Demography and Destiny

The point of the essay is that fertility will eventually increase again, if enough time passes, even if that takes several generations.

It may be true that culture can evolve faster than genes, but culture is not homogenous, so I don't think we can predict that all subcultures will evolve to adopt low fertility memetics. Eventually, the low fertility memetics and the people who practice them will slowly die out. The essay also gave examples of how the fundamentalist Muslims, the Amish, and Ultra-Orthodox Jews have some of the highest fertility rates in the world. Even if most people adopt low fertility, the most likely prediction is that the factions that have higher fertility rates will gradually replace them until they become the new majority of people.

Actually, I have a few last points to say.

It's a dubious assumption that fertility decline is caused mostly by birth control. Fertility declined long before birth control became widespread.

That's simply not true. If you read Wikipedia and its external sources, you would learn that birth control was actually increasingly common in the developed world during the 1800s. So, it's logically sound to conclude that increased birth control was the real reason why fertility rates declined across the developed world during the 1800s and early 1900s. Birth control practices were also generally adopted earlier in Europe than in the United States.

Also, if you ask any parent who has a child, they will testify that their birth rate was low when they were using birth control, and that their birth rate increased when they stopped using birth control. It really is that simple.

As soon as we forget that birth control was what enabled women to pursue higher education and career advancement in the first place by liberating them from childcare, it's very easy to over-complicate all this and come up with beliefs that don't accurately explain why fertility rates decreased over the past 200 years. Any population that deliberately avoids birth control is guaranteed to have an extremely high fertility rate in the modern world.

So yes, birth control was the true reason why fertility rates declined in the developed world in the last 200 years. Birth control was invented for a reason: to avoid overpopulation.

The first is that fertility decline is caused mostly by birth control.

If birth control hasn't been enabling fertility rates to decline, then what has? Birth control has existed ever since the Ancient Egyptians. However, the increasing availability of the birth control pill, other contraception methods, and the legalization of abortion during the 60s and 70s (in the US) are notable for contributing to the declining fertility rates in the US.

The essay also argues that reductions in wealth cause declines in fertility rates. In the last century, we can observe this during the Great Depression, the Great Recession, and the Covid-19 lockdowns.

The second is that high fertility memes are durable. But usually exactly the opposite happens.

No, the opposite doesn't usually happen. For all of human history, higher fertility memes have tended to outlast lower fertility memes. Some maladaptive memes do persist, but that's mainly because it takes a long time for them to die out. By way of analogy, smallpox maintained a TFR of 30% after millennia of infecting humans.

Now of course, the last 200 years are exceptional, since many lower fertility memes have overpowered higher fertility memes. But exceptions to the rule don't disprove the rule, especially when the timescale has been too short since the Industrial Revolution to see how everything will eventually play out. We are living in the most exceptional times ever in all of human history.

"cultural change causes lower fertility" is the same as "high fertility memes lose"

We can think of memes using the traditions | fashions dichotomy. Eventually, the fashions will die out, after enough time passes.

Mormons used to have much higher fertility, and now they don't.

Yes, that's mainly because more Mormons are using birth control. And yes, some higher fertility memes are losing their ground to lower fertility memes, but there's also many high fertility memes and memeplexes that still have very high fertility rates, such as the fundamentalist Muslims, the Amish, and Ultra-Orthodox Jews.

But industrial civilization can collapse due to low population long before natural selection would cause fertility to rise again.

I'm worried about this too to some extent. I've written a list of things that could be done to boost Western fertility rates.

With TFR 1.2 (like in Italy now) population would drop below 100 million in about three centuries.

What population are you referring to?

I disagree. I think that access to birth control is the main factor that has been affecting fertility rates because birth control is necessary to enable the modern lifestyle that you're talking about. As a thought experiment, if all the world's birth control instantly disappeared, then it would be normal for everybody who has heterosexual sex to have large families, especially since modern technology ensures that nearly all infants live to adulthood. I've written some more detailed explanations in my Population Dynamics FAQs.

Although it's a common belief that the Covid lockdowns increased birth rates for the reason that you describe, it's actually false. The US Census Bureau recorded that birth rates declined during the lockdowns because people became poorer. This is consistent with my theory of population dynamics. My theory predicts that people have more children when they become wealthier, and they have fewer children when they become poorer. As the linked post explains, there is a better explanation as for why there's a negative correlation between wealth and fertility rates.