Demography and Destiny

In this essay, I will make the case that demographic transition theory is wrong.

Demographic transition theory (DTT) proposes that people go through a transition from high fertility to low fertility as their societies modernize. Supposedly, this will lead to a stable or declining world population at some point in the future. This assumption is built into UN population projections.

DTT fits the evidence of recent history. Over the last 100 years, fertility rates have fallen dramatically as modern civilization spread around the world. Today, most parts of the world have low or declining fertility.

What caused this change in human behavior?

The generally accepted view is that poverty causes high fertility, and so alleviating poverty causes lower fertility. According to this view, poor people choose to have more children either to help on the farm, or to care for them in old age. They also have extra children to replace those who die young. If poverty is alleviated and childhood mortality is lowered, people will choose to have fewer children.

This view is rather strange. It assumes that people have children based on rational economic calculations, and that those choices are mostly based on concern for their own welfare, as if children were a means to an economic end, rather than vice versa. It does not make sense biologically, psychologically or economically. It also doesn’t fit the evidence of history.

It isn’t biologically plausible, because life forms are shaped by evolution to reproduce. Thus, abundant food should cause population growth, not population stability or decline. And that is what we observe in nature. An expansion of the food supply causes population growth for every other species. There is no theoretical reason why humans should be exempt from this general principle. Also, there have been human population explosions in the past, when food production increased.

It isn’t psychologically plausible, because parents don’t view their children as economic assets. We evolved to reproduce, not to accumulate wealth for its own sake. Parents invest much more labor in having and raising children than they could ever get back. Likewise, it is implausible that parents have extra children to compensate for child mortality. Would you have more children if you believed that they were likely to die young?

People have children as a consequence of sex. Parents then bond with their children, and work to protect and support them. Human action is driven by emotions, not by economic utility calculations, and emotions evolved to make us reproduce.

Reproduction requires parents to invest in children, not vice versa. There may be some energy flow back to parents later in life, but it is relatively small compared to the energy invested in children by parents. Energetically and economically, children are a net cost to their parents, not a net benefit.

Some cultures have a myth that children are economically beneficial to their parents, but that is only a myth. There are various reasons why cultures might have this myth. It promotes reproduction. It promotes children taking care of parents rather than dumping that burden on society. Elderly parents are a good source of wisdom, and typically help to take care of their grandchildren. Like many myths, it rationalizes adaptive behaviors, even though it is not true.

The idea that wealth causes decreased fertility is not consistent with the evidence of history. There are many historical examples of improved living standards causing an increase in human fertility, not a decrease. The Irish population expanded rapidly after the introduction of potatoes. French and English settlers in the Americas adapted to conditions of abundance by increasing their fertility. Women married younger and had more children, and the population of Europeans in the Americas expanded rapidly. Until recently, families with 10 or more children were common in Quebec.

See Study shows humans still evolving.

Even though there was a general decline in fertility across the developed world in the 20th century, fertility rates fell faster and went lower in communist Russia than they did in in the much wealthier United States.

So, there is no reason to believe that increased wealth causes decreased fertility in human beings, although in recent times there has been a correlation between them. The recent correlation between increased wealth and decreased fertility must be due to something else.

A more plausible explanation is that low fertility increases wealth. With fewer children, there is more energy to invest in creating capital.

Low fertility might have played a role in the industrial revolution in Europe. Western Europeans had lower fertility than most other people around the world, due to the Western European marriage pattern. In Western Europe, women would often delay marriage and children until their mid-twenties. The result was lower fertility and more energy to invest in the creation of capital. Capital increases the efficiency of labor, which allows for even more investment in capital, but only if the population does not expand to consume the additional production. The industrial revolution was one of the few times in human history when economic growth outpaced population growth, leading to prosperity.

The recent Chinese economic boom might also be partly due to lower fertility. After the communist revolution, there was a huge decline in the Chinese fertility rate. Roughly a generation later, the Chinese had a huge economic boom due to rapid industrialization. This is usually explained as the result of China adopting market-based economic policies. However, I believe that lower fertility played an important role. It shifted labor from the creation of human beings to the creation of capital.

The generally accepted explanation for the observed modern decline in fertility is incorrect. It is based on a flawed conception of human nature.

Birth control is the main cause of the modern decline in fertility. Human emotions evolved in a world without birth control, a world in which lust caused us to have sex, and having sex caused us to reproduce. When sex is decoupled from reproduction, fertility collapses. Human emotions don’t make people choose to have lots of children, or have children at all, because reproduction did not depend on that choice in the past. By giving people more control over reproduction, birth control broke human nature.

Cultural and social changes also contributed to fertility decline. Traditional beliefs and ways of life centered on the family. Modern beliefs and ways of life center on the individual, as a producer and a consumer. Industrialization and urbanization made it possible for women to work outside the home. Marriage was secularized, and divorce was made easier. A new way of life emerged, which involved an extended youth, wage employment and consumerism. People came to view parenthood as a personal choice, rather than a natural and almost obligatory part of life.

Birth control, combined with cultural and social changes, caused the modern collapse of fertility.

Why do people believe in DTT?

DTT plays an important role in the humanist worldview. It is part of a “don’t worry, be happy” view of human nature and reality. Humanists believe that low fertility is a sign of progress and enlightenment. They believe that people will naturally choose to have fewer children if they are liberated from economic, cultural and social constraints.

In the humanist worldview, low fertility has two benefits. One is that it frees the individual to pursue happiness or “self-actualization”. Somewhat ironically, humanists view the creation of new human beings as a burden to be liberated from. Low fertility also eliminates the social and global problem of population growth, and the resulting conflict over finite resources.

