# How the World’s Population Grew

> In 1960 Heinz von Foerster and two colleagues fitted a curve to two thousand years of population estimates in the journal Science and found it reached infinity on Friday 13 November 2026. This film explains how populations grow: Malthus's geometric and arithmetic ratios, exponential growth and doubling time, why the billions arrived faster and faster, the demographic transition that bent the curve, population pyramids, the United Nations' projection of a peak in the 2080s, and how Thailand went from six children per woman to about one. Run the doomsday clock, step through the transition, add the billions and reshape the pyramid.

Interactive film: https://www.planetpast.com/stories/how-world-population-grew/  
Publisher: PlanetPast (https://www.planetpast.com/) · d => T('readPublished', l, { d: dateIn(d, l) }) 2026-10-19 · Society, Math

## Prologue

### The doomsday curve
*A prediction from 1960*

A formula that sent humanity to infinity.

In November 1960, the journal Science published a paper with an alarming title: Doomsday, Friday, the thirteenth of November, A.D. 2026. The date it named was this autumn. Its three authors, led by the physicist Heinz von Foerster, had not predicted an asteroid or a war. They had fitted a curve to two thousand years of world population, and the curve shot to infinity. We are still here, more than eight billion of us. So what did the curve get right, what did it miss, and how does a population really grow?

![Five pages, 1291 to 1295, by von Foerster and two colleagues at the University of Illinois, Patricia Mora and Lawrence Amiot. AI-generated still.](https://assets.planetpast.com/a/97/979548c49d5f12fb.jpg)

- **24**: estimates of world population
- **± 5.5 years**: uncertainty on the doomsday date

- **8.2 billion**: in 2024, United Nations
- **≈ 3 billion**: when the paper appeared

Prologue · The news

#### A date on the calendar

Heinz von Foerster, Patricia M. Mora and Lawrence W. Amiot, “Doomsday: Friday, 13 November, A.D. 2026”, Science 132, 1291–1295 (4 November 1960). Popular Science and The New Daily revisited it in October 2026 as the date approached.

The world reached about 3 billion people in 1960 (UN estimate) and 8.2 billion in 2024 (UN World Population Prospects 2024). How to use: pick a chapter or press ← →; drag to rotate. Most steps have buttons.

The 3D charts are drawn from the numbers in the sources; the pyramids are schematic shapes, not census data.

Sources: [von Foerster, Mora & Amiot: Doomsday: Friday, 13 November, A.D. 2026. Science 132 (3436), 1291–1295, 4 Nov 1960 (PDF)](https://mozart.bioinfo.rpi.edu/bystrc/courses/biol4961/Doomsday.pdf); [Popular Science: In 1960, scientists predicted the world would end on November 13, 2026 (13 Oct 2026)](https://www.popsci.com/science/world-end-overpopulation-doomsday-november-2026/); [The New Daily: November 2026 doomsday prediction (13 Oct 2026)](https://www.thenewdaily.com.au/life/science/2026/10/13/november-2026-doomsday-prediction); [United Nations: UN projects world population to peak within this century (World Population Prospects 2024, July 2024)](https://www.un.org/sustainabledevelopment/blog/2024/07/press-release-wpp2024/)

## Chapter I · The doomsday equation

### A formula with a wall
*Chapter I · The doomsday equation*

Divide by a number that shrinks to zero.

Their formula is short. World population, N, equals a constant divided by the number of years left until one particular date. Halve the years left, and the population doubles. As the calendar approaches that year, the gap on the bottom shrinks toward zero, and the number on top grows without limit. The best fit put that date at 2026 point eight seven, give or take five and a half years. The authors put its central day, Friday the thirteenth of November, in their title. Press Run the clock to watch the curve race upward, and compare it with the real head counts.

$$N(t) = \dfrac{K}{(U - t)^{k}}$$
- $K$: 1.79 × 10¹¹ (fitted constant)
- $U$: A.D. 2026.87, “doomsday”
- $k$: 0.990 ± 0.009, so almost exactly 1
- $t$: the year

The paper called U − t “dooms-time”.

- 1960, formula: ≈ 2.8
- 1960, UN estimate: ≈ 3.0
- 2024, formula: ≈ 63
- 2024, UN estimate: 8.2

- **≈ 6.9 billion**: for the year 2000
- **≈ 26.6 billion**: for the year 2020

Chapter I · The doomsday equation

#### The fitted curve

von Foerster, Mora and Amiot fitted N = K/(U − t)^k to 24 estimates of world population from the time of Christ to the 1950s, by least squares: K = 1.79 × 10¹¹, k = 0.990 ± 0.009, U = A.D. 2026.87 ± 5.50. As t approaches U, N goes to infinity.

