Tag Archives: population

7 billion

The world population reached 7 billion around 2011 (although there’s some guesswork involved). Here’s a video about how we got to 7 billion


More than half of the world’s population has been urban since a few years before 2011. About a billion city dwellers are squatters.

Fertility rates have fallen dramatically over the last several decades, even in many underdeveloped countries, although they remain high in Africa and some of the Middle East. Barring catastrophe, world population will continue to grow for some time. (https://brilliantmaps.com/fertility-rates/)

fertility rates

Here’s what the ecological footprint of more than 7 billion people looks like (https://www.pnas.org/content/115/25/6506). The chart shows estimated biomasses of different categories of organisms, in gigatons of carbon. The biomasses of humans, and of human livestock (mostly cattle and pigs), both greatly exceed the biomass of wild mammals and birds put together. The biomass of wild mammals (terrestrial and marine) is only about 1/6 of what it was before humans came on the scene, and total plant biomass is about ½ of what it was before humans, largely as a result of deforestation.


The limits to growth

Different decades have been obsessed with different doomsdays. From the 1940s to the early 1960s, people worried especially about nuclear war. From the late 1960s on, fears of overpopulation and ecological doom came to the fore. John Brunner’s Stand on Zanzibar (1968) is still one of the best science fictional imaginings of a planet cracking apart under the stress of overpopulation, a richly detailed piece of world-building. Like all visions of the future, it reflects the time it was conceived in, carrying a sense that the cultural revolutions of the 60s were spinning out of control.

For non-fiction there was The Limits to Growth (1972). Here is Scenario 1 from the book, generated by a computer model of the interaction of population, resources, industry, food, and pollution. Fiddling with the model suggested that it would be very hard to avoid a massive collapse in one form or other. If the exhaustion of resources didn’t get you, pollution would do the job.

limits to growth

The idea that overshoot-and-collapse is a fundamental recurring pattern in human history continues to be influential. Jared Diamond’s Collapse is a recent expression. Yet one of Diamond’s case studies, Easter island, now seems fairly shaky. And the most famous decline-and-fall of all – that of the Roman empire – also doesn’t look much like a Malthusian crunch. (On Rome, in addition to references in my previous blog posts, check out Goldsworthy and the recent book by Harper.)

None of this is meant to suggest that we shouldn’t worry about our ecological future. Rather that we should be thankful that we’re now getting to be rich enough that we can worry less about immediate subsistence threats and more about distant dangers.

Green revolution

September 1970 – March 1974

The battle to feed all of humanity is over. In the 1970s hundreds of millions of people will starve to death in spite of any crash programs embarked upon now. At this late date nothing can prevent a substantial increase in the world death rate.

Paul Ehrlich. The Population Bomb. 1968

Ironically, it was just around the time that Ehrlich wrote this that production of rice and wheat in India, the Philippines, and other countries was booming thanks to the Green Revolution – more productive plant varieties that could take advantage of fertilizer and pesticide inputs. It’s true, as Malthus pointed out long ago, that exponential population growth can eat up any conceivable increase in agricultural output. But the Green Revolution bought the world some breathing space until birth rates began to come down. It probably also eased some of the paranoia about food supply that played a part in two world wars.

Whoever makes two ears of corn, or two blades of grass to grow where only one grew before, deserves better of mankind … than the whole race of politicians put together.

Jonathan Swift

Baby boom

June 1958 – September 1962

Malthusianism does a pretty good job of capturing the facts of life for our species before the Industrial Revolution. For example, Malthus plus standard economics helps account for some of the historic differences between wheat and rice growing societies. And Darwinism suggests the reason why Malthusianism holds for living things in general: within a population, variants with a higher intrinsic rate of increase tends to replace those with a lower rate, even if the eventual outcome is overpopulation and misery for all. So the field of human behavioral ecology, based on the assumption that people try to maximize fitness, does pretty well in accounting for behavior in pre-modern societies.

But Malthusianism, and the assumption that people are fitness-maximizers, don’t work very well for modern societies. Even as life expectancies and standards of living have been increasing around the world, fertility rates have been declining, falling below replacement levels even in many less developed countries (although rates remain quite high in Sub-Saharan Africa.) The United States mostly follows the general trend, with a long decline in fertility rates over several centuries.

And then there’s the Baby Boom: Birth rates in the United States went up dramatically following the Second World War, then reached a peak in 1957, and continued high into the early 1960s. Young people were marrying early, and having more children. Women were staying out of the workforce to take care of the kids.

baby boom

Here are two popular theories of why the Baby Boom happened that don’t work:

Soldiers coming home. The return of soldiers from the Second World War contributed to an early spike in the birth rate. But the boom lasted too long to be mostly explained this way, and involved a big increase in the total number of babies born, not just people getting around to having babies that they’d put off having earlier.

Women squeezed out of the labor force. Increasing employment and educational opportunities for women are one of the long-term drivers of the demographic transition. So were these factors operating in reverse during the Baby Boom? The data clearly rule this out. Women’s wages actually rose rapidly during this period, and older women, with their child-rearing years mostly behind them, responded by entering the labor market in large numbers. In other words, employers were eager to hire women, but young women, at least, thought they had better things to do.

