Encephalization of early hominids

Discussion in 'General Science & Technology' started by Billy T, Mar 5, 2015.

  1. billvon Valued Senior Member

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    You have given a reason that humans SHED hair. But you claimed that humans NEEDED hair to avoid overheating. (Quote - ". . . need that hair to avoid over heating".)
    Now you are giving reasons that people need that hair in hot desert climates.

    So you are saying two things here. One is that people need hair in desert environments to block sun - the other is that people cannot have hair in hot environments so they can dissipate heat. They seem contradictory. And your example of how bedouins need to wear clothing seems to argue against your claim that bare skin is preferable in desert/savannah climates.

    Now let's move on to the food issue:

    So honey, termites, bananas and papayas (for example) do not provide much energy?
     
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  3. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    No. You are very close to putting words in my mouth or actually doing so at several points. The closest thing I said in post 60 to what you claim I am saying is:

    "Most humans don't need to block sunlight from reaching their body FOR THERMAL REASONS*; however, humans who live in or transit hot solar deserts keep most of their body covered with more than one layer of cloth. For one who does not understand what I have been explaining about the importance of NOT letting the solar heat get to the body, this use of thick layers of cloth by the Bedouin and other desert Arabs seems strange.
    * Skin cancer is a different reason."

    I did not say, as you claim I did:
    "But you claimed that humans NEEDED hair to avoid overheating. (Quote - ". . . need that hair to avoid over heating".)
    As that is obviously false as humans have very little hair compared to the apes, I would not have said that; but I have said that humans retained the hair of their heads, in large part for thermal reason. Where is your "Quote" from? I re-read post 60 twice trying to find it. I could not even find the words "to avoid over heating."

    I may have said that somewhere else about Apes, but not about humans, except to note that most human heads are covered with hair as the brain is very energy intensive and could get into thermal trouble under a hot sun without hair or a replacement for it, called a "hat."
    No, again did not say that. Humans are able to adapt to both intense sun and intense cold, via clothing, and do so. The same erroneous logic that lets you read my noting that Bedouins, etc. use layers of cloth in the hot desert, would let you convert an observation of mine that in Alaskan winters people use insulating jackets and thick gloves, into a claim that I said: "People need fur in cold climates.", which is an exact parallel to part of your claim now bold above.
    NO. I said neither of those. You, with the false logic just discussed, twisted what I said or misunderstood it. Bedouins don't need hair over their bodies to block the sun.
    On the second (... Can't have hair in hot environment...) I never said that either! I did note that the fact humans have hair on only a tiny fraction of their bodies and not a cm thick layer of hair as Apes do, does increase the cooling that evaporation of human perspiration gives. With thick hair that cooling would be greatly reduced especially when there is little or no wind.
    No. It doesn't as I never claimed "bare skin is preferable in desert/savannah climates." that is just more words you are placing in my mouth. I said exactly the opposite: That bare skin is a hazard to health in hot deserts - why Bedouins use layer of cloth over almost all of the bodies. I. e. It is NOT preferable to have bare skin under the hot sun - and noted also that was true to reduce chance of skin cancer also as well as for thermal reason of blocking sun light, especially the IR, from striking the body.
     
    Last edited by a moderator: Mar 12, 2015
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  5. Fraggle Rocker Staff Member

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    It's been estimated that members of our ancestral species, who had developed the technology of flint-knapping and therefore were carnivores, but had not yet developed the technology of controlled fire and therefore had to eat their meat raw, probably spent four hours of every day simply chewing their food.

    Nonetheless, I have never seen a report from an experiment in which a modern human went on a raw meat diet to test this hypothesis.

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    My father worked in the Chicago stockyards during the Great Depression. They had a rule: You can eat all you want on the job, but if you try to take any meat home you'll be fired. So all the workers developed a taste for raw beef. However, they had meat grinders so it was ground beef they were eating, not big slabs. Raw ground beef is easy to eat, if you like it. My dad turned me on to it when I was little, so I developed a taste for it. But the last time I had any was more than fifty years ago.
     
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  7. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    That is my understanding too. Meat is a high energy food - in some ways it is "pre-concentrated" vegetable matter, by a factor of 5 to 10. Thus, a diet with a large fraction of meat would reduce the time required for chewing, and if gotten by scraping off small pieces of flesh that the animal which killed another had to chase down, was a relatively low investment of energy also.

    Thus developing the knack for "flint knapping" was quite a big step towards cooking and surely lead to significant specialization - some members of the clan /tribe got good at it and did not need to hunt, gather roots, etc. but could earn their food with their tool making skills. -The start of social organization, even before later there were "cooks" who specialized in cooking food.