Values in the chart for 1960 and 2024 are computed from those constants (N(1960) ≈ 2.8 billion, N(2024) ≈ 63 billion). Real counts: about 3 billion in 1960 and 8.2 billion in 2024 (UN).

Sources: [von Foerster, Mora & Amiot: Doomsday: Friday, 13 November, A.D. 2026. Science 132 (3436), 1291–1295, 4 Nov 1960 (PDF)](https://mozart.bioinfo.rpi.edu/bystrc/courses/biol4961/Doomsday.pdf); [Wikipedia: World population milestones (UN estimates)](https://en.wikipedia.org/wiki/World_population_milestones); [United Nations: UN projects world population to peak within this century (World Population Prospects 2024, July 2024)](https://www.un.org/sustainabledevelopment/blog/2024/07/press-release-wpp2024/)

### Why it seemed to fit
*Chapter I · The doomsday equation*

The more people, the faster the growth.

The idea behind it was daring. In most growing things, each member adds offspring at a steady rate, so the total grows exponentially, by the same percentage every year. Von Foerster argued that people are not like other living things: the more of us there are, the more we cooperate and share what we learn, so the growth rate itself should rise as the population rises. Mathematicians call that hyperbolic growth. And for two thousand years, it looked right. Until about 1700, the world grew by roughly four hundredths of one percent a year. By 1963, growth had reached two point three percent a year, the fastest ever.

- exponential: the yearly percentage stays fixed; it never reaches infinity
- hyperbolic: the percentage grows with the population; it hits a wall at a finite date

![Fitting by least squares means choosing the curve with the smallest total error; across the 24 estimates it was off by about 7 percent. AI-generated still.](https://assets.planetpast.com/a/a5/a5ba4d9c1ec26764.jpg)

- average, 10,000 BC–1700: 0.04%
- peak, 1963: 2.3%
- recent: 0.9%

- **≈ 57 ×**: faster yearly growth: 2.3 ÷ 0.04

Chapter I · The doomsday equation

#### Exponential and hyperbolic

The paper starts from a model with constant productivity per person, which gives exponential growth, then lets productivity rise with population as a power law, because people who communicate and form coalitions may gain as they grow. Integrated, this gives a finite-time blow-up. The fit to 24 estimates had a root-mean-square deviation of about 7 percent.

Our World in Data: average growth from 10,000 BC to 1700 was about 0.04 percent a year; the peak was 2.3 percent in 1963; recent growth is about 0.9 percent a year.

Sources: [von Foerster, Mora & Amiot: Doomsday: Friday, 13 November, A.D. 2026. Science 132 (3436), 1291–1295, 4 Nov 1960 (PDF)](https://mozart.bioinfo.rpi.edu/bystrc/courses/biol4961/Doomsday.pdf); [Our World in Data: Population growth](https://ourworldindata.org/population-growth); [Our World in Data: World population growth, past and future](https://archive.ourworldindata.org/20251125-173858/world-population-growth-past-future.html)

## Chapter II · How populations grow

### Malthus’s two ratios
*Chapter II · How populations grow*

People multiply; fields only add.

The fear itself was much older. In 1798, the English clergyman Thomas Malthus published An Essay on the Principle of Population. He wrote that population, when unchecked, increases in a geometrical ratio: one, two, four, eight, sixteen. Food, he said, grows only in an arithmetical ratio: one, two, three, four, five. Press Next generation and watch the gap open. Malthus argued that something must always hold population back to what the land can feed.

![Harvests still depended on horses, ploughs and the weather. AI-generated still.](https://assets.planetpast.com/a/ef/ef30ffea3fc38ead.jpg)

- people: 1, 2, 4 … 256: 256
- food: 1, 2, 3 … 9: 9

> … the constant operation of the strong law of necessity acting as a check upon the greater power. (Thomas Malthus, Essay, 1798, chapter 2. The “greater power” is population’s power to grow.)

Chapter II · How populations grow

#### An Essay on the Principle of Population

Malthus, 1798, chapter 2: “population, when unchecked, increased in a geometrical ratio, and subsistence for man in an arithmetical ratio.” He illustrated it with the sequences 1, 2, 4, 8, 16 … and 1, 2, 3, 4, 5 …

In the scene each block is one unit of Malthus’s sequences; the scale is symbolic.