Instead, the best account we have comes from Richard Easterlin. He proposes that the Boom happened because young men encountered an exceptionally favorable labor market, resulting from the conjunction of several factors. (1) Birth rates fell to low levels during the Great Depression, naturally enough. As a result, twenty years on, employers faced a shortage of native-born young men looking for entry level jobs. (2) In the nineteenth century, periods of high demand for labor saw increases in immigration; levels of immigration tracked the business cycle. But in the mid-twentieth century, legal restrictions made it difficult to increase the supply of labor through immigration. Employers instead had to offer higher wages for entry level workers. Young men felt they were doing well enough – both absolutely and relative to the older generation – to get an early start on marrying, and to support their wives while raising bigger families.


The Baby Boom would be its own undoing however. As the earliest Boomers grew up and started to crowd the job market and the universities, “The Sixties” took off.



We’re now doing one decade per day on the blog.

The Taiping rebellion in China began in 1850 and was finally put down in 1864. It was led by a former school teacher who discovered, after repeatedly failing his civil service exams, that he was the younger brother of Jesus Christ, destined to bring China over to his own brand of Christianity.

The rebellion was by far the most destructive conflict in the nineteenth century. It illustrates a general characteristic of Chinese history: Chinese wars were fewer but more destructive than European ones. China was unified for most of the past two millennia, governed by dynasties which established peace for long periods of time, among a huge population, over a vast area. But when things fell apart in China, whether from invasions (usually involving steppe nomads) or internal rebellions, vast numbers of people died. Here’s a chart comparing estimated numbers of war deaths for major wars Europe (red) and China (blue)  between 1 and 1800 CE. China’s population during this period was somewhat less than twice that of Europe, so even per capita, China’s military catastrophes were more demographically catastrophic than Europe’s.


The Taiping rebellion comes too late to show up on the chart, but cost the lives of about 20 million people.

Tales of the South Pacific


1) Polynesians in America

Before the great Western voyages of exploration, the Austronesian expansion settled new lands all the way from Madagascar to Polynesia. And Polynesian sailors probably got even further east than Polynesia. Scholars have long been aware of archaeological evidence for contact between Polynesia and America. For example, the Chumash Indians who lived around the Channel Islands in Southern California built distinctive, complex sewn-plank canoes unlike anything in the rest of Pacific North America, but very much like Polynesian vessels. And it’s hard to explain how sweet potatoes could have gotten from the New World to the Pacific islands without human contact – floating in salt water isn’t very likely. A recent scholarly review of a wide range of evidence for contact – linguistic, technological, biological – is here.

Ultimately DNA may provide definitive answers, although a report from several years ago that some New World chickens are genetically close to Polynesian chickens now seems questionable. And recent research found no Native American DNA in Easter island skeletons predating European contact.

2) The Statues That Walked.

Easter Island was settled around 1200, based on the most recent carbon-14 dates. (Earlier dates, going back as early as 300, are apparently mistaken.) There are two very different accounts of the subsequent history of the island. Jared Diamond offers a cautionary tale of ecological overshoot and collapse. After the initial settlement, the island’s population boomed. Without Dr. Seuss’s Lorax to advise them, the islanders cut down all their palm trees.


With no more wood for sledges or rollers, the famous moai statues could no longer be moved from their quarries. And with no more wood for boats, fishing and inter-island trade became impossible. The loss of forests also led to soil erosion. A famine-stricken population rebelled against the hierarchical social order, and wound up resorting to cannibalism in the midst of a population crash. “Easter’s isolation makes it the clearest example of a society that destroyed itself by overexploiting its own resources.”

But Terry Hunt and Carl Lipo, anthropologists who have worked on the island, differ on almost every part of this account.


They suggest that the deforestation of the island resulted from the introduction of rats, accompanying the first colonists. Rats, with no natural enemies to limit them, ate tree seeds. This wouldn’t have had noticeable effects at first, but eventually led to the forests not replacing themselves. Hunt and Lipo also dispute the claim that pre-contact Easter Island experienced a population crash; they argue that the crash came later, with European contact and the introduction of diseases to which the population had no resistance. They also see little evidence of over-exploitation of the environment. Locals were doing the best they could to make a living under marginal conditions. And as to how the moais got from one place to another, well … the islanders said they walked.

This video shows they could be right.

And some back-and-forth between Diamond and Lipo and Hunt is here.

Enjoy it while it lasts

101-205 CE

If a man were called to fix the period in the history of the world, during which the condition of the human race was most happy and prosperous, he would, without hesitation, name that which elapsed from the death of Domitian [96 CE] to the accession of Commodus [180 CE]. The vast extent of the Roman empire was governed by absolute power, under the guidance of virtue and wisdom. The armies were restrained by the firm but gentle hand of four successive emperors, whose characters and authority commanded involuntary respect.

Edward Gibbon, The Decline and Fall of the Roman Empire, Chapter 3

Gibbon doesn’t include China in this assessment of the state of the world, but for that country too, under the Eastern Han dynasty, there was a period of stability and prosperity, lasting from the death of the usurper Wang Mang in 24 CE to the outbreak of the Yellow Turban peasant uprising in 184 CE. During this time, the Roman and Han empires so completely dominated their respective portions of Eurasia that they enjoyed relative peace. Toward the end of the second century CE, both empires had populations around 50-60 million; world population was perhaps 190 million. In the succeeding centuries both empires would experience major population declines and political collapse. As a result, the world’s total population may have declined as well.

Of course Gibbon’s view is a retrospective one, and didn’t anticipate the vast rise in standards of living that eventually followed the industrial revolution.

(After this I’ll give dates as numbers without the “CE”.)