On October 31, 2011, the U.N. identified a newborn in the Philippines as the 7 billionth person on the planet. Danica May Camacho was born in Manila two minutes before midnight. Her father is a driver who struggles to support his family in one of the biggest and most densely populated cities in the world. Danica was born a month premature—if she'd been born a month later, she would have entered a world with approximately 6.5 million more people in it.

Identifying Danica was a largely symbolic gesture on the part of the U.N. to bring attention to the rate of population growth and concerns about limited resources. Demographers debate when exactly the world population reached (or will reach) 7 billion, though most agree that it's within a year of October 2011.

The last century has been one of unprecedented population growth; the population has increased by 5 billion. In 1798, when there were only 1 billion people, Thomas Malthus theorized that because human population grows exponentially and agricultural production increases much more slowly, overpopulation would eventually result in a "war of extermination, sickly seasons, epidemics, pestilence, and plague."

How did our population grow so quickly? Qian Cai, a demographer at UVA's Weldon Cooper Center, explains that the last century has seen extraordinary growth as part of "demographic transition." It may sound like a dry, academic term, but it's key to explaining the population boom. And it just might show us how we could avoid a Malthusian nightmare.

Demographic transition refers to a four-stage process that happens to populations as nations develop from pre-industrial to industrialized economies. The term was coined by American demographer Warren Thompson in 1929. He observed that it had occurred in industrialized nations beginning in the 18th century and that developing nations seemed to be in the early stages of transition.

We were in the first stage for most of human history; birthrates were very high but so were death rates, so population was virtually stable. "Then as new agricultural practices began to produce more food and medicine began preventing premature death, death rates declined while birthrates continued to be high," says Cai. "Thus population experienced a period of fast growth in the 20th century." This is the second stage, and it is how we added 5 billion people to the population in just a century.

But what happens then? Does our population keep growing at the same rate forever? Turns out, it doesn't. In the third stage, birthrates fall. Ever notice that most people you know have fewer siblings than aunts and uncles? In industrialized nations, like China and the U.S., that tends to be true of most people.

"When you look at different parts of the world today, you see nations in different stages of demographic transition," says Cai. "Some places are growing quickly, while others are in decline."

The fourth stage of demographic transition is decline. Births fall below 2.1 children per woman, which is the replacement fertility rate required to keep a population stable. Countries such as Japan and Russia are currently in this stage.

Demographic transition isn't a perfect model; some social scientists criticize it for attributing too much to economics and ignoring cultural and political factors. But it's a helpful model when considering why there are 7 billion of us and what might happen next.

The United States: Aging and Continued Growth

The population of the U.S. tripled in the 20th century and currently stands at approximately 313 million. The U.S. is the third most populous country in the world and has the largest economy. Over the last two centuries, the population has grown due to both birthrates and immigration.

Cai says one of the most significant trends in the U.S. population is aging. "Low fertility and greater longevity result in population aging, meaning the proportion of older people in the population continues to increase. This is a global trend, and certainly a trend for the U.S., and for Virginia." Currently about 13 percent of Virginia's population is over the age of 65. By 2030, one in every five Virginians is expected to be over age 65. "An economy needs people of working age to support the young and the old," she says. "When you don't have sufficient workers in the labor market, economic growth suffers."

The U.S. Census Bureau projects that by 2050 there will be 439 million Americans. "Compared to other industrialized nations, the U.S. is still growing quickly," says Len Schoppa, a professor in UVA's department of politics. "Japan, South Korea, most countries in Europe have much lower growth rates, if not decline." Schoppa suggests that continued growth in America may be due to cultural factors, including a relatively religious population—"Be fruitful and multiply"—and an economy where mothers can easily re-enter the workforce.

South America: The Haves and the Have-Nots

Brazil and Bolivia share a long border, yet the two nations are in different stages of demographic transition. There is disparity in growth between rich and poor countries in South America, much like the rest of the world.

Brazil is the largest nation in South America and the second richest. In 1960, the average Brazilian woman had 6.2 children, but by 2011 that number had decreased to 2.8. Like the U.S., Brazil's population is largely made of up immigrants and the descendants of immigrants; Brazil receives the third largest number of immigrants in the Western Hemisphere after the U.S. and Argentina.

In contrast, Bolivia is one of the least economically developed nations in the Western Hemisphere. The fertility rate is higher, three children per woman, and the population is younger, with a median age of 22. The median age in Brazil is 30 and the median age in the U.S. is 37 years old. Many Bolivians emigrate to find economic opportunity in countries like Brazil. Despite poverty and lack of education in Bolivia, the country has already seen a decline in fertility between 25 and 40 percent from its pretransitional numbers.

