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Thread: Did our early births make us smarter?

  1. #1 Did our early births make us smarter? 
    Administrator KALSTER's Avatar
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    Humans are born at an earlier developmental stage than other mammals as a result of our narrow pelvises, required for upright locomotion, or the babies head won’t fit. How does this influence the way we function in the world? Every animal is born with a certain set of innate abilities, or instincts. I am wondering if our early births could have negatively affected the amount of innate abilities we are born with, inadvertedly forcing us to become more flexible, as a result of the ratio between learned and innate abilities increasingly being shifted more in favour of learned abilities. We would become more flexible, since the larger amount of learned information is directly affected by the surroundings we grow up in. A brain that is able to learn better at a young age would endow the individual with an advantage, as his set of learned abilities would be superior to his peers, increasing the chance of survival.

    I have read that humans display a certain level of neoteny, i.e. we tend to carry some of our juvenile attributes into adulthood. One of these attributes could then be an increased ability to learn?

    Could this shift to an upright mode, also freeing our hands in the process, then be a pivotal step responsible for our current success as far as our brain dynamics go?


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    Forum Cosmic Wizard paralith's Avatar
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    From what I understand, there are really two things at work when it comes to us humans and our brains.

    First and foremost is that, without the particularly rich diet that we evolved to take advantage of, we would not have been able to evolve the adult brain size that we have. We're way above the regression line when it comes to expected brain size according to our body size, even for primates, and a brain that big requires a diet far more rich than one consisting primarily of fruit and the occasional colobus monkey. On the flip side, without a brain as complex as the one we have, we probably would not be able to eat the foods we do, ie hunting other large animals. Brain size and diet probably coevolved together over the course of human evolution.

    Secondly is the issue of brain size at birth. Since the human female birth canal is so small, a human infant simply cannot grow its brain to adult size while still in the womb. An infant monkey has a brain size that is about 70% of adult brain size - an infant human is about 30%. It takes 7 years to grow our brains to adult size. But that means that during those seven years, instead of being confined semi-conscious inside a womb, you're exposed to the environment, and that allows your brain to develop in response to that environment, instead of according only to preset rules in the genome.

    I'm inclined to say that this isn't a specifically evolved response, but rather a side-effect of bipedalism and particularly large adult brain size that was then co-opted for an adaptive purpose. (As an interesting side note, I do think something similar actually is a specifically evolved response in monkeys, but I won't go into it here unless anyone is curious.)

    I'm not sure I think that learning is a neotonous trait; I think that's more tied to our brain size and complexity, especially considering that when you're an adult your brain isn't still growing and developing the way it was when you were younger than 7. Usually the neotony theory is thrown out there to explain our increased sociability and our decreased (relatively) aggression. Some researchers think bonobos are neotonized chimpanzees for the same reasons.

    I personally think increased sociability is another co-evolved trait with our intelligence and our diet. Hunting larger game in particular requires a high degree of cooperation - good cooperation requires good social skills, and good social skills take up brain space. Remembering and identifying every one of 150 or more individuals, knowing all their friends and relatives, knowing their skills and who's a good hunter and who isn't, knowing their personalities and who's a good sharer and who isn't, etc etc - that's not easy stuff to keep straight, but we humans do it as easily as we breathe. And if aggression towards members of your own species does not advance your reproductive success, which it would not if cooperation is so important, then it makes sense that we'd also evolve to be less aggressive - at least with members of our own group.


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  4. #3 Re: Did our early births make us smarter? 
    Forum Cosmic Wizard spuriousmonkey's Avatar
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    Quote Originally Posted by KALSTER
    Humans are born at an earlier developmental stage than other mammals as a result of our narrow pelvises, required for upright locomotion, or the babies head won’t fit.
    Not totally true of course. Some development is accelerated, some is delayed. This is typical for all 'modified' animals. The accelerating and delay is of course dependend on what you take as a baseline.

    In other words developmental shift is a normal occurrence and not something special.

    Our lungs aren't delayed developmentally for instance. They can't be. Otherwise you can't breath.

    Chinchillas have accelerated hair development. They are born with fur.

    So to repeat the main point one more time: variation in developmental timing is normal and varies within the animal. Different processes develop at different speeds, depending on the need and what you take as a baseline.

    Back to the original question. Let me reformulate it:

    Are we smarter because we have narrow pelvises.

    No. We don't have narrow pelvises. Our pelvises are rather normal. It's the baby's head that is large.

    We are smart because we have a big brain.

    No surprising answers here.
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  5. #4 Re: Did our early births make us smarter? 
    Forum Cosmic Wizard paralith's Avatar
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    Quote Originally Posted by spuriousmonkey
    No. We don't have narrow pelvises. Our pelvises are rather normal. It's the baby's head that is large.
    But human female pelvises are probably narrower than would be expected according to infant skull diameter at birth, thanks to the constraints placed on them by bipedalism. Normal is relative.
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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  6. #5 Re: Did our early births make us smarter? 
    Forum Cosmic Wizard spuriousmonkey's Avatar
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    Quote Originally Posted by paralith
    Quote Originally Posted by spuriousmonkey
    No. We don't have narrow pelvises. Our pelvises are rather normal. It's the baby's head that is large.
    But human female pelvises are probably narrower than would be expected according to infant skull diameter at birth, thanks to the constraints placed on them by bipedalism. Normal is relative.
    Indeed...according to infant skull diameters. And what has increased rapidly during hominid evolution?

    The skull/brain size.

    There was bipedalism before large brains. (large as in our large).

    Hence bipedalism was never the constraining factor. It's the increase of the brain that met a hip constraint about only 100.000 years ago. Before that it wasn't really a limiting factor.

    So it isn't the narrow hips. It is the enlarged skull that made us smart. It's not as if our brains actually grow after birth. They mainly die, cull the undesirable links and cells. What happens mostly after birth is the final selection in wiring of the brain.

    What seems to be really unique to humans is the growth spurt during juvenile life. There seem to be at least two actually. Puberty and I can't remember exactly, but it is either at 6 or 8 years.

    Either way, narrow hips didn't make us smarter. The large skull just required we were born sooner than the baseline.

    Large brains needed longer learning time, so extension of the juvenile phase. What comes first? Chicken or the egg?

    Did change in developmental timing make us smarter? Or is did developmental timing change because we became smarter?

    I am going for the last one pure for didactic reasons.
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