Humans have adopted different strategies depending on lifestyle.
For example - hunter-gatherers, allegedly, breastfeed for longer than agricultural peasants, with the effect (intended or not) that the birthrate for HGs is lower.
In social-evolutionary terms this makes sense, as HGs are on the move more, and so a family would have a harder time caring for a bunch of helpless kids at once; agricultural societies, in which the family stays put in one place, can afford less to have birth-spacing: parents can physically take care of a bunch of more or less helpless kids at the same time.
I suspect children also begin to be an economic net earlier for the agricultural worker–even a 5 or 6 year old can help a lot on a farm, taking over tasks that otherwise more capable adults would have to do. Even just standing in a field scaring off crows makes a difference. I don’t know when hunter/gatherer kids start generating more food than they eat.
For the non-infallability of the pill : Birth Control - Options for Sexual Health.
(I have no idea of what the source means by “theoretical effectiveness” – but even that is less than 100%).
Archeological evidence, written records for as far back as writing existed, and educated guessing based on current people with similar lifestyles.
If you define “early humans” as from from 200,000 years ago to when agriculture was invented (with happened more than once, actually) which was (very roughly) about 15,000 to 10,000 years ago, then statistics are skewed by high infant mortality.
Based on modern hunter-gatherers, such early humans probably matured sexually slightly later than we currently do. On the down side, infant mortality was high and birth defects now considered mild/correctable were rapidly fatal. On the upside, population density was incredibly less meaning far, far fewer communicable diseases like smallpox, measles, and flu. Most likely causes of death were accident or illness, which might well arise from accident (think infected wounds).
If you survived to adulthood you were likely to survive into at least middle age. Despite a lack of medical care, adult hunter-gatherers usually survived into their 40’s and living into the 60’s was fairly common. It was the under 20 crowd that died a lot and drove down the average lifespan.
A woman needed only two surviving-to-reproduce children to maintain the population, and 3 children per women (on average) surviving to reproduce would result in population growth. Assuming she started having kids at 20 and had one every 5 years until 45 (conservative and rounded off for convenience) that would be 5 pregnancies per women. If only two survived to adulthood - that’s a 60% fatality rate! - it would still be enough to maintain the population and if three survive (40% death rate) then the population grows over time.
So, a human population can sustain a far higher death rate than we currently have and yet continue to exist.
Certain things occur in all primates (and to some extent in all mammals) as they mature, and by noting those milestones you can have an idea of both age at death and typical age of sexual maturity. It is far from exact, but can give a rough idea. The biggest obstacle to doing this systematically is a lack of suitable skeletons to analyse. You need things like teeth (eruption of various teeth indicate age, and the wisdom teeth coming in signify physical maturity), skulls (the state of the “sutures” between the bones of the skull indicate age), and the ends of long bones (their condition likewise can signal things like maturity and advanced age). Most fossils of early humans are teeth or fragments of jawbones and skulls. That’s why fossils with significant other bones are so very important.
For pre-literate settlements you can analyse burials, if you have enough, to get decent information on age of death/life expectancy for that community though, as noted, you will almost certainly lack information on infanticide.
The fact that breast-feeding doesn’t guarantee a lack of new baby accounts for some infanticide practices.
Certain customs come up again and again in pre-agricultural or semi-agricultural communities that act to space out children. Remember, for a hunter-gatherer woman having another child too soon can doom both children. Customs to prevent a mother having two under two (so to speak) are:
Killing all but one child if a multiple birth occurs
Killing a child born while a woman is still breast-feeding another child
Killing children if they can’t be promised a spouse at or near the time of birth (arranged marriages are very common in such societies which can have extremely complex and taboo-ridden kinship systems)
Killing any child presenting a defect at birth
If food shortages occur, killing/neglecting to death a child to better give resources to other children (a LOT of animals do this, from mammals to birds)
Taboos on having sex with a breast-feeding woman (gotta admit, abstinence is pretty darn effective birth control)
These are all pretty damn harsh by our standards, actually criminal by our standards, but hunter-gatherers lived under vastly different conditions than we do and much of the above was for survival reasons.
Because hunter-gatherers were typically as active as modern elite athletes in order to survive and food sources scattered and sometimes scare, frank starvation was probably rare but times of low food resources sufficient to impair fertility probably did occur more than once in a woman’s lifetime.
For a woman under such conditions, breast-feeding might reduce fertility more than it would for a less active woman with more plentiful food supplies. Women’s bodies are attuned to fat reserves and they are a major factor in fertility. When they drops below a certain point women don’t conceive. Consider that highly competitive female athletes in the modern world may stop menstruating despite food more abundant than any other time in history - dropping her body fat that low was much more likely for the average hunter-gatherer woman than for the average woman today. If she had just sufficient reserves to conceive, bear, and breast-feed one child it MIGHT be that her body was less likely to conceive another than if she had greater fat reserves. Consider that a hypothesis rather than any sort of proven fact.