    I and the links I have given need to be read in their context - a comparison of how the nutrition of human ancestors differed form other primates and what that difference, especially after cooking made it extreme, let happen - bigger brain and smaller gut. No one is saying honey is not great aid to increasing energy intake per mouth full or that all eating of uncooked berries etc. stopped just because cooking had been discovered. We still eat raw food today and it does not increase the hours needed for getting your nourishment as modern society is highly specialized - our food, by and large raw or to be cooked, comes from the grocery store.
     
  8. Trippy ALEA IACTA EST Staff Member

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    Billy T:

    I hope you're planning on responding to this in some way some time soon?

     
  9. billvon Valued Senior Member

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    Agreed. In contrast with the various "complete" theories floating around (like the recent Aquatic Ape theory, where one simple theory explains everything) I think it was a gradual process. Hunting with simple tools allowed access to higher calorie foods; better butchering allowed access to easier to chew, higher energy foods (fat, liver, etc.) This allowed - gradually* - a larger brain with the same gut to develop. As the brain developed, the development of stone tools and weapons accelerated, which allowed further brain development. At some point the development of our brains could at least support the intelligence needed for the use of fire, and eventually we adopted it for our use.

    (* - gradually in this case meaning around a million years)
     
  10. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I already have:
    But I can expand the details giving yet a third reason why the cooling problem of bigger brains is WORSE than for smaller brains - Actually the main reasons why the brain is so energy demanding, even when with low rate of neural activity in some parts of the brain:

    99.9+ percent of the brain is far from the thermodynamic equilibrium state and keeping it in that state requires a great deal of energy, mainly for the "sodium pump." That pump*, like all pumps, needs energy to prevent equilibrium from naturally occurring. In this case it is fact that brain cell neurons, especially their axon are with internal electrical potential of - 70mv wrt the external electrolyte. That voltage is called the "resting potential" - a poor choice of names, as it is the hard-working, energy consuming, normal state of brain cells. Only when an "action potential" is traveling down the axon is that part of the axon in quasi-equilibrium. (Same concentration of Na+ ions briefly on both sides of the neural membrane.) It is the "sodium pump" that pumps the positive Na+ ion out of the interior to maintain this almost always existing dis-equilibrium state against ionic diffusion.

    The energy dissipation rate (the heat generation) of the sodium pump is AT LEAST directly proportional to the brain volume, but would be disproportionally larger in larger brain as some axons would be longer than the average length in a more compact brain.

    This, the Na+ pump's energy use, is a large cause of heat production in the brain, I did not mention it at the end of post 60 as it is more complex to explain, but it is probably a more important reason that the two factors I did mention (worse surface to volume ratio for cooling & greater blood flow energy dissipation in the larger volume of capillaries). I only noted that all the cooling problem of a larger brain is WORSE than for a smaller brain and asked, as the last sentence:
    "Please, some one, explain why bigger brains relive / reduce thermal stress"

    Now, as you asked me specifically to comment, I ask you to explain how bigger brains relive / reduce thermal stress. I .e. please refute my observation that the "thermal stress" argument as the cause of bigger brains has everything just backwards.
    - - - - - - -
    * How that Na+ pump worked was not well understood 35+ years ago. I have forgotten much that I once knew about brains, when I assisted at many brain operations on Rhesus monkeys, and had to finish one that was in progress when the JHU neuron surgeon doing it was called back to the hospital to be there when a head injury accident victim would arrive. I have held both rhesus and human brains in my hands and compared them. I am certainly not an expert now, but once knew a great deal about brains.
     
    Last edited by a moderator: Mar 13, 2015
  11. Anew Life isn't a question. Banned

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    don't bother saying "no it is "not true I'm a stuckist bigot. "don't bother.

    some believe that a hominid: is "something at it's complete showe like an rose or roses at their blossom aeon''
     
  12. Trippy ALEA IACTA EST Staff Member

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    This is a straw-man hypothesis:
    Nobody has claimed that bigger brains relieve/reduce thermal stress in the sense that you mean here. You're still focused on the cooling aspects of the discussion, but the claims being made don't revolve around cooling (but enhanced cooling can explain other evolutionary changes that are observed alongside increased encephalization).

    The claim that's being made is that the large and interconnected nature of the brain means that the damage caused by killing off a bunch of brain cells through repeated exposure to heat stress is less damaging than it would be for a smaller, less interconnected brain.
     

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