CARTA: Evolutionary Changes in Human Birth Spacing
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- Опубліковано 26 гру 2023
- Life history theory suggests that inter-birth intervals (IBIs) depend on a trade-off between maternal investment in current and future offspring, influenced by the mother's energy and somatic maintenance. Normally, IBI aligns with maternal and infant body size, larger relative infant size leading to slower breeding. In contrast, humans have relatively shorter IBIs due to cooperative breeding, support from the social group. Some other species with cooperative behaviors also exhibit shorter IBIs, possibly aided by factors like meat-eating enabling early weaning around 2.5 million years ago in the Homo lineage. [1/2024] [Show ID: 39276]
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Building on the argument for additional resources we might be able to explain the reproductive success of certain high resource I.e. aristocratic families where there were large numbers of surviving children on the use of wet nurses and nannys which took most of the energetic burden off the high status wife.
Reminds me of a book that was an important resource when I was a grad student in anthropology the 70s -- Roy Rappaport's "Pigs for the Ancestors," which documents conscious and carefully callibrated manipulation (socially regulated distribution) of the energy available from high quality food sources to different segments according to differential, and changing needs among hunter-gathers-farmers in highland Papua New Guinea.
I have two children, eight years apart. I was trying for ten years between them. Thankfully, I live in an area where I was able to plan my family.
Makes you wonder though - I know human fertility is on the downslide because of social reasons, but might we also inadvertently also be reverting to a longer IBI? We have less of that alloparenting happening as the older generation is having to work more and is less interested in helping care for children (a lot of millenials complain about this, myself included), and our food is apparently becoming less nutritionally dense.
I will say that I got shocked responses at the beginning of my 2nd and 3rd pregnancies when I was asked when I weaned my children and informed them that I was still nursing them. I nursed my 1st and 2nd child most of the way through the subsequent pregnancy in fact, and only weaned them because it was beginning to hurt too much for me to continue.
Fascinating!
The most important question to ask is - why didn't any of the other great apes, lesser apes or other animals use the same strategy?
The point is you can't just acquire a bigger/smarter/cooperative brain simply because you need one. Irrespective of its ultimate potential, to endure, every step of encephalization, which only occurs courtesy of natural variation, must be energetically balanced by the immediate environment, not future possibilties. Basically, 'natural selection' can only 'select' from that which already exists. The obvious implication being, you can't use the 'behaviours' or 'intellect' provided by a large brain, in order to accumulate the energy required to support a large brain, before you first get that large brain. To get large/r brains to endure and spread, not selectively, but stochastically, through both the population and future generations there must first be sufficient excess energy to support greater general variation. Otherwise, if along the way, you put your extra energy into a larger cooperative brain, but your neighbours put their extra energy into reproduction, then your cleverness will inevitably dissipate and disappear into the wider community.
Quite right. Large brain; bipedal; speaking; hairlessness; relatively immature babies; so many factors CARTA is or should be concerned with, cannot be dealt with by just so reasoning.
I mean our brains have developed over hundreds of thousands if not millions of years to be much bigger than those of other apes, so it’s been a very slow process with most likely immeasurably small differences looking at only a few successive generations at a time that wouldn’t require a noticeable amount of increased caloric intake for that marginal benefit to pay off. Additionally, humans do have slower metabolisms for our body weight which may have something to do with this problem you mentioned.
There's a very obvious answer that every paleoanthropologist will tell you: Fire and meat. The shift from small bodied Homo habilis to large bodies Homo eregaster/erectus marks the introduction of fire and cooked meat. This is the "high-quality, nutrient-dense and difficult-to-acquire" food mentioned in the talk. This gave the energy surplus to allow for a large brain. Large body size means hard births since we're standing upright, which again make females more choosy of males likely to offer support, which again apparently favored larger brains. Take a stroll down to the local single's bar, and you'll see the evolutionary trend still being in action.
Very interesting, thank you
Okay, the average female body size is inaccurate, at least for a modern population. The lowest mean body size I could find was still above the 55 kg mark. Is this in ancestral populations? If so, you should indicate that in your slides.
I'm 43kg
Later in the lecture, when she's talking about the inter birth intervals, she says that the data is from hunter gatherer populations. Hunting and gathering means a lot fewer calories than the average person in a modern population
She literally spells it out on a slide... including explaining that industrial countries have shorter intervals than hunter-gatherer populations.
No matter the availability of other food, breastfeeding is still the best food for human infants.
Very nice information that I love ! Thank you for sharing it with pleasure . If you know well that , the origin of humen had been from animals , you must know the origins of animals , birds fishes etc. that , they existed on earth too . Happy Friday to you !
I breastfeed during both of my pregnancies. I have no idea where you got your information about that!!! My son did self wean when I became pregnant because the the taste changed but, my daughter had no problem continuing to nurse. I still nursed her in tandem with my youngest. They all did self wean at age 3 but I got my period back after about 18 months.
Everyone is different. I got my period back 4/5 weeks after my c-section, even though I was still recovering from birth.
That’s not the statistical norm thou. Everyone in the modern world has significant impacts- she is talking about general scientific changes not an individual choices.
Very interesting, especially the Baboon IBI changes. It's amazing that we have such large brains, and yet we cannot see or openly deny our destruction of the planet and exploitation of other species and each other. Most cannot contemplate the need for sustainability, let alone its most basic parameters. How is this possible? What is this big brain doing?
It seems that by developing sophisticated tools to manage my time, and to be conscious of every microseconds of my existence I am also capable of stretching space a.k.a. my mind can be present at any location in the universe at my will.
This is very interesting observation. I will continue practicing this crazy freaky state of mind and see what happens next.
😮😊
Amadeus Mozart is describing to the emperor of the Habsburg empire of the time, a phenomena of a human mind today in linguistics. We understand how it is happening, but from metaphysical point of you, it can be explained like this. Everyone is having original ideas and everyone is arguing his righteousness, but everyone is dancing to the same music
In other words, the functions of the universe are appropriately tuned to our size, regardless of our personal preferences
So it seems that personal choice, or even “the will” yes, “personal will” is irrelevant
😮😢🎉
If humans are said to come from apes where did apes originate ?
Apes split off from other primates about 25 million years ago. Primates began to diverge from other mammals about 70 million years ago. Mammals seperated from other animals about 180 million years ago