This link in /r/videos on the demographic transition and overpopulation is surprisingly well-researched and supports non-populist conclusions at a time of heavy populism, so I'm somewhat conflicted about writing this R1. But I think the video is wrong and should be corrected, though it's wrong in a reasonable way that has a lot of expert support behind it. Let me just say at the outset that a lot of people's concerns about overpopulation are poorly formed, and in some cases are nothing more than uninformed racism. I don't support these interpretations of overpopulation as a threat and none of this should be interpreted by their proponents as a providing shelter to their ideas.

I found a fantastic link online that will automatically extract the captions of YouTube videos, and I'll be quoting from it for the rest of this post. The transcript can be viewed here.

This video is arguably less badeconomics and more just overconfidenteconomics. I would consider the two almost interchangeable, but you might not. Nitpickers and methodological terrorists and the endogeneity Taliban will probably like this post. Functional human beings might not, I wouldn't know.

Specifically, near the end of the video, the narrator claims

So as this generation gets older, and fertility declines further, the rate of population growth will keep on slowing. This is true for every country.

My hope is to convince you that this statement is very overly bold.

I'm going to summarize the video sequentially by quoting it. Initially, it claims:

By today's standards, Europe was worse off than a developing region, suffering from poor sanitation, poor diets, and poor medicine. A lot of people were born, but lots of them died just as fast, so the population hardly grew. Women had between 4 and 6 children, but only 2 of them would reach adulthood.

And then

People went from being peasants to workers. Manufactured goods were mass produced and became widely available. The sciences flourished and advanced transportation, communication, and medicine. The role of women in society shifted and created the conditions for their emancipation.

Slowly this economic progress not only formed a middle class, but also raised standards of living and health care for the poor working population. The second transition stage started. Better food supplies, hygiene and medicine, meant people stopped dying all the time, especially so, at a very young age.

Finally

The main reasons families used to have lots of children was that only a few of them were likely to survive. Now that had changed, so the third stage of transition was set in motion.

Fewer babies were conceived, and population growth slowed down. Eventually a balance emerged, fewer people were dying and fewer children were born, so the death rate and birth rate became stable. Britain had reached the fourth stage of the demographic transition. This didn't only happen in the UK, more and more countries went through the four stages.

What's wrong with this narrative? Several things. Perhaps most importantly, conjunctive predictions are bad. (See "assessing probability of a scenario". Then go read the entire book, it's amazing.) There are several obvious candidates for necessary conditions for the demographic transition model to apply. Even if we're 90% confident that each of these conditions have been met for all countries, in combination that makes the overall prediction suspect. I'd encourage you to try for yourself assigning various probabilities to claims, then multiplying them as you believe they are necessary to the demographic transition model. Keep in mind that these claims are supposed to apply to all countries.

I'm going to try to go into more detail while keeping this as organized as possible, but organization is a difficult struggle for me.

A1. One thing that seems important to the video's claim is that the cause of an increase in a country's birth rate is assumed to be increased economic growth. This was true in the case of the UK. But in many countries, it has not been the case. Exported technologies like vaccines have allowed countries to curb their infant mortality rates without first improving their economic growth. This undermines the prediction that rising standards of living will accompany increased birth rates, and that in turn is important to their claim that birth rates will level out over time. See this link for an overview of some prominent ways in which exported medical technology and charitable aid has helped reduce infant mortality in Africa.

You might want to claim that even if economic growth is not necessarily the cause of a country's increased birth rate, a country's increased birth rate will result in increased birth rates. But the evidence for this popular idea is murky. Even assuming that the idea is correct, the relative magnitudes of all these effects are important. A small amount of economic growth occurring as the consequence of a large bump in population growth may not adequately compensate for problems incurred. I can also imagine that the regional distribution of births could be important, as in rural vs urban. Those sort of patterns may have changed due to technology. Maybe not, of course. But in the broad overview of the video it's impossible to take possibilities like this into consideration.

A2. I would also point out that it's moderately likely the countries who have not yet gone through a demographic transition differ in important ways from the countries who already have transitioned. Much of the low-hanging fruit may be taken. As an example, Sub-Saharan Africa seems to be stubborn to transition.