Sources: [Thomas Malthus, An Essay on the Principle of Population (1798), chapter 2](https://www.marxists.org/reference/subject/economics/malthus/ch02.htm)

### Doubling time
*Chapter II · How populations grow*

A rule you can do in your head.

Exponential growth has a simple rule of thumb. Divide seventy by the yearly growth rate in percent, and you get roughly the number of years it takes to double. At four hundredths of a percent, the long average before 1700, doubling takes about seventeen hundred years. At nine tenths of a percent, today's rate, about seventy-seven. At two point three percent, the peak of the 1960s, only about thirty. Press Race to watch all three at once. A doubling time that kept shrinking is exactly what von Foerster saw in his data, and why his curve bent so sharply upward.

$$T_{2} \approx \dfrac{70}{r}$$
- $T_2$: doubling time in years
- $r$: growth rate, % per year

70 comes from 100 × ln 2 ≈ 69.3 (ln is the natural logarithm).

- 0.04% a year: ≈ 1,730
- 0.9% a year: ≈ 77
- 2.3% a year: ≈ 30

- each doubling came sooner than the last
- a fixed percentage cannot do that
- a rising percentage can, until it runs into a wall

Chapter II · How populations grow

#### The rule of 70

For growth at r percent a year, the doubling time is ln 2 / ln(1 + r/100) years, which is close to 70 / r for small r. At 0.04 % that is about 1,733 years; at 0.9 % about 77; at 2.3 % about 30.5.

Growth rates from Our World in Data. The arithmetic is standard; the blocks in the scene are illustrative.

Sources: [Our World in Data: Population growth](https://ourworldindata.org/population-growth); [von Foerster, Mora & Amiot: Doomsday: Friday, 13 November, A.D. 2026. Science 132 (3436), 1291–1295, 4 Nov 1960 (PDF)](https://mozart.bioinfo.rpi.edu/bystrc/courses/biol4961/Doomsday.pdf)

## Chapter III · The billions

### Faster and faster
*Chapter III · The billions*

Until the gaps stopped shrinking.

Look at how the billions arrived. Humanity reached its first billion around 1804. Twelve thousand years earlier, there had been only about four million people on Earth. The second billion took a hundred and twenty-three years, to 1927. The third took thirty-three, to 1960, the very year the doomsday paper appeared. Then fourteen years, thirteen, twelve. Press Add a billion. The eighth arrived in November 2022, about a decade after the seventh. But look at the next gaps: the United Nations expects them to get longer, not shorter.

- **≈ 4 million**: people, 12,000 years ago
- **≈ 595 million**: people in 1700

- 1804: 1 billion
- 1927: 2 billion (+123 years)
- 1960: 3 billion (+33)
- 1974: 4 billion (+14)
- 1987: 5 billion (+13)
- 1999: 6 billion (+12)
- 2022: 8 billion (7 billion in 2011–12)

![Around 2019: about 134 million births and 58 million deaths a year, a net gain of 76 million. AI-generated still.](https://assets.planetpast.com/a/9e/9e4e051000efb78d.jpg)

Chapter III · The billions

#### World population milestones

UN estimates: 1 billion in 1804, 2 billion in 1927, 3 billion in 1960, 4 billion in 1974, 5 billion in 1987, 6 billion in 1999, 7 billion around 2011–2012 and 8 billion on 15 November 2022.

Our World in Data: about 4 million people 12,000 years ago and about 595 million in 1700; around 2019, 134 million births and 58 million deaths a year.

Sources: [Wikipedia: World population milestones (UN estimates)](https://en.wikipedia.org/wiki/World_population_milestones); [Our World in Data: Population growth](https://ourworldindata.org/population-growth); [Our World in Data: World population growth, past and future](https://archive.ourworldindata.org/20251125-173858/world-population-growth-past-future.html)

### Where the curves part
*Chapter III · The billions*

The formula kept climbing. People did not.

Now put von Foerster's curve next to the real numbers. Until about 1960 they track each other closely. Then they part ways. World growth peaked in the early 1960s and has slowed ever since. The formula had no way of knowing that, within a generation, families almost everywhere would start having far fewer children. Instead of the sixty-three billion people the formula gives for 2024, there were about eight point two billion. The doomsday paper described the past remarkably well. It could not see the turn coming.

