Estimates of world population by their nature are an aspect of
modernity, possible only since the
Age of Discovery. Early estimates for the population of the world date to the 17th century:
William Petty, in 1682, estimated the world population at 320 million (current estimates ranging close to twice this number); by the late 18th century, estimates ranged close to one billion (consistent with current estimates). More refined estimates, broken down by continents, were published in the first half of the 19th century, at 600 million to 1 billion in the early 1800s and 800 million to 1 billion in the 1840s. It is difficult for estimates to be better than rough approximations, as even current population estimates are fraught with uncertainties from 3% to 5%. Agriculture provided a steady food supply that could be stored for a year or longer in order to minimize the risk of famine. Farm production could be expanded by systematic human exertion. The new technology of farming meant that the food supply was proportional to the number of workers who could plant and harvest the crops. Every new pair of hands meant more food for the community, so children were valued in agricultural societies. Later, additional workers found useful work in building irrigation canals and systems that provided a stable water supply for crops, especially in Egypt, Mesopotamia, India, China, Peru and Mexico. The population could now grow because new people paid their own way. (It would take many centuries before the arable land supply became a limiting factor.) However, death rates were high, especially for infants and children, so even with high birth rates growth was slow. The same amount of land could support either 1,000 hunters or 100,000 farmers, and it is easy to see which side ultimately would win a fight for the land. Farmers gathered in permanent villages, and through a process of warfare consolidated into much larger states, including those in China, India, Egypt and Mesopotamia. From 300 to 1400 AD large agricultural states also existed throughout the eastern United States, called the "
Hopewell tradition" and "
Mississippian cultures". They are most famous as
Mound Builders, but their culture collapsed (for unknown reasons) by 1500. The natives encountered by the English and French were nomadic hunters who supplemented their meat diet with cultivated vegetables.
Ancient and post-classical history . It shows exponential rise in world population that has taken place since the end of the seventeenth century. Estimates of the population of the world at the time agriculture emerged in around 10,000 BC have ranged between 1 million and 15 million. Even earlier, genetic evidence suggests humans may have gone through a population bottleneck of between 1,000 and 10,000 people about 70,000 BC, according to the now largely discredited
Toba catastrophe theory. By contrast, it is estimated that around 50–60 million people lived in the combined eastern and western
Roman Empire in the 4th century AD. The
Plague of Justinian caused Europe's population to drop by around 50% between the 6th and 8th centuries AD. The population of Europe was more than 70 million in 1340. From 1340 to 1400, the world's population fell from an estimated 443 million to 350–375 million, with the
Indian subcontinent suffering the most tremendous loss and Europe suffering the
Black Death pandemic; it took 200 years for European population figures to recover. The population of China decreased from 123 million in 1200 to 65 million in 1393, presumably from a combination of
Mongol invasions, famine, and plague. Starting in AD 2, the
Han dynasty of
ancient China kept consistent family registers to properly assess the poll taxes and labor service duties of each household. In that year, the population of
Western Han was recorded as 57,671,400 individuals in 12,366,470 households, decreasing to 47,566,772 individuals in 9,348,227 households by AD 146, towards the
end of the Han dynasty. England's population reached an estimated 5.6 million in 1650, up from an estimated 2.6 million in 1500. New crops that were brought to Asia and Europe from the Americas by Portuguese and Spanish colonists in the 16th century are believed to have contributed to population growth. Since their introduction to Africa by Portuguese traders in the 16th century, maize and
cassava have similarly replaced traditional African crops as the most important
staple food crops grown on the continent. The
pre-Columbian population of the Americas is uncertain; historian David Henige called it "the most unanswerable question in the world." By the end of the 20th century, scholarly consensus favored an estimate of roughly 55 million people, but numbers from various sources have ranged from 10 million to 100 million. Encounters between European explorers and populations in the rest of the world often introduced local
epidemics of extraordinary virulence. According to the most extreme scholarly claims, as many as 90% of the
Native American population of the
New World died of
Old World diseases such as
smallpox,
measles, and
influenza. Over the centuries, the Europeans had developed high degrees of immunity to these diseases, while the indigenous peoples had no such immunity.
Modern history During the European
Agricultural and
Industrial Revolutions, the
life expectancy of children increased dramatically. The percentage of the children born in London who
died before the age of five decreased from 74.5% in 1730–1749 to 31.8% in 1810–1829. Between 1700 and 1900, Europe's population increased from about 100 million to over 400 million. Altogether, the areas populated by people of European descent comprised 36% of the world's population in 1900. Population growth in the Western world became more rapid after the introduction of
vaccination and other improvements in medicine and
sanitation. Improved material conditions led to the population of Britain increasing from 10 million to 40 million in the 19th century. The population of the United Kingdom reached 60 million in 2006. The United States saw its population grow from around 5.3 million in 1800 to 106 million in 1920, exceeding 307 million in 2010.
20th century The first half of the 20th century in
Imperial Russia and the
Soviet Union was marked by a succession of major wars,
famines and other disasters which caused large-scale population losses (approximately 60 million excess deaths). After the collapse of the Soviet Union, Russia's population declined significantly – from 150 million in 1991 to 143 million in 2012 – but by 2013 this decline appeared to have halted. Many countries in the
developing world have experienced extremely rapid population growth since the early 20th century, due to economic development and improvements in public health. China's population rose from approximately 430 million in 1850 to 580 million in 1953, and now stands at over 1.3 billion. The population of the
Indian subcontinent, which was about 125 million in 1750, increased to 389 million in 1941; today, India, Pakistan and Bangladesh are collectively home to about billion people.
Java, an island in
Indonesia, had about 5 million inhabitants in 1815; it had a population of over 139 million in 2020. In just one hundred years, the population of Brazil decupled (x10), from about 17 million in 1900, or about 1% of the world population in that year, to about 176 million in 2000, or almost 3% of the global population in the very early 21st century. Mexico's population grew from 13.6 million in 1900 to about 112 million in 2010. Between the 1920s and 2000s, Kenya's population grew from 2.9 million to 37 million.
Milestones by the billions The UN estimated that the world population reached one billion for the first time in 1804. It was another 123 years before it reached two billion in 1927, but it took only 33 years to reach three billion in 1960. The United Nations, however, estimated that the world population reached seven billion in October 2011. According to the UN, the global population reached eight billion in November 2022, but because the growth rate is slowing, it will take another 15 years to reach around 9 billion by 2037 and 20 years to reach 10 billion by 2057. Alternative scenarios for 2050 range from a low of 7.4 billion to a high of more than 10.6 billion. Projected figures vary depending on underlying statistical assumptions and the variables used in projection calculations, especially the
fertility and
mortality variables. Long-range predictions to 2150 range from a population decline to 3.2 billion in the "low scenario", to "high scenarios" of 24.8 billion. There is no estimation for the exact day or month the world's population surpassed one or two billion. The points at which it reached three and four billion were not officially noted, but the International Database of the United States Census Bureau placed them in July 1959 and April 1974 respectively. The United Nations did determine, and commemorate, the "Day of 5 Billion" on 11 July 1987, and the "Day of 6 Billion" on 12 October 1999. The Population Division of the United Nations declared the "
Day of Seven Billion" to be 31 October 2011. The United Nations marked the birth of the
eight billionth person on 15 November 2022. ==Global demographics==