Humanists believe that human nature is essentially good and rational, and thus human nature should produce good and rational outcomes if it is liberated from constraints. So, it is easy for them to believe that low fertility is due to human nature being liberated from ignorance and poverty. And it is true, in a sense.

However, the “liberation” of the individual from parenthood also alienates him from his natural purpose. It is maladaptive. It raises a philosophical question: what is the purpose of life? Also, voluntary low fertility is self-eliminating. In the long run, it does not solve the problem of population growth and scarcity.

Now that I have described DTT and its importance to the humanist worldview, I will explain why it is wrong. I have already explained some of the problems with it. Now I will explain why the predicted demographic transition will not happen.

To put it simply, DTT is wrong because it ignores evolution. Human beings are not magic. Evolution applies to us, as it applies to all living beings. Modern civilization does not transcend evolution.

Those who reproduce pass on their genes and memes to their children. In the long run, voluntary low fertility will be corrected by evolution, because it is maladaptive. Those with low fertility will simply be replaced by those with higher fertility. Voluntary low fertility is not stable, so it will not persist. It is self-eliminating.

The best reproductive strategy is the one that maximizes the number of offspring that survive to reproduce themselves. In hard times, parents can do better by having fewer children, because they can invest more in those children, giving them a better chance of surviving to adulthood. Conversely, when times are good, it is adaptive to have more children. In modern times, almost all children live to adulthood, and thus high fertility is the best reproductive strategy. A woman on welfare who has six kids with five baby-daddies is biologically superior to a career woman who has one child.

Today, fertility rates are still declining in most parts of the world. The meme of low fertility is propagating as part of a cultural package. It does not propagate well from parents to children (for obvious reasons), but it can propagate from peer to peer by imitation and communication. Most people find the modern, low-fertility lifestyle appealing. So, at the moment, low fertility is replacing high fertility. However, this is a temporary effect, not a transition to a new, stable way of life.

A meme that causes low fertility is like a disease. It selects for traits that make people resistant to it. The people who adopt this new way of life leave behind few descendants. By contrast, those who reject the low fertility lifestyle leave behind more descendants. In the modern environment, any genetic or cultural trait that causes high fertility is selected for. That may include traits that we think of as individually or socially harmful, such as low IQ or psychopathy. Such traits will increase if they cause higher fertility.

In the long run, the human population will evolve resistance to the meme of low fertility, just as we evolved resistance to other diseases. This will occur by some combination of biological and cultural evolution. Low fertility is not evolutionarily stable, and thus it will not persist. Even if we go through a demographic transition, it will not be a permanent condition, but rather a temporary effect of modern civilization. Like any new disease, it will sweep through the population, infect susceptible individuals, and leave behind a population that is resistant to it. Higher fertility will evolve, either culturally or biologically. More fertile people will replace less fertile people. More fertile traits will replace less fertile ones.

For example, Islam is expanding rapidly due to population growth. That is because Muslims, and especially fundamentalist Muslims, have higher average fertility. They keep women in the home making babies. The Muslim world has grown more fundamentalist in the last 50 years, mainly because fundamentalists had more children than secularists and moderates in Muslim societies. Islam is now spreading to the West, due to population pressure. Muslims are replacing the declining native population of Europe, which has very low fertility.

See Why Muslims are the world’s fastest-growing religious group (Pew Research).

The Amish are another example. Their current rate of population growth corresponds to doubling every 20 years. That is entirely due to high fertility. (There is very little conversion into the Amish community.) At their current rate of growth, the Amish population would exceed the current world population in less than 300 years, starting from its current size of 250,000. If everyone else went through the demographic transition except the Amish, then after 300 years the global population would be almost entirely Amish.

In spite of being anti-modern, the Muslims and the Amish are adapted to the modern world. They reproduce their genes and their memes. As time goes on, other adaptations will emerge. One thing is certain: humanity will not settle into a stable pattern of low fertility unless we impose it on ourselves.

Demographic transition theory is wrong because it ignores evolution. It assumes that there is a single, fixed human nature. That assumption is false. There are variations within human nature, and human nature is not fixed. It evolves. Human nature was shaped by evolution to make people reproduce, not to be happy or self-actualized. Human nature will continue to be selected for reproductive fitness. We cannot transcend evolution.

There is only one way to have persistent low fertility, and that is for society to impose it on individuals. In the long run, population growth is a tragedy of the commons. Social regulation of individual behavior, imposed by coercion, is the only way to solve a tragedy of the commons. If we want to maintain the modern condition of prosperity in which most children live to adulthood, then we have to socially regulate reproduction.

With eugenic reproduction control, we could maintain a stable population and a stable or improving genome. Otherwise, population growth and dysgenics are guaranteed to bring about the collapse of modern civilization. If that happens, we will return to the condition in which the human population is limited by premature death.

Those are the only possible destinies for humanity. We can still collectively choose one or the other, but time is running out.


  1. 1. Historically high wealth was indeed positively correlated with fertility, but without capitalism/female emancipation, wealth plays a very different role. The Marxist view here is probably the right approach.

    2. Children investing in parents: definitely plausible from a selfish perspective. In pre-literate societies, technological/cultural/geographic/etc knowledge is concentrated in old people. Knowledge takes a long time to transmit. Tons of case studies in the anthropology literature. Nestor in the Iliad!

    3. Birth control: mormons have access to it, orthodox jews have access to it, etc. Its existence is important, but you have to have a population willing to use it. Can't be the cause; the will not to have kids comes first.

    That said, obviously you're right about the long run...this is unsustainable. There's still differential fertility, so selection is doing its thing and we're eventually gonna start hitting Malthusian limits again. But the AIs will have eaten us by then, so who cares.


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