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How much are we genetically pre-programmed

  1. Oct 11, 2012 #1
    I am a complete layman in this but have been wondering about what makes us us.
    While I think I am right in saying the brain works on electrical and chemical impulses there also appears to be what I would call rom and ram (from computing) or instinct and learnt behaviour, how much is genetic pre-programming. I ask this from observations about birds which seem at least to me about halfway between higher and lower animals.
    The thing with birds is that you can tell the species, generally, just from looking at the nest. Nestbuilding as far as I can see is not taught yet is extremely complicated in some species. Birds of the same species will build the same nests using the same materials, you cannot tell the difference between a novice and one that has built previously, a ground nesting bird will build on the ground etc. This to me suggests that how to build, what materials to use and where to build are all genetically pre-programmed, whereas finding food is taught, I have seen this.
    The higher up the scale you go the less seems to be pre-programmed and the more taught. I wonder though how much of our makeup is genetic and how much learnt. Children brought up much the same can be completely different to the extent that upbringing cannot explain, there are characteristics that seem to be inherited.
     
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  3. Oct 11, 2012 #2

    Simon Bridge

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    This is the "nature vs nurture" debate - the best answer is "nobody knows".
     
  4. Oct 11, 2012 #3

    Ygggdrasil

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    In many animals, basic instincts and behaviors are encoded in the organism's DNA. The DNA provides instructions for the body to build specific genetic circuits to perform certain behaviors in response to certain stimuli. For example, flies have an escape response triggered by certain stimuli, such as a shadow passing over them. Researchers have identified a specific nerve cell in the fly that controls this response and this nerve cell is the same in all flies of the same species. Artificial stimulation of this nerve cell triggers the escape response.

    In humans and other higher mammals, the situation is very different. Whereas most animals are born with innate behaviors and instincts, humans are born with very few innate behaviors and instincts. For example, many animals (insects, fish, reptiles, amphibians, etc.) are fully capable of walking, feeding themselves and even surviving independently after birth. In contrast, human babies can do practically nothing after birth. The difference is that the DNA of humans does not specify a wiring diagram for the brain. Rather this wiring diagram is formed on the fly on the basis of the experiences of the individual. For example, if you were to take a newly born baby and cover its eyes for its entire early childhood, the child's neural circuitry for interpreting visual stimuli would not develop and the child would be blind despite the fact that the child's eyes work perfectly well. Another consequence of this strategy is that everyone will develop different neural circuits to perform the same functions. For example, whereas the same nerve cell will trigger the same escape response in all flies, activating a specific nerve in humans would likely trigger very different responses in different individuals.

    While this wiring-on-the-fly strategy has many disadvantages in the younger phases of life (babies and children are very much dependent on others for survival), this plasticity of the brain associated with the wiring strategy gives humans an unparalleled ability to learn. This is one reason why humans have learned how to do things like create a system of reading and writing while other organisms have not.
     
  5. Oct 11, 2012 #4

    Pythagorean

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    Human babies are of course still born with several consistent muscular reflexes: the Moro reflex, the Palmar and Plantar grasps, sucking and rooting reflexes (for eating), and many more.

    They also have a smile reflex when they pass gas and have several different cries with their own meaning.

    From there, lots of behavior is learned through social feedback from the parents. Once they can crawl and explore, they star becoming little hypothesis generators (and testers!) and it's essentially up to the parent to safely guide their hypothesis testing and expose them to new observations and experiences.
     
  6. Oct 15, 2012 #5
    I would like to express some further thoughts regarding instinct.
    From post 3 these are encoded in the DNA. Going back to birds, a bird that builds a nest out of mud say must do so out of instinct, they have no-one to teach them what mud is to begin with so mud must be built into its preprogramming and so with different birds using different materials also the size and shape of the nest and where it is built.
    Instinct also seems to use a lot less brain capacity, the smaller the brain the greater the level of instinctive behaviour.
    While we take it for granted that we learn about and how to use our environment is it possible that environment and its use can substancially be encoded in DNA, am I right in thinking that in lower animals such as insects thier existance is almost completely instinctive which would mean that almost everything they need to know about how to live and survive is in thier DNA not just how the body is put together and how it works.
     
  7. Oct 15, 2012 #6

    Simon Bridge

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    No.

