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BadgerSilver t1_iv0020i wrote

Reply to comment by DumbDekuKid in How many children did Homo Erectus tend to have? by [deleted]

This has to be due to infant mortality. I can't imagine they weren't just having sex and getting pregnant whenever they could

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muskytortoise t1_iv0dzxx wrote

Humans are somewhat unique in that we can have children at any time of the year. Pregnancy and live children cause hormonal and social behaviours reducing chances of another conception for a time - pregnancy and feeding are both very energy intensive. Infant and child mortality tends to be about 50% for most ancient humans, apes and most large mammals with some exceptions. 6 children over a lifetime is about the replacement rate with those numbers, and most populations tend to keep at mostly a steady population level otherwise they would run out of resources. Given that they did not outcompete humans by their sheer numbers, about replacement rate sounds like a very reasonable assumption to make.

So what exactly are you basing your assumption off of?

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alderhill t1_iv0knc3 wrote

I don't think it's clear that homo sapiens and homo erectus overlapped, and if so, we certainly do not know about all locations.

H. Erectus did stick around for a long time, even as new homo species branched off, but my understanding was the evidence for overlap is slim outside of Africa. Maybe Indonesia, but I've seen conflicting evidence.

In any case, they were mostly already on their way out by the time we started showing up in numbers.

Neanderthals and Denisovans of course did overlap with us in some regions.

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AChristianAnarchist t1_iv0myet wrote

The evidence for overlap outside africa is pretty overwhelming actually. There have been more examples of this overlap found in the middle east and asia than in Africa.

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muskytortoise t1_iv0oxp2 wrote

While you are absolutely right to point it out I didn't mean they were directly competing with humans but rather pointing out that constant breeding much above replacement rate would allow them to outcompete other groups. Since tendencies describe averages, if they had more than 6 children at the typical 50% mortality rate it would cause the population to grow fairly fast. Of course that comment probably stemmed from greatly overblown idea of infant mortality that person has.

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alderhill t1_iv0qkir wrote

OK cool, yea, I got that point, just was a bit confused about the context of homo erectus. I agree, though. It seems biologically, primates just generally aren't super-breeders.

IIRC, earlier homonids probably came to breeding age quicker than we do (under depending on nutrition, etc)., so a Homo erectus female of 10 years may have already been in prime mothering age. A child every 2-3 years or so would mean that by age 30, she'd possibly be a grandmother and done with most child rearing.

I do agree as well that mortality rates are on average overblown... once they pass the first two or so tough years, their odds are much improved

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BadgerSilver t1_iv7m3wu wrote

Humans will have babies every 1-2 years consistently if fertile with unprotected intercourse. Are you saying homo erectus is that different?

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The_Dread_Salami t1_iv0j105 wrote

It's also possible they had a breeding season i mean most babies now are concieved between june and November as is. Then there's the fact that jealous males in other species kill any child they don't think is there's, this may also be a contributing factor.

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mcr1974 t1_iv0lbf3 wrote

September is the month with most births, which would suggest most conception takes place in December?

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The_Dread_Salami t1_iv0ns7m wrote

It's too cold to hunt very often aside from big game that'll keep because of the cold which left plenty of time to "keep warm" so I can easily see this being accurate for our early ancestors too.

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atomfullerene t1_iv2ujtg wrote

Birth spacing in hunter gatherers is 3-4 years, and it's the same or higher in great apes. Generally speaking, they all tend not to get pregnant while still nursing the previous offspring.

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BadgerSilver t1_iv7k5hg wrote

I don't believe it, we're no different from hunter gatherers in capability of having yearly offspring. In religious communities where I grew up, most families had kids spaced ~2 years apart, and they had access to birth control. Nursing hormones don't outright block pregnancy for 4 years. I bet we can find a study

edit: from the NHS "Most couples will get pregnant within a year if they have regular sex and don't use contraception". We can safely assume this applies to hunter gatherers. This 4 year thing is absurd.

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atomfullerene t1_iv7u0u2 wrote

Nursing frequency and birth spacing in Kung hunter-gatherers

citation for long birth intervals in !Kung

Foraging and Menstruation in the Hadza of Tanzania

citation for shorter, but still 2.5 yr birth intervals for Hazda

Analysis of Factors Involved in Lactational Amenorrhea

citation for big variation in how long infertility lasts during nursing, depending on specific situation...in other words, you can't safely assume that the same thing applies to people with totally different nursing habits and totally different nutritional profiles.

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