Sexuality Stack Exchange Archive

How did populations of primitive people remain stable?

Alternate title: “How did primitive people [control population/keep population stable]?”, but this implies that they did it consciously, and that it was a matter of control. I don’t want to make either of those assumptions.

We have a huge technological advantage for population control compared to primitive people. We have latex condoms, birth control pills, and an understanding of fertility that far surpasses what our distant ancestors had. According to Sex at Dawn, primitive people may also have had more sex than modern people. I think they started having sex at an earlier age, but I don’t have a reference. They had better nutrition than moderns, which should lead to increased fertility. According to they research of Price and Pottenger, they had easier births with fewer deaths.

In all these regards, they should have been producing a lot more babies than we make today. And yet, their populations didn’t grow, while today we have 7 billion humans on the earth. Why?

Wikipedia says “hunting and foraging, a lifestyle that by its nature ensured a low population density”, but does not explain how that happens. I am confident that starvation was not the mechanism, nor endless bloody warefare, nor short lifespans, regardless of Hobbes.

Also, I recognize that “primitive people” actually describes an extremely diverse set of cultures, so there may not be a single answer.

(By primitive, I mean pre-agricultural, so don’t mix in the middle ages or anything!)

Answer 108

This actually comes from a number of different factors. This digs a lot into anthropology though, and less on sexuality, but I'll try to be thorough in my answer and cite as many sources as possible. Since, however, it isn't very easy to get life expectancy data from the eras in which you are talking as it must be taken from skeletons and other such sources, it has to be extrapolated a little bit going backwards. So bear with me a little.

Maximum Sustainable Yield

The maximum sustainable yield (MSY) in terms of populations is the highest number of people that can be sustained given the available food and resources. This is observed not only in humans, but in all populations, and usually ends up looking like the following:

Maximum Sustainable Yield: Credit Wikipedia

Image credit Wikipedia.

Now, this graph here is a very simplified theoretical graph, and, as we all know, they don't align properly to real life all the time. Now let's look at the human population graph.

Human Population over time

Image credit University of Maryland Department of Geology (really)

This is the best chart I can find for human population. You'll notice that human population really leveled out there (essentially) for thousands of years. You didn't see that combinatorial growth until the industrial revolution. Minor bumps here and there, and you see increases 2000 BC and around 0 AD but the real growth you could expect is around the industrial revolution. That is when the MSY sky rocketed. Before this time you had minor inventions which certainly helped increase the MSY, but nothing like in the industrial revolution. At that point we were able to produce enough food, shelter and other necessities to be able to sustain livelihoods in a consistent manor. This is what has allowed the population to grow now, and what prevented it from growing before. More kids meant either you or they starve. Which did happen, frequently. And that leads us to...

Disease and Mortality

Disease really starts to set in more later, but we'll cover it a bit. The industrial revolution helped spread diseases amongst people faster as people were now grouped together more closely. But one of the issues of being a hunter/gatherer society is needing to be on the move. And while on the move there are many things that can kill children very quickly. Animals, cold, getting lost, even eating the wrong berries. This ebook, though missing a few pages, seems to have some pretty good information about the topic. Including the following equation on page 313 pertaining to the survival chances of children in hunter/gather societies.

Equation for child survival rate

This book focuses more on the sociological aspects of their survival, but that will play into this significantly as well.

Now for mortality and life expectancy. I was trying to not use Wikipedia as a reference if I could help it, but they actually have a really good chart on this on the Life Expectancy article.

Life Expectancy Chart

Chart Credit Wikipedia

You'll notice that, as children, there is a higher mortality rate, as indicated often by the notes (once the get to 15, they are expect to live...). And while this chart takes into account childhood mortality rate, it does not take into account pre-natal mortality rate. With advances in modern medicine, giving birth has had a much higher success rate (source).

You'll notice in the chart, the Neolithic age has the lowest life expectancy of any other age. And this, mostly, is the age in which you are discussing. Many children born never reached sexual maturity and therefore could never produce offspring. This meant that the population never grew exponentially as you might expect if each of two or three children would have two or three children.

tl;dr

In my research for this, I did stumble across a paper that seemed to be talking directly to what your question gets at, and is actually where some of the data for the life expectancy chart comes from. The Neolithic Revolution and Contemporary Variations in Life Expectancy by Oded Galor and Omer Moav seems to answer your question (a little side-ways since their focus is on life expectancy, but still). Specifically, on page 5, footnote 12, it says:

As is well established in the evolutionary biology literature since the seminal work of Lack [1954], the allocation of resources between offspring ‘caring’ and ‘bearing’ is subjected to evolutionary changes. Lack (1954) suggests that clutch sizes (e.g., number of eggs per nest), among owls and other predatory vole-eating birds, for instance, are positively related to food abundance. He argues that the clutch size is selected such that under any feeding conditions fertility rates ensure the maximal reproductive success. Furthermore, Cody [1966] documents the existence of significant differences between clutch sizes of the same bird species on islands and nearby mainland localities of the same latitude. In temperate regions where food is more abundant in the mainland than on islands, the average clutch size is smaller on the islands. For instance, Cyanoramphus novaezelandeae, the average mainland clutch is 6.5 whereas the average in the island is 4.

Which is basically what I was discussing with the MSY above. I didn't get a chance to read through all of it yet, but the parts I did read seem to discuss their points with a fair bit of depth. At the very least, I've got it bookmarked for myself for later.

So, in short, it wasn't necessarily about how much sex they were having and their fertility, but more about how long they could survive and how many people could be sustained which contributed to a somewhat stable population number.

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