- 1960, formula: ≈ 2.8
- 1960, UN: 3
- 1999, formula: ≈ 6.6
- 1999, UN: 6

- child deaths falling, so families needed fewer births
- the birth control pill, from the 1960s
- fast-growing cities

- **≈ 63 billion**: the 1960 formula
- **8.2 billion**: UN estimate

![Popular Science also credits the Green Revolution: new high-yield crops that fed the larger population. AI-generated still.](https://assets.planetpast.com/a/a9/a9112281556260c5.jpg)

Chapter III · The billions

#### The turn

Our World in Data: population growth peaked at 2.3 % a year in 1963 and is about 0.9 % now; the global fertility rate has roughly halved. Popular Science (Oct 2026) cites child survival, the Green Revolution, the birth control pill and urbanisation, and quotes demographer Joel Cohen that growth peaked in the early 1960s.

The formula value for 2024 (≈ 63 billion) is computed from the paper’s constants.

Sources: [Our World in Data: World population growth, past and future](https://archive.ourworldindata.org/20251125-173858/world-population-growth-past-future.html); [Popular Science: In 1960, scientists predicted the world would end on November 13, 2026 (13 Oct 2026)](https://www.popsci.com/science/world-end-overpopulation-doomsday-november-2026/); [von Foerster, Mora & Amiot: Doomsday: Friday, 13 November, A.D. 2026. Science 132 (3436), 1291–1295, 4 Nov 1960 (PDF)](https://mozart.bioinfo.rpi.edu/bystrc/courses/biol4961/Doomsday.pdf); [United Nations: UN projects world population to peak within this century (World Population Prospects 2024, July 2024)](https://www.un.org/sustainabledevelopment/blog/2024/07/press-release-wpp2024/)

## Chapter IV · The demographic transition

### Deaths fall first
*Chapter IV · The demographic transition*

Then a gap opens.

So why did the real curve not keep shooting up? Demographers describe a pattern first set out by the American Warren Thompson in 1929. It is called the demographic transition. In the first stage, births and deaths are both high, and population barely grows. Then cleaner water, better food, vaccines and medicine cut deaths, above all among children. Births stay high for a while, so for a generation or two the gap between births and deaths becomes a population boom. Press Next stage to step through.

- 1: births high, deaths high
- 2: deaths fall, births stay high
- 3: births fall too
- 4: both low, growth slows to a halt

![In England, deaths from infectious disease fell from about 11 to under 1 per 1,000 people between 1750 and 1975. AI-generated still.](https://assets.planetpast.com/a/9f/9f9734d3738d477d.jpg)

$$\text{growth} = \text{birth rate} - \text{death rate}$$

Ignoring migration, which matters for countries but not for the world as a whole.

Chapter IV · The demographic transition

#### The demographic transition

Warren Thompson set out the basic interpretation in 1929; Adolphe Landry made similar observations around 1934, and Frank Notestein formalised the theory in the 1940s. Stage 1: high births and deaths. Stage 2: deaths fall fast with better food, sanitation and public health, especially for children, while births stay high, so population grows rapidly.

The curves in the scene are schematic, following the shape of the model, not one country’s data.

Sources: [Wikipedia: Demographic transition](https://en.wikipedia.org/wiki/Demographic_transition)

### Then births fall
*Chapter IV · The demographic transition*

The gap closes again.

In the third stage, births begin to fall as well: the fertility rate, the average number of children per woman, drops. When most children survive, families no longer need many births to be sure that some will grow up. Education, especially for girls, life in cities, paid work and access to contraception all push the same way. In the fourth stage, births and deaths are both low again, and growth slows almost to a stop. North-western Europe went first, from the late eighteenth century. Much of Asia, Latin America and Africa entered the transition later, in the twentieth century.

![Our World in Data: the global fertility rate has roughly halved. AI-generated still.](https://assets.planetpast.com/a/ae/ae52b46e81cbd9aa.jpg)

- children who survive
- girls who stay in school
- cities and rising wages
- contraception

- late 1700s: deaths start falling in north-western Europe
- late 1800s: births start falling in northern Europe
- 1800s: France: births and deaths fall together, no boom
- 1900s: most of Asia, Latin America, Africa

Chapter IV · The demographic transition

#### Stages 3 and 4

Stage 3: birth rates fall, with factors such as access to contraception, rising wages, urbanisation, women’s education and changing values. Stage 4: births and deaths are both low and population is roughly stable; fertility may fall below replacement, leading to an older, shrinking population. A fifth stage is debated.

