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The cause of evolution of human brain?

  1. Oct 30, 2012 #1

    I was interested in human consciousness, and I picked up Daniel Dennett's book "Consciousness Explained" and something he claims there got me thinking:
    He says that human brain evolved from chimp-size to homo-sapiens-size in a period after humans learned to stand on 2 feet, and before the appearance of language. What was the evolutionary "pressure" then, that caused this evolution, if we didn't need it to be erect and we didn't use it for language at the beginning?
    The book itself isn't exactly new, is it possible that there have been some research that shows different order of events? If so, could you point me to such research?
  2. jcsd
  3. Oct 30, 2012 #2


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    I don't think there is a clear answer to the question of human brain evolution, I remember reading about at least two or three theories. Unfortunately the only one that I remember reasonably well and I can point to the source is the one saying that human brains evolved to increase our chances to outwit other members of our species while competing for sexual partners (see The Red Queen: Sex and the Evolution of Human Nature, by Matt Ridley).
  4. Oct 30, 2012 #3
    Speaking broadly, clearly language is not the only benefit of a larger brain, especially for animals that are relatively slow and weak. Language is not requirement for greater cleverness to be an evolutionary advantage.

    I'm no biologist, but if I remember correctly from my physical anthropology course (2 years ago), that is, in fact, the correct order of events.

    Secondly, the "beginning of language" is hard to pin a meaning down to, so it matters was his definition of language is. It's also difficult in the sense that there is obviously not an obvious physical record of it, and apparently some scientists argue for evidence from physical structures like the larynx, while others argue that such features are irrelevant. Anyway, I assume that Dennett is referring to a symbolic language, rather than a simple proto-language. Read: http://en.wikipedia.org/wiki/Origin_of_language#Evolutionary_timeline - particularly "Early Homo" and "Archaic Homo sapiens"
  5. Oct 30, 2012 #4


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    One difference between us and our common hominid ancestors, for example, is that humans have three like copies of SRGAP2, while other hominids have only one. Such genes are associated with the stimulation of new dendritic spines (which means increased connectivity).

    Nature 486, 481–482 (28 June 2012) doi:10.1038/nature11380

    MYH16 is another gene thought to be associated with brain evolution. Most animals have a good copy of this gene. Humans, however, suffered a defecting mutation that caused us to lose muscle mass in our jaws. This certainly could cause problems for survivability in a harsh pre-civilization, but we somehow survived that issue long enough to take advantage of the newly-available space it left for brain development.

    Nature, 428, 415 - 418,

    You will find many, many more, brain gene differences in the introduction of this paper:

    Nature 443, 167-172 (14 September 2006) | doi:10.1038/nature05113
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  6. Nov 1, 2012 #5
    Thanks for all the answers!

    Interesting, so what you're saying is that it's possible that our brain size is just a byproduct of some other mutations, and wasn't originally a feature selected for? Somehow I thought that the gradual rise in size of a brain demands some justification in cost-benefit terms.
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  7. Nov 1, 2012 #6


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    It probably did at some point (through selection pressures). But the initial mutation (or set of mutations) is/are always random, as far as I know. It's just a matter of coincidence that the mutations happened to be beneficial later. So I think what you say is true to some extent, each incremental mutation that increased our chance of thinking our way out of death and into reproduction were favored. If the necessary mutation was "bigger brains" then so be it (organizational structure is important too though!)

    But... a mutations doesn't really "cost" anything itself. The resulting effects when applied to environment might both cost and benefit in different domains, but it's not like some internal system figures out, ahead of time, the cost/benefit ratio like a sustainability engineer would.
  8. Nov 1, 2012 #7
    Ready, aim, FIRE !-)

    None of the references that I found say that walking erect came after intelligence. Paleontology research over the few decades say that walking erect came before intelligence of any sort.

    Many vertebrates walk erect without having human type intelligence. Birds walk erect. Some extant lizards walk erect. Many dinosaurs (theropods and hadrosaurs) walked erect. Obviously, these animals couldn't walk erect if it required language or intelligence.

    I think that learning to throw a projectile accurately was the biggest step toward human-like intelligence. This is what brought us out from monkey-hood to killer ape.

    Humans are just “lucky” that a series of unlikely adaptations occurred in series that together form integrated intelligence. I think the two most critical steps, lifting us slightly ahead of cetaceans and elephants, is throwing learning to throw projectiles and learning to make tools. However, I think that throwing projectiles was probably the “biggest” step toward making a human-type intelligence.

    Two important functions for the brain that preceded complete language are tool using, tool making and throwing projectiles. Some currently held theories claim that the evolution of the brain for throwing projectiles was a preadaptation for tool making.

    Tool using and tool making are aided somewhat by the erect posture. However, a fully erect posture is not necessary for tool using. Even elephants, which have no hands and walk on all four limbs, can use objects that they find as tools. However, tool making requires a little facility at using a free hand. The precursor to making a tool may have been throwing projectiles.

    Throwing projectiles involves brain calculations of direction, wind speed, gravity, etc. Even if most of the calculations are unconscious, the calculations have to be made.

