CBR is 22 per thousand and CDR is 8 per thousand, the natural growth rate is 14 per thousand, or 1.4 per cent per annum. Beyond the CBR, geographers also track the Total Fertility Rate^? — the average number of children a woman would have over her child-bearing years. A TFR of about 2.1 is the replacement level at which a population just replaces itself.

D. Migration — The Third Component

Apart from birth and death, there is another way by which the population size of a region changes — migration. When people move from one place to another, the place they move from is called the Place of Origin, and the place they move to is called the Place of Destination. The place of origin shows a decrease in population, while the population of the place of destination rises. Migration may be interpreted as a spontaneous effort to achieve a better balance between population and resources.

Migration may be permanent, temporary or seasonal, and may take place between rural and urban areas in any of the four directions: rural-to-rural, rural-to-urban, urban-to-urban or urban-to-rural. The same person, NCERT reminds us, is both an immigrant (when entering a new place) and an emigrant (when leaving the old one).

2.8 Trends in World Population Growth — A Long Story in Six Acts

The most striking single fact about world population is that human population increased more than ten times in the past 500 years. In the twentieth century alone, the population increased four times over. The story comes in clearly identifiable acts — pre-agriculture, agricultural revolution, industrial revolution, twentieth-century explosion, contemporary slowdown.

SVG Timeline — World Population Milestones

Figure 2.4: Schematic timeline of world population milestones. Notice how flat the curve is for tens of thousands of years, then how it suddenly bends upwards after 1800.

Three Engines of Growth — A Closer Look

Pre-agriculture (before c. 10,000 BCE): Humans lived as small bands of hunter-gatherers. Births balanced deaths almost exactly. Total world population is estimated at about 8 million — fewer people on the entire planet than live in modern Mumbai today.

The Agricultural Revolution^? (c. 8000 BCE onwards): The domestication of crops and animals provided a more reliable food supply, and settled villages began to form. Population climbed slowly but surely, reaching about 500 million by 1650.

The Industrial Revolution^? (mid-18th century onwards): Mechanised agriculture, improved sanitation, the germ theory of disease, vaccination, and rising real incomes drove the death rate down sharply. Births did not fall as fast, so populations exploded. The first billion was reached around 1820.

The 20th-century explosion: By 1930, world population reached 2 billion; 1960, 3 billion; 1975, 4 billion; 1987, 5 billion; 1999, 6 billion; 2011, 7 billion; 2022, 8 billion. The four-fold rise within just one century is unprecedented in human history.

Chart.js — World Population, 1650 to 2024

Figure 2.5: World population, 1650 to 2024 (millions). The line is nearly flat for 150 years and then rockets upward after 1900 — the so-called "hockey stick" of the demographic age.

2.9 Doubling Time — A Single Number That Tells the Story

The Doubling Time^? is the number of years a population would take to double at its current growth rate. There is a beautifully simple formula:

The historical pattern is stark. Before the year 1850, the world population doubled in about 200 years. By the early 20th century, the doubling time had shrunk to about 80 years. By the late 20th century, it had crashed to roughly 39 years. The doubling time is now lengthening again — current world growth is below 1% per year — meaning population will take more than 70 years to double next.

SVG — Doubling Time Visualisation

Figure 2.6: Doubling time shrank dramatically through the 20th century but is now rising again as growth slows below 1% per year.

2.10 The Spatial Pattern of Population Change

The most important rule of contemporary demography is that population growth varies sharply between developed and developing countries. Although growth rates have come down everywhere, the developing world is still adding the bulk of the planet's new people. NCERT identifies Africa as the continent with the highest growth rate — by a wide margin. South America and parts of Asia follow; Europe, North America and Oceania trail far behind, with several European countries showing actually negative natural growth.

Chart.js — Average Annual Growth Rate by Continent

Figure 2.7: Indicative recent annual growth rates by continent. Africa is the world's growth leader; Europe is contracting in many countries.

Chart.js — India vs China: A Population Photo-Finish

Figure 2.8: India and China together house roughly 36% of humanity. Around 2023 India is widely accepted to have overtaken China as the world's most populous country, even as China's population has begun to decline outright.

2.11 The Impact of Population Change

A small change in the rate of population growth can produce wildly different futures. A growth rate well above the world average warns of impending crisis — strains on schools, hospitals, water and food supplies, and growing unemployment. A negative growth rate is also a matter of concern in a different way — it indicates that the population is shrinking, which in turn means a shrinking labour force, ageing demography, and an increasing burden of pensions and elder-care on a shrinking working population.