Here is the quarterly change in population of the United States:
Every year, like clockwork, population increases a lot in summer and then increases at a significantly lower rate in winter. Why? Here are births and deaths:
Every year, births peak in summer and hit a low point in winter. Deaths peak in winter and hit a low point in summer. Here's how it all nets out:
Every year, net population increases most in summer and least in winter. That pattern collapsed during the COVID epidemic as deaths skyrocketed during various surges, but has now returned to normal with ordinary peaks in 2022 and 2023. However, the peaks have been steadily declining since 2015 as we have fewer and fewer children.
POSTSCRIPT: On an unrelated note, the CDC makes it all but impossible to get monthly birth figures for more than the past couple of years. I have no idea why. If I didn't fall into dumb obsessions fairly easily I would have given up long before I finally managed to retrieve them.
Doctor Who Christmas specials linked to lower death rates,
https://www.telegraph.co.uk/news/2023/12/18/doctor-who-christmas-specials-lower-death-rates-bbc/
Despite the entirely inaccurate title of this article,
https://nordot.app/1116820132661494494?c=592622757532812385
This study demonstrated that meditation had little impact on elderly well-being, except one specific exercise meant to enhance a sense of loving kindness, which may compliment the suggested influence of Doctor Who.
I've read that nothing reduces a population in the long run like lower birth rates. Not war, not famine, not disease.
The exception to this are wars of extinction, such as those fought by some primitive tribes.
Geez, I dunno about that. It would depend a lot on what you mean by "the long run<' and we don't really have great demographic data for a lot of past societies. But here's what we do know. Epidemic disease reduced the population of native Americans, Hawaiian, and Chamorro (probably other Polynesians as well) at an apocalyptic rate. That had nothing to do with birth rates. OTOH, Japan vastly reduced its birth rate between 1600-1700, and that didn't reduce the population at all. Rather, it slowed the birth rate, but because the economy grew faster than the population did, real personal income increased and life expectancy also increased, so the population still increased... slowly. There's a pretty well known book about just this topic.
Also, I'm not sure about wars of extinction between primitive societies. Do you mean pre-agricultural people, or neolithic people, or bronze age people, or what? Mainly, very early people weren't capable of carrying out wars of extinction unless their enemies were already a pretty small population. The Mongols, on the other hand, they could have done it. But they weren't a primitive people.