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Thread: The Brain between Species and between Humans?

  1. #1 The Brain between Species and between Humans? 
    Forum Masters Degree Golkarian's Avatar
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    Brain size to body size ratio seems to have an effect between species but not between two individual humans. Any thoughts as to why this is? I personally think it might be because the human brain is so large that complexity and random non-heritable change might be responsible for higher intelligence, whereas other species don't have the capacity for this complexity, but that's only a guess. What do you think?


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  3. #2 Re: The Brain between Species and between Humans? 
    Forum Cosmic Wizard paralith's Avatar
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    Quote Originally Posted by Golkarian
    Brain size to body size ratio seems to have an effect between species but not between two individual humans. Any thoughts as to why this is? I personally think it might be because the human brain is so large that complexity and random non-heritable change might be responsible for higher intelligence, whereas other species don't have the capacity for this complexity, but that's only a guess. What do you think?
    There is growing evidence that a significant amount of the variation in human intelligence is in fact heritable. I would suggest reading this paper:Neurobiology of Intelligence: Science and Ethics.


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  4. #3 Re: The Brain between Species and between Humans? 
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    Quote Originally Posted by Golkarian
    Brain size to body size ratio seems to have an effect between species but not between two individual humans. Any thoughts as to why this is? I personally think it might be because the human brain is so large that complexity and random non-heritable change might be responsible for higher intelligence, whereas other species don't have the capacity for this complexity, but that's only a guess. What do you think?
    I suspect that the differences in body/brain size between species are much bigger than the differences between members of the same species.
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    Administrator KALSTER's Avatar
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    If I remember correctly, there is a direct relation between brain size and body size that is determined by the number of body cells the brains has to service in terms of the most basic bodily processes (procreation and feeding) and then any additional brain function developed towards making sense of sensory data and reacting to it, building up programmed responses and then finally a development towards more control of everything, with the "cleverness" of an organism depending on how encompassing, adaptable and developed these processes are. Is this loosely accurate? I probably forgot a big chunk of it, or misremembered it completely. :?
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  6. #5  
    Forum Cosmic Wizard paralith's Avatar
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    Quote Originally Posted by KALSTER
    If I remember correctly, there is a direct relation between brain size and body size that is determined by the number of body cells the brains has to service in terms of the most basic bodily processes (procreation and feeding) and then any additional brain function developed towards making sense of sensory data and reacting to it, building up programmed responses and then finally a development towards more control of everything, with the "cleverness" of an organism depending on how encompassing, adaptable and developed these processes are. Is this loosely accurate? I probably forgot a big chunk of it, or misremembered it completely. :?
    I think Golkarian means differences in brain size relative to body size; thus, differences that are not solely due to scaling.
    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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    Administrator KALSTER's Avatar
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    I was trying to say in my customarily unclear fashion that one could predict a baseline of what minimum level of cephalisation would be required for an organism that falls within a predetermined Phylum or Class. The levels of cephalisation above this baseline would then, roughly, indicate "cleverness". Is this true or did I recall a false memory? :wink:
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    If I understand correctly, your question regards the variance of species intelligence relative to brain size. I don't think brain size is a reliable determinant of relative intelligence given the comparative evidence between modern man and his extinct competitor, Neanderthal. The Neanderthal brain was of equal or larger size than contemporary humans and genetic evidence suggests they may even have had language. Other evidence suggests that Neanderthal may also have had culture and religion. However, their long history and lack of significant innovations relative to those of modern humans suggest to me a lower intelligence. From the research I’ve reviewed, brains size is merely a determinant of experience and diet rather than intelligence. In my view, the equal or greater brain size of the Neanderthals to the modern humans of their era suggests their equal experience and diet rather than intelligence.

    In some species, experience may equate intelligence. Brain studies of domesticated animals, for example, have shown as much as a thirty-five percent reduction of growth in their visual cortices relative to non-domesticated species. Presumably—given the unstable diet of non-domesticated animals compared to those in domestication—this size variance arises from the limited visual experiences of domesticated animals relative to the rich and varied experiences of wild animals. Therefore, given their equivalent brain size, the distinction in intelligence between Neanderthals and modern humans was likely not experience.

    I think the key to this intelligence difference is suggested by the Neanderthals relative lack of innovations given their long history. There is a measure of forethought and sophistication in the design of early human artifacts that is missing from the artifacts of the Neanderthals. This forethought and sophistication suggests to me that intelligence between these two species was probably about the faculties or mental abilities their brain function provided. The mental capabilities of early humans—as suggested by their tools, cultural artifacts, and proliferation—likely exceeded those of the Neanderthals. Innovation, forethought, and sophistication suggest to me a more evolved forebrain function with emphasis on prefrontal function. There could have been a functional or structural distinction limiting the sophisticated thought processes of the Neanderthals. All this to say, I think brain size is not as important as function and structure with regards to intelligence.

    (If this is off topic, pardon my lecture.)
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  9. #8  
    Administrator KALSTER's Avatar
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    Innovation, forethought, and sophistication suggest to me a more evolved forebrain function with emphasis on prefrontal function. There could have been a functional or structural distinction limiting the sophisticated thought processes of the Neanderthals.
    I think I read once that judging from the shape of the skull/cranium of Neanderthals, it looks like they did have smaller forebrains in comparison, but likely had better memories, which in turn could have been specifically beneficent for their method of finding food etc. Their brains do still fall within the same index region though, if I am not mistaken. I would agree that looking at brain structure would be one of the pertinent methods of gauging differences in mental capabilities between species that fall within the same index range. I am no expert though. :?
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  10. #9 Re: The Brain between Species and between Humans? 
    WYSIWYG Moderator marnixR's Avatar
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    Quote Originally Posted by Golkarian
    Brain size to body size ratio seems to have an effect between species but not between two individual humans. Any thoughts as to why this is?
    i wonder whether your observation is merely a statistical artefact, since you're not comparing like with like

    in the case of between-species variation you're likely to compare the average brain size of the species involved, whereas within the human species you're comparing individual data points with the population average

    i suspect that these 2 types of comparison are not statistically equivalent
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  11. #10 Re: The Brain between Species and between Humans? 
    Forum Masters Degree Golkarian's Avatar
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    Quote Originally Posted by marnixR
    Quote Originally Posted by Golkarian
    Brain size to body size ratio seems to have an effect between species but not between two individual humans. Any thoughts as to why this is?
    i wonder whether your observation is merely a statistical artefact, since you're not comparing like with like

    in the case of between-species variation you're likely to compare the average brain size of the species involved, whereas within the human species you're comparing individual data points with the population average

    i suspect that these 2 types of comparison are not statistically equivalent
    Interesting, it would however be possible to alleviate this by collecting groups of humans with the same brain to body ratio, and comparing them. I wonder if the results would be different? Does anyone know of any studies like this?
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