Deaths began falling in north-western Europe in the late 18th century; births in northern Europe from the late 19th; France was an exception, with both falling together.

Sources: [Wikipedia: Demographic transition](https://en.wikipedia.org/wiki/Demographic_transition); [Our World in Data: World population growth, past and future](https://archive.ourworldindata.org/20251125-173858/world-population-growth-past-future.html)

### The shape of a population
*Chapter IV · The demographic transition*

From a pyramid to a column.

You can see the transition in a population pyramid, which stacks people by age, with the youngest at the bottom, men on one side and women on the other. With many births, the pyramid has a wide base and a narrow top. As births fall and people live longer, the base shrinks, the middle fills out, and the shape turns into a column. Press Young country and Ageing country to compare. Worldwide, a baby born in 2024 could expect to live about seventy-three years, and by the mid-2030s the UN expects more people over eighty than babies under one.

- each bar: one 5-year age group
- bar length: how many people of that age
- a wide bottom bar means many recent births

- **73.3 years**: in 2024
- **70.9 years**: during the COVID-19 pandemic

- **mid-2030s**: people aged 80+ outnumber babies under 1
- **late 2070s**: people aged 65+ outnumber children under 18

Chapter IV · The demographic transition

#### Population pyramids

UN World Population Prospects 2024: life expectancy at birth was 73.3 years in 2024, back up from 70.9 during the pandemic. By the mid-2030s people aged 80 or over are projected to outnumber infants; by the late 2070s people aged 65 or over are projected to outnumber children under 18.

The two pyramids in the scene are schematic shapes.

Sources: [United Nations: UN projects world population to peak within this century (World Population Prospects 2024, July 2024)](https://www.un.org/sustainabledevelopment/blog/2024/07/press-release-wpp2024/); [Wikipedia: Demographic transition](https://en.wikipedia.org/wiki/Demographic_transition)

## Chapter V · A peak this century

### A peak this century
*Chapter V · A peak this century*

And then, slowly, a decline.

The United Nations' latest projections, from 2024, expect world population to keep rising for about sixty more years, to a peak of around ten point three billion in the mid-2080s. Then it is projected to drift down, to about ten point two billion by 2100. Women today have on average about two and a quarter children each, down from about three point three in 1990. Sixty-three countries and areas, including China, Germany, Japan and Russia, have already passed their peak. Projections are not prophecies, but they are built from births, deaths and migration that are measured every year.

- **≈ 10.3 billion**: peak, mid-2080s
- **≈ 10.2 billion**: in 2100, 700 million fewer than projected a decade earlier

- 1990: 3.31
- 2024: 2.25
- replacement level: ≈ 2.1

- 63 already peaked: China, Germany, Japan, Russia …
- 48 peak between 2025 and 2054: Brazil, Iran, Türkiye, Viet Nam …
- 126 still growing past 2054: India, Indonesia, Nigeria, Pakistan, USA …

Chapter V · A peak this century

#### World Population Prospects 2024

UN, July 2024: world population of 8.2 billion is projected to peak at about 10.3 billion in the mid-2080s and fall to about 10.2 billion by 2100. Global fertility is 2.25 live births per woman, down from 3.31 in 1990; replacement is about 2.1. 63 countries and areas have already peaked.

The dashed projection in the scene follows the UN medium scenario’s shape, drawn through its stated values.

Sources: [United Nations: UN projects world population to peak within this century (World Population Prospects 2024, July 2024)](https://www.un.org/sustainabledevelopment/blog/2024/07/press-release-wpp2024/); [UN DESA Population Division: global fertility 2.25 live births per woman, down from 3.31 in 1990](https://www.un.org/development/desa/pd/node/4354)

## Chapter VI · Thailand

### A transition at speed
*Chapter VI · Thailand*

Six children, then two, then one.

Thailand shows how fast a transition can run. Around 1970, Thai women had about six children each, and the population was growing about three percent a year. In 1970 the government made family planning the main way to slow that growth. Within about two decades, fertility had fallen to about two point two children per woman. Today it is about one. In 2024, Thailand registered about four hundred and sixty-two thousand births, the first time below half a million since 1949, and more deaths than births for the fourth year running.