Hernan Moscoso Boedo, a professor in UVA's department of economics, explains the initial drop in the fertility rate. "It makes sense for subsistence farmers to have many children," he says "On the farm, a child is also an economic input, relatively cheap labor. Also, a high fertility rate counteracts a high infant mortality rate. Without a social security net, you need them to take care of you when you are old. But as the economy develops, and children's labor loses value, there is less incentive to have as many of them." Moscoso Boedo says that in an industrialized economy, the economic incentives for having children change in nature. "You have them because you want to spend time with them and enjoy that time," he says. "It's quality over quantity, so most people have fewer children."

Africa: The Boom That Arrived Late

Africa is the second biggest continent, but in 1950 it held only about 9 percent of the world's population. U.N. projections at the time suggested that Africa would grow quickly because the benefits of improved medicine and agriculture would bring down the death rate. But that change didn't come when it was expected. Birthrates remain high, as does infant mortality; in many sub-Saharan countries 40 to 50 percent of the population is younger than 15 years old. Death rates also remain high, and life expectancy remains low.

"The problems related to the death rate are a function of the AIDS-HIV crisis as well as the deterioration of the health system in many African countries. Expenditures on health have stagnated and the old, inadequate public system has deteriorated as budgets have been cut and the state emasculated," says Robert Fatton, a professor in UVA's department of politics. In the late 1980s, life expectancy in Botswana and Zimbabwe was between 55 and 60 years of age. By the early 2000s, it dropped below 40 in both countries.

Fatton reiterates Moscoso Boedo's point about the relationship between poverty and large families. He adds, "Women's poverty and lack of education as well as patriarchal forms of power contribute to high rates of birth even when structures of family planning exist."

Much of Africa is in an early stage of its demographic transition; as death rates begin to fall, birth rates likely will remain high for a while and the population will boom. Most of the world entered this stage during the second half of the 20th century, which caused the global population explosion. At present, Africa constitutes about 15 percent of the world population; by 2050 the continent will likely be home to 22 percent.

Asia: The Biggest

Six out of 10 of the most populous nations in the world are in Asia. In 1950, China had a population of 563 million. By 2011 it had grown to 1.33 billion. In the same year, India was home to 1.19 billion.

"The challenges posed by large populations are many," says John Echeverri-Gent, associate professor in UVA's department of politics. "They strain resources and infrastructure. They tax the environment. Countries want to invest in their human capital, but in places like India and, to greater extent, Pakistan, that is extremely difficult."

Indeed, Echeverri-Gent points out that extreme poverty, unstable governments or civil strife might impede demographic transition. Countries like Pakistan, the Palestinian Territories, Yemen and Afghanistan, where development is delayed by political problems, still have very high birth and death rates.

China has made efforts to control its own growth and imposed the one-child rule. In both India and China, where male children are prized, the numbers of female children declined as families selected for sex and invested a greater proportion of their resources in their male children. Echeverri-Gent notes that the natural sex ratio of children under 6 years of age is 952 girls per 1,000 boys. But in China and some of the states in northern India, the ratio has fallen to less than 850 girls per 1,000 boys meaning that there are millions of "missing girls," says Echeverri-Gent.

Birthrates are declining. In China, women have an average of 1.54 children. China, and countries such as Brazil and Thailand, passed through the demographic transition quickly because their economies and societies changed very quickly. China is considered to be at the same stage of demographic transition as the United States. In India, the birth rate has been falling since 1975 and women now average 2.63 children, which marks a more than 40 percent decrease in the fertility rate.

"India and China have also seen extraordinary economic growth," says Moscoso Boedo. "The increases in per capita wealth in India and China have pulled the world median income up significantly."

The most developed nations in Asia face population decline. "Fifty years ago, Japan, South Korea, Singapore and Hong Kong had high birthrates and growing populations," says Schoppa. "Now their populations are aging and their birthrates are below replacement level. In the next 40 years, the population of Japan will likely decrease by 30 million."

During the 2000s, the death rate in Japan—where people live longer than anywhere else—outstripped the birthrate. Fewer Japanese workers must provide for an increasing number of retired people. "Japan's already dealing with an aging population in a way that the U.S. will have to in a few years," says Schoppa.

