Are there places in the world where the population remained pretty stable for thousands of years? I’d assume that each couple would have many babies so how did the population stay stable? Famine, disease, accidents, etc? Or did they keep their number of children low somehow?
Aside from a presumably higher mortality rate due to injury, illness, disability, etc…
One custom is to prohibit sexual relations between partners for a time after birth. That might be a relatively brief interval (say, 40 days) or until the woman stops breast-feeding, which could be a couple of years in primitive societies. That would help to space out children. The problem, of course, is that people what to do the deed so the custom isn’t always observed.
Another custom, which modern folks tend to disbelieve or simply not want to consider, is infanticide. Whether it’s killing kids with a physical defect or simply killing kids that are unwanted, too soon after another, or the wrong gender, it’s actually pretty effective at limiting population.
The population of Australia remained fairly constant for tens of thousands of years. The same was generally true for all hunter gatherer populations. Except for the rare instances of novel technology or environmental change, the population of any area on Earth was approximately stable for dozens of millennia almost everywhere prior to the invention of agriculture.
Disease for hunter gatherers before the late mesolithic was never a major problem, population because population densities were too low to allow easy spread and lack of domesticated animals limited novel sources of disease.
Famine was also, surprisingly, rare. All HGs took extraordinary steps to keep their population within the long term carrying capacity. When you live a small groups, you simply can’t survive if your population crashes every 20 years.
Effective birth control was basically non-existent, so limiting the number of children was of limited effect, although efforts were made.
Population was controlled through two basic factors: warfare and infanticide.
Excess children, especially female children were directly killed or neglected until they died. It’s better to have a child die at 6 months than to feed it for 7 years and then have it die in a drought anyway. The resulting oversupply of pubescent males and the high combat mortality of young men kept populations stable.
At least prior to agriculture, this would pretty much have to be the case: each human needs a certain amount of food, of which a given area can produce only so much.
A primary controller of population in hunter-gatherer societies appears to have been birth spacing via extended breastfeeding.
Warfare isn’t really a good description of what went on in HG societies - they weren’t large-scale enough for wars. A better description would be “murders”. Deaths by violence were reasonably common per-capita, but they weren’t deaths in battle - they would be killings of people mostly personally known to each other (and probably closely related). Also, men and women were both likely victims.
HG societies tended, on average, to be not particularly violent by historical standards - chiefdoms and tribal agricultural/pastoral societies were most violent, followed by HGs, followed by states (modern society is astoundingly non-violent by historical standards, on a percentage basis). Though there was a wide variation - some HG societies were quite violent: the difficulty is in separating out deaths by interactions among HGs, and deaths by interactions between HGs and others. HGs when left to themselves tend to have a middling violence rate - lower than agriculturalists/pastoralists, higher than state level societies.
Your chance of dying by violence in an HG society tended to range between 5-15%, while even in the most violent state, it was a lot less - under 5%.
Round the clock on demand breastfeeding is a pretty good ovulation suppressant…as long as the mother is skinny. If she’s got much body fat at all, she’s got enough estrogen from her fat stores to both breastfeed and trigger ovulation.
So in modern western society, where women tend not to be very thin, and where they often pump during the day and give bottles at night, or supplement with formula, breastfeeding is a crappy form of contraception. But in HG societies, it works pretty well, and births tend to naturally space out by 3-4 years.
The important part to remember is that without some technological/behavioral advance the productivity of a given area cannot increase. If your group is hunting and gathering exactly the same way that people did 300 years ago, and there hasn’t been a change in the productivity of the area, then it can’t support any more people than it did 300 years ago.
Obviously populations can grow rapidly when moving into areas with no humans. So the first people to the Americas or Australia could have population growth because there weren’t any humans there. But once the population reaches carrying capacity the only way to grow the population is some technology that increases the amount of food you can extract from a given place. Note that “technology” should be considered broadly. It’s not just tools, it’s things like setting fires that change the landscape from forest to grassland, which makes it easier to hunt the animals you’ve always hunted in the same way you’ve always hunted them.