It took more than 50,000 Years for World Population to reach 1 billion People



“Demography is destiny” is an oft-cited phrase that suggests the size, growth, and structure of a nation’s population determines its long-term social, economic, and political fabric. The phrase highlights the role of demographics in shaping many complex challenges and opportunities societies face, including several pertinent to economic growth and development.

Nevertheless, it is an overstatement to say that demography determines all, as it downplays the fact that both demographic trajectories and their development implications are responsive to economic incentives; to policy and institutional reforms; and to changes in technology, cultural norms, and behavior.

The world is undergoing a major demographic upheaval with three key components: population growth, changes in fertility and mortality, and associated changes in population age structure.

Population growth

It took more than 50,000 years for world population to reach 1 billion people. Since 1960, we have added successive billions every one to two decades. The world population was 3 billion in 1960; it reached 6 billion around 2000, and the United Nations projects it will surpass 9 billion by 2037. The population growth rate has been slowing, however, from peak annual rates in excess of 2 percent in the late 1960s, to about 1 percent currently, to half that by 2050.

Although global income per capita more than doubled, life expectancy increased by 16 years, and primary school enrollment became nearly universal among children during 1960–2000, rapid population growth poses myriad challenges that are both privately and publicly daunting. These challenges include the need for more food, clothing, housing, education, and infrastructure; the absorption of sizable numbers into productive employment; and more strenuous environmental protection. Although the explosive nature of global population growth is abating in relative terms, decade-on-decade increases remain sizable and are taking place from ever more populated starting points.

Earlier concerns about a global population explosion have, to some extent, yielded to concerns about rapid population growth in particular countries and regions (see “Coming of Age” in this issue of F&D). Indeed, the overall slowdown in the rate of world population growth masks significant shifts in the distribution of world population by development status and geographic region.

Countries the United Nations classifies as less developed encompassed 68 percent of world population in 1950; today they represent 84 percent. That share will continue to rise, because virtually all of the nearly 2 billion net additions to world population projected over the next three decades will occur in less developed regions. This is a major concern, because less developed regions tend to be more fragile—politically, socially, economically, and ecologically—than their more developed counterparts.

With 1.44 billion people, China currently has the largest national population in the world, followed by India, with 1.38 billion. But by the end of this decade, India will be the most populous country, with a projected 1.50 billion people, compared with China’s peak population of 1.46 billion. Between 2020 and 2050, Nigeria (projected to overtake the United States to become the world’s third-most-populous nation) and Pakistan—already among the 10 most populous—will surge forward. Asia will continue to be home to a dominant but declining share of the world’s population (60 percent today and 54 percent in 2050).

Finally, notwithstanding continued global population growth, in 61 countries and territories that are currently home to 29 percent of the world’s people, population growth in 2020–50 is projected to be negative, with the sharpest decline (−23 percent) projected for Bulgaria (see “Eastern Europe’s Exodus” in this issue of F&D).

Mortality, fertility, and migration

Population size and growth reflect the underlying forces of mortality, fertility, and international migration. These forces vary considerably across countries and can help account for key differences in economic activity and performance, such as physical capital, labor, and human capital accumulation; economic well-being and growth; and poverty and inequality.

These forces generally respond to economic shocks; they may also respond to political developments such as the beginning and ending of wars and governance crises. In many developing economies, population growth has been associated with a phenomenon known as the “demographic transition”—the movement from high to low death rates followed by a corresponding movement in birth rates.

For most of human history, the average person lived about 30 years. But between 1950 and 2020, life expectancy increased from 46 to 73 years, and it is projected to increase by another four years by 2050. Moreover, by 2050, life expectancy is projected to exceed 80 years in at least 91 countries and territories that will then be home to 39 percent of the world’s population. Increased longevity is a colossal human achievement that reflects improvements in survival prospects throughout the life cycle, but especially among infants and children.

Cross-country convergence in life expectancy continues to be strong. For example, the life expectancy gap between Africa and North America was 32 years in 1950 and 24 years in 2000; it is 16 years today. Historic and anticipated reductions in cross-country health disparities reflect gains in income and nutrition among low- and middle-income countries, the diffusion of innovations in health technologies and institutions, and the distribution of international aid.

In the 1950s and 1960s, the average woman had roughly five children over the course of her childbearing years. Today, the average woman has somewhat fewer than 2.5 children. This presumably reflects the growing cost of child-rearing (including opportunity cost, as reflected mainly in women’s wages), increased access to effective contraception, and perhaps also growing income insecurity.

The social and economic implications of this fertility decline are hard to overstate. Among other things, lower fertility has helped relieve many women of the burden of childbearing and child-rearing. It has also contributed to the empowerment of women in their households, communities, and societies and has allowed them to participate more actively in paid labor markets. All these factors reinforce the preference for low fertility.

Between 1970 and 2020, the fertility rate declined in every country in the world. Fertility tended to decrease more in countries with high initial fertility, another facet of demographic convergence. Among geographic regions, Africa and Europe are currently homes to the highest (4.3) and lowest (1.6) fertility rates, respectively.

If the population’s age structure is sufficiently weighted toward those in prime childbearing years, even a fertility rate of 2.1 can translate into positive population growth in the short and medium term, because low fertility per woman is more than offset by the number of women having children. This feature of population dynamics is known as population momentum and helps explain (along with migration) why the populations of 69 countries and territories are currently growing even though their fertility rates are below 2.1.

Cross-country migration is also relevant to population growth. The effects are quite important in some countries, such as Guyana, Samoa, and Tonga, where net emigration in the past 30 years has been appreciable. Bahrain, Qatar, and the United Arab Emirates have had the highest rates of net immigration. Among the world’s 10 population super powers, migrants have the largest relative presence in the United States (15 percent in 2019). For most countries, though, international migration has not been a dominant demographic force, because more than 96 percent of the world’s population currently live in their countries of birth (see “Immigrant Swan Song” in this issue of F&D).



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