Europe: Not as Big (Relatively) as It Used to Be

One hundred years ago, Europe was home to one quarter of the world population. The U.N. projects that, in 2050, Europe will account for only 7 percent. Despite low birthrates, many European countries like Ireland, Great Britain and Spain have modest growth rates. But some, such as Germany, Poland and Bulgaria, are declining. "The Industrial Revolution happened in Europe first and women joined the workforce in large numbers there first, so the demographic transition happened there first," says Schoppa. "Because they've had time to adjust to low birthrates, some governments have dealt with the possibility of decline by offering incentives for childbearing, such as tax advantages and free childcare."

Low birthrates and an aging population present their problems to European economies and political and social institutions. "Economies can shrink due to labor shortages and decrease in demand," says Cai.

"How do we pay for a good quality of life for everyone with fewer workers?" says Schoppa. To a certain extent, labor moves from country to country for better economic opportunities. "But there are barriers to the movement of labor," says Schoppa. "It's slow. People have to adapt to their new countries, sometimes there's cultural resistance to it, like in Japan."

"There is an impression that Southern Europe has higher birthrates than Northern Europe, but in fact the opposite is true," says Moscoso Boedo. In the United Kingdom, the historically lowest birthrate was 1.63 per woman in 2001, and now women have an average of 1.98 children. In Italy, the birthrate was at its lowest point in 1995, when it fell to 1.18 per woman. It has since risen to 1.41 per woman. "In Southern Europe, equality in the workplace did not translate to equality at home and women still bear more of the domestic responsibilities. It seems like that is not conducive to childbearing."

The population of Russia is shrinking. It peaked at 148.5 million in 1991, just before the Soviet Union was dismantled, but has declined since by about 5.5 million. "The dramatic decline of population in Russia can be attributed primarily to the collapse of the Soviet Union in 1991, although some of the trends … started earlier. The most striking feature for almost two decades after the Soviet collapse has been the sharp increase in the death rate, especially among men, which led to the unprecedented drop in life expectancy," says Katya Makarova, an associate professor in UVA's department of sociology.

The death rate in Russia had been slowly climbing since the 1960s. In 1992, it outpaced the birthrate and has been higher ever since. "Many factors have contributed to this: the collapse of the public health system, increase in alcoholism, drug abuse, suicide, tobacco use and cardiovascular disease as well as a surge in infectious diseases such as tuberculosis and HIV/AIDS," says Makarova. "Birthrates have also plummeted. This is caused by economic concerns, the sense of insecurity about jobs and income, and uncertainties about the future."

Russia had already completed its demographic transition by 1991; it serves as a counter example to nations where poverty and high birthrates are correlated.

The Earth at Night: This NASA photograph of the world at night shows where large industrialized populations live. Some places don’t emit much light despite large populations. North Korea for example, has an  estimated 22.5 million people but appears dark in this image.

There Are More Of Us Than Ever Before, but We Aren't Growing at the Same Rates as We Once Were

As the nations of the world complete their own demographic transitions, global growth rates will slow. "We are already slowing down on a global scale," says Moscoso Boedo. "And because economies and nations run on ideas, human ingenuity will help us with the challenges of a large population. We respond to changes in our environment and our circumstances."

Malthus feared that the human population would grow uncontrollably, which would result in disaster. But we might be in the midst of a process of adapting to the new circumstances of a bigger population and a more industrialized planet.

"Although extremes in either direction of population growth or decline would negatively impact how we live, there isn't implicit value to a bigger population or smaller one. In places in the world where we see them, each has its own benefits and challenges," says Cai.

Meanwhile, Danica May Camacho is 4 months old. She's been joined by 26 million new people since her birth. That's about the same number as live in the state of Texas. Or in Nepal. And together all 7 billion of us will determine what kind of world she grows up in.


The Scholar's Lab at the University of Virginia Library is a place where faculty, staff and students can explore digital resources, find expert help and collaborate on research projects. Need to map population growth across the globe? They can help. From their offices in Alderman Library, Chris Gist, Kelly Johnston and Eric Johnson find new and innovative ways to use digital technology to make better sense of the world.

The Weldon Cooper Center for Public Service Demographics & Workforce Group at UVA is a small but diverse team of research, policy and communications professionals who work on a wide range of projects in the public interest. Every year the center develops and releases the official population estimates for Virginia and its counties and cities. The estimates are used in funding formulas based on per capita allocations and in all manner of state agencies. The center is also directed by the General Assembly to develop annual estimates of the school-age population, and those estimates drive how much state funding local school divisions receive from a portion of the state sales tax.

The statistics used in this article were sourced from the United Nations and the CIA World Factbook unless otherwise noted.