How did early humans reproduce with a low life expectency?

[Aspidistra]

@Broomstick

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.

That all supports the “40% infant mortality by age 1” stat, which I think people aren’t having so much of a problem with - but doesn’t really help with the “average age of 10” stat (which, for all I know, you may not even be wanting to support ;)).

If the above is a profile of the average woman, and men live roughly as long, then even if you assume the average woman dies straight after the last kid, and kill off all the number 3 kids at age 1, you still end up with an average life expectancy of 18.

In order to get the number down to 10, you have to have even your adults - the ones reaching reproductive age and giving birth to/siring an average of 5 kids - dying on average at around 25. That seems to be pushing the envelope somewhat.

[slash2k]

@Aspidistra

In order to get the number down to 10, you have to have even your adults - the ones reaching reproductive age and giving birth to/siring an average of 5 kids - dying on average at around 25. That seems to be pushing the envelope somewhat.

Not necessarily. Death in childbirth was pretty common even up until fairly modern times–in Britain in the 1870s/80s, e.g., there were about 60 maternal deaths per 1000 births. For the early modern period, I’ve seen estimates that a woman’s risk of dying in childbed was about one to two percent per pregnancy, and I suspect it may have been even higher in prehistory.

[Aspidistra]

@slash2k

Not necessarily. Death in childbirth was pretty common even up until fairly modern times–in Britain in the 1870s/80s, e.g., there were about 60 maternal deaths per 1000 births. For the early modern period, I’ve seen estimates that a woman’s risk of dying in childbed was about one to two percent per pregnancy, and I suspect it may have been even higher in prehistory.

The problem is not just dying on average before 25, it’s that and having on average 5 born kids per woman (not counting miscarriages, which take up breeding time, and don’t add to your born kids stat). Either by themselves is fine - both start to strain credulity.

And ages with high death in childbearing rates also tend to have high death in childhood rates - not just among the 0 year olds, but subsequently. A bunch of dying 10, 11, 12 and 13-year olds, too young to help with population replacement but old enough to be pushing the average death age up, is really going to bugger up the “average death at 10” stat

[Broomstick]

@Aspidistra

That all supports the “40% infant mortality by age 1” stat, which I think people aren’t having so much of a problem with - but doesn’t really help with the “average age of 10” stat (which, for all I know, you may not even be wanting to support ;)).

Nope, not standing with the “average age of 10” statement, which isn’t mine and strikes me as too low.

@Aspidistra

If the above is a profile of the average woman, and men live roughly as long, then even if you assume the average woman dies straight after the last kid, and kill off all the number 3 kids at age 1, you still end up with an average life expectancy of 18.

The average women is NOT dying straight after the last kid - grandmothers are a significant source of food and childcare in recent H-G societies, and would have been even more important in the past prior to the H-G’s being able to acquire things like metal tools from non-H-G’s nearby,

In order to get the number down to 10, you have to have even your adults - the ones reaching reproductive age and giving birth to/siring an average of 5 kids - dying on average at around 25. That seems to be pushing the envelope somewhat.

You’re going to have a significant death rate among adults due to lack of anything we’d call medical care, hunting accidents for the men, childbirth gone wrong in women, predators, and accidents doing all the other things in life: cuts/punctures, burns, etc.

@slash2k

Not necessarily. Death in childbirth was pretty common even up until fairly modern times–in Britain in the 1870s/80s, e.g., there were about 60 maternal deaths per 1000 births. For the early modern period, I’ve seen estimates that a woman’s risk of dying in childbed was about one to two percent per pregnancy, and I suspect it may have been even higher in prehistory.

Gotta remember that in the 19th Century a major source of post-childbirth death in new mothers was the doctors, who spread childbed fever due to lack of handwashing.

HG women do sometimes die in childbirth, but they avoided doctor-spread infections and due to their lifestyle in general were pretty strong, healthy women. Stats on death in childbirth for them are all over and pretty much pure speculation.

[John_Mace]

@MrDibble

For those without SpringerLink access, Google Books also has that section available.

I still can’t access anything on that link, either.

Maybe someone who has access can quote the part that confirms that “It’s pretty well established that infanticide was the norm amongst HG”. I don’t doubt that some groups practiced infanticide, but I’m unclear that the consensus is that most did.

[slash2k]

@John_Mace

I still can’t access anything on that link, either.

Maybe someone who has access can quote the part that confirms that “It’s pretty well established that infanticide was the norm amongst HG”. I don’t doubt that some groups practiced infanticide, but I’m unclear that the consensus is that most did.

The relevant paragraph is:

Polygyny greatly exacerbated women’s scarcity and direct and indirect male competition and conflict over them. Indeed, a cross-cultural study has found polygyny to be one of the most distinctive correlates that there is of feuding and internal warfare. [46] There is another factor contributing to women’s scarcity and male competition. In all hunter-gatherer (and agricultural) societies, female infanticide is regularly practiced. Parents prefer boys who can hunt (or work in the fields) and protect. Infanticide is often covert and attributed to accidents, but census statistics of pre-industrial societies tell an unmistakable story. Although the number of male and female babies should be nearly equal at birth (105:100 in favour of boys), there are many more boys in childhood. Surveys of hundreds of different communities from over 100 different cultures (of which about a fifth were hunter-gatherers) has shown that juvenile sex rations averaged 127:100 in favour of boys, with an even higher rate in some societies. The Eskimos are one of the most extreme cases. Their harsh environment made them wholly dependent on male hunting, whereas female foraging played a greater economic role in milder climates. Thus female infanticide was particularly widespread among them. They registered childhood sex rations of 150:100 and even 200:100 in favour of boys. No wonder then that the Eskimos experienced such a high homicide rate over women, even though polygyny barely existed among them. Among Australian Aboriginal tribes childhood ratios of 125:100 and even 138:100 in favour of boys were recorded. The Orinoco and Amazonian basin hunters and horti-culturalists have been closely studied. Their childhood boy ratio to every 100 girls is: Yanomamo 129 (140 for the first two years of life), Xavante 124, Peruvian Cashinahua 148. In Fiji the figure was 133. In tribal Montenegro it was estimated at 160. Although the evidence is naturally weaker, similar ratios in favour of males have been found among the skeletons of adult Middle and Upper Paleolithic hunter-gatherers, indicating a similar practice of female infanticide that may go back hundreds of thousands of years.[47]

Unfortunately the Google Books excerpt is incomplete and does not include the footnotes.