- around 1970: ≈ 6
- 1994: ≈ 2.2
- 2024: ≈ 1.0

![Growth slowed from about 3 percent a year in 1970 to 1.3 percent by 1994, Thailand told the UN. AI-generated still.](https://assets.planetpast.com/a/ac/ac6ee6f1653e5622.jpg)

- **462,240**: births registered
- **571,646**: deaths registered

- **65.95 million**: about 100,000 fewer than a year earlier

Chapter VI · Thailand

#### Thailand’s transition

Thailand’s statement to the 1994 Cairo population conference: the first population policy, in March 1970, made family planning the main strategy; growth fell from about 3 % a year in 1970 to 1.3 % in 1994, and fertility from 6 to 2.2. Department of Provincial Administration figures for 2024 (via Khaosod English): 462,240 births, 571,646 deaths, population 65,951,210; total fertility rate about 1.0.

The Thai pyramid in the scene is a schematic shape, not census data.

Sources: [UNFPA: Statement of Thailand to the International Conference on Population and Development, Cairo, 1994 (PDF)](https://unfpa.org/sites/default/files/resource-pdf/94-09-07_Statement_of_Thailand_H.E._Dr.pdf); [Khaosod English: Thailand’s population drops below 66 million as births hit 75-year low (17 Jan 2025)](https://www.khaosodenglish.com/featured/2025/01/17/thailands-population-drops-below-66-million-as-births-hit-75-year-low/)

## Epilogue

### Friday the 13th
*Epilogue*

The curve that fit the past.

So the doomsday of the title is a date on the calendar, not a prediction to fear. Commentators have suggested the dramatic title was partly a provocation, to make people pay attention. Its lesson still holds: a curve that fits the past very well can still fail, because people can change the very trend that is being measured. The question for this century is no longer how to stop explosive growth, but how to live well in a world that is older, and that is projected one day to begin shrinking.

- 1798: Malthus’s Essay
- 1804: 1 billion people
- 1929: Thompson describes the transition
- 1960: the doomsday paper; 3 billion
- 1963: fastest growth: 2.3% a year
- 2022: 8 billion
- mid-2080s: projected peak ≈ 10.3 billion

- a fixed growth rate doubles in about 70 ÷ rate years
- deaths fall first, births follow: the transition
- a good fit to the past is not a forecast

- **∞**: the 1960 formula
- **≈ 8.3 billion**: people actually alive (Popular Science)

Epilogue

#### Sources

Every number in this film comes from the sources below. UN figures are estimates and medium-scenario projections.

Stills are AI-generated illustrations, not photographs.

The 3D charts are drawn from the numbers in the sources; the pyramids are schematic shapes, not census data.

Sources: [von Foerster, Mora & Amiot: Doomsday: Friday, 13 November, A.D. 2026. Science 132 (3436), 1291–1295, 4 Nov 1960 (PDF)](https://mozart.bioinfo.rpi.edu/bystrc/courses/biol4961/Doomsday.pdf); [Popular Science: In 1960, scientists predicted the world would end on November 13, 2026 (13 Oct 2026)](https://www.popsci.com/science/world-end-overpopulation-doomsday-november-2026/); [The New Daily: November 2026 doomsday prediction (13 Oct 2026)](https://www.thenewdaily.com.au/life/science/2026/10/13/november-2026-doomsday-prediction); [Our World in Data: Population growth](https://ourworldindata.org/population-growth); [Our World in Data: World population growth, past and future](https://archive.ourworldindata.org/20251125-173858/world-population-growth-past-future.html); [United Nations: UN projects world population to peak within this century (World Population Prospects 2024, July 2024)](https://www.un.org/sustainabledevelopment/blog/2024/07/press-release-wpp2024/); [UN DESA Population Division: global fertility 2.25 live births per woman, down from 3.31 in 1990](https://www.un.org/development/desa/pd/node/4354); [Wikipedia: World population milestones (UN estimates)](https://en.wikipedia.org/wiki/World_population_milestones); [Wikipedia: Demographic transition](https://en.wikipedia.org/wiki/Demographic_transition); [Thomas Malthus, An Essay on the Principle of Population (1798), chapter 2](https://www.marxists.org/reference/subject/economics/malthus/ch02.htm); [UNFPA: Statement of Thailand to the International Conference on Population and Development, Cairo, 1994 (PDF)](https://unfpa.org/sites/default/files/resource-pdf/94-09-07_Statement_of_Thailand_H.E._Dr.pdf); [Khaosod English: Thailand’s population drops below 66 million as births hit 75-year low (17 Jan 2025)](https://www.khaosodenglish.com/featured/2025/01/17/thailands-population-drops-below-66-million-as-births-hit-75-year-low/)