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Thread: brain shrinkage

  1. #1 brain shrinkage 
    WYSIWYG Moderator marnixR's Avatar
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    in Matt Ridley's "Nature via nurture" i read that :

    In the Mesolithic (around 50,000 years ago) human brains averaged 1,468cc (in females) and 1,567cc (in males). Today the numbers have fallen to 1,210cc and 1,248, and even allowing for some reduction in body height, this seems to be a steep decline

    does anyone know the original source of this statement + how secure are the figures (especially what was the sample size) ?

    btw, these figures are put forward as an example of self-domestication in humans - is this accepted theory or fringe ?


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    Forum Cosmic Wizard paralith's Avatar
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    I don't know the original source, but in my anthropology lectures on human evolution I definitely remember hearing that modern humans actually have smaller average brain sizes than earlier humans. I've never heard of the self-domestication theory, though if I were to hazard a guess, I'd say perhaps our brains have simply become more efficient. A brain is a costly organ to maintain, so it would be advantageous to evolve more complex neural structures that require less physical mass and therefore less resources.


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    WYSIWYG Moderator marnixR's Avatar
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    i just wonder - we presumably became shorter near the time agriculture was adopted, and larger populations actually introduced a less healthy lifestyle than the mesolithic hunter-gatherers

    as you said the shrinkage of the brain, being a more costly organ to maintain, might just be a more extreme response to the diet becoming less nutritious and varied

    on the other hand, it is well-known that domesticated animals have smaller brains than their wild counterparts because they don't have to fend for themselves - the self-domestication theory would imply that brain shrinkage in humans coincides with society's protection against the hardships of natural selection
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    Forum Professor sunshinewarrior's Avatar
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    Quote Originally Posted by marnixR
    on the other hand, it is well-known that domesticated animals have smaller brains than their wild counterparts because they don't have to fend for themselves - the self-domestication theory would imply that brain shrinkage in humans coincides with society's protection against the hardships of natural selection
    Wouldn't we, though, see that this shrinkage did not take place in populations that were isolated from agriculture (it being a relatively recent phenomenon - 15000 years or so)? That is, Tasmanians (and probably most original Australians), large numbers of New Guinean peoples, and many populations in the Brazilian rain-forests would never have been self-domesticated. I have never heard that such significant sounding differences were noted - though it would have been a lovely one in the eye for the racists claiming that 'savages' were less evolved!
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    Forum Cosmic Wizard paralith's Avatar
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    Quote Originally Posted by sunshinewarrio
    Quote Originally Posted by marnixR
    on the other hand, it is well-known that domesticated animals have smaller brains than their wild counterparts because they don't have to fend for themselves - the self-domestication theory would imply that brain shrinkage in humans coincides with society's protection against the hardships of natural selection
    Wouldn't we, though, see that this shrinkage did not take place in populations that were isolated from agriculture (it being a relatively recent phenomenon - 15000 years or so)? That is, Tasmanians (and probably most original Australians), large numbers of New Guinean peoples, and many populations in the Brazilian rain-forests would never have been self-domesticated. I have never heard that such significant sounding differences were noted - though it would have been a lovely one in the eye for the racists claiming that 'savages' were less evolved!
    Haha, yea, less evolved - with BIGGER brains! It might be a tough sell

    But that's a really good point, shanks. A comparison with non-agricultural groups would be really edifying. And conversely, it would also be interesting to compare the brain:body size between domesticated pigs, wild pigs - and maybe even domesticated pigs gone feral. They do exhibit pretty dramatic physical changes in a short period of time - though I guess it would be unlikely that their skulls could loosen up to allow for bigger brains
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    WYSIWYG Moderator marnixR's Avatar
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    Quote Originally Posted by paralith
    But that's a really good point, shanks. A comparison with non-agricultural groups would be really edifying.
    does anyone know whether any such data are available, or whether any such study has been carried out ?
    SJ Gould's "Mismeasure of man" is now fairly old + i don't remember anything relevant mentioned there
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    I thought this was true of Homo Neanderthalis which is though to be a different species to homo sapiens . Are you sure youre not confusing it with them?
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    WYSIWYG Moderator marnixR's Avatar
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    positive - we're talking mesolithic here, way past the point where neanderthals became extinct
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    50,000 years sounds like a very short period of time for that to happen.
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    Forum Cosmic Wizard paralith's Avatar
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    If there's a strong enough selective force at play, it could happen.
    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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    WYSIWYG Moderator marnixR's Avatar
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    Quote Originally Posted by Robbie
    50,000 years sounds like a very short period of time for that to happen.
    forget 50,000 years - the mesolithic ended sometime between 15,000 and 10,000 years ago
    and no, i don't have a problem with these time scales
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    Forum Cosmic Wizard spuriousmonkey's Avatar
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    There have been studies that showed rapid genetic evolution of the brain in the last 10,000 years, so the time scale is quite feasible.

    Can't be arsed to look them up. They have been posted in threads in this subforum.
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    Marnix, FWIW, I have heard competing theories with the bigger=more evoled/smarter theory, but cannot find the papers at the mo. IIRC, at least one group speculates that brains did become larger with evolution, but that they have also become smaller more recently, without loss of intelligence.

    I did find one item that I had not seen before. It is not directly relevant, but may be of interest.

    Specifically, we found that as the distance from the equator increased, north or south, so did brain size."
    The researchers are tying brain size to climate, in this work.

    http://www.albany.edu/campusnews/releases_286.htm
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  15. #14  
    Forum Cosmic Wizard paralith's Avatar
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    From what I understand of the importance of brain size, there is a general trend of larger brain:body ratio correlating with greater intelligence, but when it comes to fine differences (such as between individuals of the same species, or between closely related species), it's structure that's more important. That's kind of what I was trying to get at by suggesting that a reduction in brain size would be advantageous because it reduces the resource load required for the brain, but that it was offset by more complex neural structures so that our overall intelligence did not decrease significantly.
    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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