It’s not enough to just “have lots of babies”, those babies have to survive long enough to reproduce. The numbers are a little fuzzy, but early agriculturalists tended to have babies 2-3 years apart, and surviving groups of hunter-gatherers tended to have babies about 5 years apart (basically, no new infants until the prior child was reliably self-mobile and able to eat the same food as adults as their sole diet). Hunter-gatherers almost invariably have no surviving twins… but since they’re the same sort of human as the rest of us, something has to be happening to the twins. It’s a pretty good guess they kill any babies in excess of 1 that occur at a birth. That’s what it takes to raise a child to adulthood - 5 year spacing and no multiples - in that setting.
Some items I read mentioned that women having regular periods, high birth rate, etc - was somewhat of a modern phenomenon. Poor nutrition, breastfeeding, etc. tended to reduce ovulation and the number of pregnancies.
Plus there’s the suggestion that high infant mortality is the result of crowding that comes with agriculture; plus we get many of our diseases from domesticated animals, so hunter-gatherer groups from more than 12,000 years ago would not typically have the critical mass or sources for a lot of diseases.
The statistic is completely made up, as we have almost no data about 50,000 years ago, certainly not enough to speculate on birth rates or infant mortality. More likely, someone is projecting modern subsistence agricultural third-world numbers onto a hunter-gatherer social structure.
As for statistics… the average human has one breast and one testicle. Averages don’t always tell the whole story.
You’re right. I did forget to explicitly say that equal numbers died at both ages. But as you can see from the numbers I subsequently used, that was one of the assumptions I was acting on.
Most “how effective” stats are usually collected by asking a large number of couples to participate in a study, or by surveys of couples who have used a type of contraception.
Most “effectiveness” failure stats reflect real-world issues like remembering to take pills, whether a condom is missed or used incorrectly due to excessive alcohol consumption.
I assume “theoretical effectiveness” is measured by asking, in the survey, if a pill was missed - and if so, eliminating that person from the stats.
But in this population of 50% dieing at 1 and 50% at 19, your life expectancy at age 2 is exactly 17. Not accounting for this is I think why the OP is confused. (Welcome to the Dope, by the way.)
For example, the life expectancy of Golden Retrievers is 9. Mine is 11. She wags a lot for a dog dead for 2 years.
BBC and Wikipedia are not scientific journals. I meant a cite for a study that comes to that conclusion (the Haub paper just repeats the figure from elsewhere,and has crappy citation itself, it doesn’t present it as its own study)
Female infanticide was another factor contributing to women’s scarcity and male competition. Although the number of male and female babies should be nearly equal at … surveys of hundreds of different communities from over a hundred different cultures … has shown that juvenile sex ratios averaged 127:100 in favour of the boys, with an even higher rate in some societies …
The Eskimos …registered childhood sex ratios of 150:100 and even 200:100 in favour of the boys….
Australian Aboriginal tribes childhood ratios of 125:100 and even 138:100 in favour of the boys were recorded …
childhood boy ratio to every 100 girls was recorded to be: 140, 124… 143… 133…. 160 .Although the evidence is naturally weaker, similar ratios in favour of the males have been found among the skeletons of adult Middle and Upper Palaeolithic hunter-gatherers, indicating a similar practice of female infanticide that may go back hundreds of thousands of years
Food shortage was vastly *more *of a problem in non-HG groups. The chances of a HG dying of malnutrition and complications was about 1 in 100. For pre-reformation agriculturalists about 1 in 5. All human groups expand to maximally exploit the food available. HGs tend to reach that maximum at lowers densities and stabilise it through population control. Agriculturalists tend to reach it at higher levels and the population is unstable and experiences boos and busts.
Of course shortage of food isn’t really a factor in infanticide. Most societies didn’t see much, if any, distinction between infanticide and abortion. The modern US has no food shortages at all, and yet about a million of abortions each year even with freely available 99% birth control. Ancient societies practiced infanticide for *exactly *the same reasons *and *added food shortage to the reasons *and *had no effective birth control. So most infanticide was done simply for lifestyle reasons, just like most current abortions. People thought they were too young to have children, they weren’t financially secure, it would disrupt their ability to marry well, the child would reduce their standard of living and so forth. To which we can add, “the child was the wrong sex” and “there just ain’t enough food” which are uncommon in the modern US.
Infanticide was so common that it was mentioned as casually as taking clothes to the dry cleaners.