B. As a general note, it should go without saying that a lot of our data in developing countries are questionable. Making high-confidence statements about the current nature of these countries is risky, and predicting future trends on that basis is even riskier. If you're interested in this, you might try tracking down some of the works cited in this book.

C1. A second large problem with the video's description of the demographic transition is the causal motivation it provides for families to have children. We are told that families had lots of children in order to guarantee that at least some of them would survive to adulthood, but once infant mortality decreases this will be unnecessary, and so we will see population growth slow. This portrays parents as rational fitness maximizers who are doing their utmost to guarantee the spread of their genes (rather than as rational utility maximizers - these are thematically similar but still very different motivations because happiness is not a perfect proxy for fitness, which is why ice cream exists). This perspective asserts that parents will stop having many children if having many children becomes unnecessary to guaranteeing they have two or so children survive to adulthood. There are a few problems with this.

C2. This understanding of human motivations for sex is overly narrow. It can't explain instances where couples choose to have sex for fun and use birth control and never have children, for example. It simultaneously ignores the connection between religiosity and increased birth rates, even though we know that some religious groups encourage members to have more children.

C3. Furthermore, even if prosperity has so-far tended to increase the number of children that individuals choose to have, we can only tentatively treat this generalization as a law that the future will follow. This paper looks pretty tentative, but suggests that there may be a U-curve associating wealth and birth rates in Europe, rather than just a straightforward decline. So in the longer run, overpopulation might still turn out to be a problem, even if in the next fifty to one hundred years it is not. Distinguishing these is important.

C4. Even if we accept the premise that better off people will want to have fewer children, important mediating factors allowing them to achieve this desire are ignored by the video. Increasing education, accessibility of birth control, and empowerment of women are by no means definitively associated with increased economic growth. It's a really lazy sort of historical determinism that says condoms/abortion rights and prosperity go hand-in-hand, because it requires ignoring all the ways in which these things are controversial in prosperous countries today, and are uniquely controversial in some developing countries. I could dig up more links on this but this post is too long already. Suffice it to say fundamentalism is really strong in Africa and I see no signs it's going to somehow fade. Whig history is bad. There's no reason given by the video that we should see secularism, increased prosperity, the rise of women's rights, or birth control accessibility continue to rise. Some of those things seem to have been associated with each other so far, but that's not strong evidence they'll all continue to happen and associate with each other in the future. We should not be 100% confident in any of these things. In some cases, I think we should be significantly less than 50% confident in these things. I hate oversimplifications like this.

C5. One country that stands out to me as potentially invalidating their general analysis is China. China is currently undergoing an aging crisis and suffering a severe gender skew due to their one-child policy. They have a strong incentive to boost their birth rate very quickly, and have been implementing programs aimed at incentivizing this. Maybe these attempts are doomed to failure, I don't know, but it seems like a reasonable possibility to be concerned about. The important point is that possibilities such as this can't just be dismissed a priori based on what your historical model tells you. It requires specific investigation of what's actually going on in various areas.

D. China, and other developing countries, are important because we should be assessing the consequences of their growth in terms other than just raw population count. What we are really interested in is the consequences that countries' demographic trends will have on the environment. That means we should be analyzing things like changes in their consumption habits as well, and hurts further the earlier idea that economic growth accompanied by declines in the birth rate will necessarily be good. The historical approach of the video hamstrings it from looking at the problems directly associated with population growth today, that no one knew to be concerned with in the past, like Global Warming.

Is it morally unfair to say to people living in developing countries people for us to say that it was okay for us to go through a demographic boom followed by a slowdown as our standard of living rose? Kind of. Does this change the possible consequences of such transitions occurring elsewhere? Not at all. I wish that it were possible that every country would be able to move through the four stages of the demographic transition model and arrive at a large, rich population. But I'm far from certain this is the case, and you should feel the same.

Feedback highly appreciated, especially regarding organization. I'm really bad at organizing my thoughts for other people to read. Also, if moderators want to implement some kind of Super Flair or something anytime soon, and feel like giving me that for this post, that would be nice. :^)