    Climbing trees was probably a precursor to throwing objects as projectiles. Grabbing a branch, holding it and letting go would be good first steps for throwing a projectile.

    Animals often learn by imitate their parents and neighbors. However, once a few primates learned to make tools, language was probably useful in passing the information to their children.

    So I am suggesting a possible geneology to intelligence that looked like this:
    1) Climbing trees: resulting in knowing how to grab things.
    2) Using tools: Learning to move those things in a certain way.
    3) Throwing projectiles: learning to extrapolate the motion of things after letting them go.
    4) Making tools: Learning to throw one rock or piece of wood against the other.
    5) Language: Explaining to relatives how to make a tool.

    Here is an article on primate intelligence that mentions both tool use and rock throwing.
    “Tool manufacture and use are virtually non-existent among non-human primates. However, gorillas, common chimpanzees, bonobos, orangutans, and capuchin monkeys are notable exceptions. Some of them use very simple tools to help in acquiring food and water. For instance, chimpanzees have been observed stripping the leaves from twigs to make probes to get termites and ants to eat. They use similar modified sticks to obtain honey from beehives in tree trunks and from up to a meter underground in subterranean hives. Twigs are also used by them at times as toothpicks. Crinkled leaves are employed as sponges to get water from hollows in trees for drinking. Rocks and broken tree branches are used to crack nuts and sometimes to throw at other chimpanzees in order to intimidate them. Rocks are used at times as projectiles in hunting bush pigs and other small game.”

    Here is an article on human evolution that mentions throwing projectiles.
    “Hominids have considerably elaborated the capacity to aim and throw, which is a homology passed down from the common ancestor of humans and apes. Without it we never would have developed projectile technology and weaponry—or baseball.”

    “Now however, researchers studying such behavior have come to the conclusion that throwing feces, or any object really, is actually a sign of high ordered behavior. Bill Hopkins of Emory University and his colleagues have been studying the whole process behind throwing and the impact it has on brain development, and have published their results in Philosophical Transactions of the Royal Society B.”

    Read more at: http://phys.org/news/2011-11-poop-throwing-chimps-intelligence.html#jCp

    This article shows that standing on two legs is not a requirement for learning to use tools.
    “Elephants exhibit a wide variety of behaviors, including those associated with grief, learning, allomothering, mimicry, art, play, altruism, use of tools, compassion, cooperation,[3][4] self-awareness, memory and possibly language.[5] All indicate that elephants are highly intelligent; it is thought they are equal with cetaceans[6][7][8][9] and primates.”

    “Elephants show a remarkable ability to use tools, using their trunks like arms. Elephants have been observed digging holes to drink water and then ripping bark from a tree, chewing it into the shape of a ball, filling in the hole and covering over it with sand to avoid evaporation, then later going back to the spot for a drink. They also often use branches to swat flies or scratch themselves.[30] Elephants have also been known to drop very large rocks onto an electric fence either to ruin the fence or to cut off the electricity.”

    This link states the just lucky theory of intelligence. It points out that there is a nested series of requirements for a species to become intelligent in the way human beings are intelligent.
    http://websrv-gr.server.gvsu.edu/cms3/assets/6D2549F6-ED41-142A-2D7251DEDEE796B4/deanerfiles/2vanSchaiketal1999PrimateMaterialCulture.pdf [Broken]
    “The nested set of conditions hypothesized to favor feeding-tool use, from ecological opportunities and manipulative abilities as preconditions to cognitive factors and social conditions favoring the invention and transmission of tool-using skills in captive or wild populations. On the left side, a summary is given of the taxa meeting the ever-narrowing requirements, on the right side the phenomena shown by the taxa mentioned on the left.”

    In the diagram with the last article, it lists throwing projectiles. Lots of things were needed for intelligence, but throwing projectiles was an important step.

    So play ball!
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  9. Nov 2, 2012 #8


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    Cantstandit, just a thought I had: the neural system and the proper throat and vocal chord muscles would have to have both evolved (in some way probably independently, similar larynx to humans can be found in other animals). The neural system wouldn't just be a way to control the muscles, it would also have to have some way of encoding a series of muscle commands into a concept (something our temporal lobes participate in).

    An interesting thing about the development of humans is our heads get so big as fetuses that we leave the womb much earlier than other animals, so a large part of our development we're already being exposed to lots of information and that developmental process provides an avenue for a lot of social influence.

    Feral children (who aren't raised around language, or really other people at all, or are neglected or treated poorly by them) have no language and have never been shown to learn language (there's a critical period during which language must be learned). Some have learned sign language, but apes can also do that.

    So there's something important about social interaction during development.

    Thought Experiment: Totally against all ethics, but what would happen if you raised like four or five new borns, fed them, cared for them, loved them, maternal mothers breastfed them, but no one ever talked to them, and let them most of the time care for themselves among only themselves (under supervision to ensure safety and provide verbless mental and physical challenges to enrich their learning experience, of course. No neglect.)

    And you continued like this through the critical period for language.

    Would they come up with a rudimentary language to communicate between themselves? Even if it's grunts and clicks or something? I think they would.
  10. Nov 2, 2012 #9


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