    How their bodies are put together is a big part of their behavior.
    eg. A fly can land upside-down on the ceiling.
    It's actually a complicated process... the instructions to do it are not in the DNA - the DNA is too small: especially if you want to include all the other possible surfaces, other things the fly has to be able to do, and the "junk" parts. But the DNA includes a recipe for building a fly ... and part of the physiology is a switch that says when the leg-hairs are pressed, the wings stop beating - and the leg hairs stick to surfaces. To land on the ceiling, all the fly has to do is reach out with a leg and touch it - the wings stop beating, the leg sticks, the fly swings around and the other legs cushion what is otherwise a crash. (To take off again, the fly has to jump - unsticking all the feet, the wings start beating. This is all hardware.)

    This is a much simpler that coding for a landing process, and comes from the behavior, environment, and physiology, feeding into each other. This feedback effect can be very subtle and is what leads to the complexities of living things.

    Not all the instructions to build a fly are in the DNA itself - a fly is built by interaction of all the bits of a fly egg. That's why I described it as a recipe rather than a blueprint. A recipe does not contain every single instruction either... eg. the recipe says to bring water to boil ... it does not tell you what altitude to do this at (the boiling temperature varies with altitude) - the recipe will only work under some conditions. Similarly DNA to build a fly won't work if it is placed in a chicken egg. You don't even get a weird hybrid fly-chicken.

    You also need to be careful thinking in terms of "higher" and "lower" creatures. Every creature alive today is at the same evolutionary "level". There are all kinds of hierarchies possible and they tend to be worked out to put humans on top... scientists can be pretty arrogant but there are humilities in science: one of the humilities comes with the realization that humans are just not important - and being OK with that.

    (It took me quite a long time to appreciate how subtle all this is.)
     
    Last edited: Oct 15, 2012
  8. Oct 16, 2012 #7
    Hi Simon.
    When you say no are you saying that I an completely wrong. Does the fly actually know then that it is flying.
    A fly is surely born to fly, this is more fundamental than what you have described.
    Going back to birds and nests, how does a particular species of bird know what to build its nest out of, surely it must be born knowing the difference between mud and straw for example, otherwise nests would be built out of whatever was available.
    I meant higher and lower intelligence our importance I think depends a lot on your religeous leanings.
    A recipe of course requires you to know what the ingredients are. A cake recipe is useless if you dont know what eggs, flour and sugar are. How does DNA know its using the right ingredients, i.e iron for blood, calcium for bones etc without the ingredients being labeled somehow.
     
  9. Oct 16, 2012 #8

    Pythagorean

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    Animals (including humans) don't have to know, they just have to behave appropriately. Of course as humans, we know that we know some things and can share and talk about it with each other. We can't ask a bird, though they share some brain homology with us. It's not likely that a fly "knows" in the same way a human does. Completely different architecture, not nearly the neural systems we have.

    DNA doesn't "know" at all. DNA is a molecular configuration that survived, many configurations failed to persist. It's like throwing a die and keeping the 2's. The die doesn't know it needs to be a 2 to survive, it just survives because it wasn't destroyed by the selection criteria.
     
  10. Oct 16, 2012 #9

    Simon Bridge

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    Is a fly conscious? Anybodies guess.

    When I said no I also told you what I was disagreeing with.
    I said the relationship between behavior and DNA is more subtle and complex than your statements so far would suggest and provided an example. DNA does not work the way you seem to think it does.
     
  11. Oct 18, 2012 #10
    If DNA doesnt know then what does. Everything needs instructions in order to function.
    Why do bird species use different nesting materials rather than whatever is available.
    We build out of local materials and design our houses this is obviously learnt behaviour and completely different, we are not born with the knowledge unlike the birds.

    Animals (including humans) don't have to know, they just have to behave appropriately.
    How do they know what is appropriate behaviour.
    Physically at least we are no more than biological machines, a machine cannot run without instructions.
    I am willing to accept that DNA has nothing to do with those instructions but I fail to see where else they can come from.
     
  12. Oct 18, 2012 #11

    Pythagorean

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    They don't have to know, it just has to feel good. DNA instructions are like "go left, go right" and they just happen to get you to Vegas. The instruction is nothing like "go to Vegas". That's just where the instructions happened to lead you.
     
  13. Oct 18, 2012 #12

    Simon Bridge

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    ... and if you started out in the wrong place, the instructions will take you someplace else.

    DNA just codes for other molecules ... these molecules just feel electromagnetic forces. The behavior of the organism is emergent behavior. At best you just feel attracted to certain motions... "move so the nice smell and the pretty lights are closer": you won't find anything in the DNA that says that.

    One of the ways to get a feel for this sort of subtlety is to study cellular automata.
    If you play http://en.wikipedia.org/wiki/Conway's_Game_of_Life]the[/PLAIN] [Broken] game of life - for example - you see groups of cells behaving in regular ways ... yet there is nothing in the underlying rules which tell them to do that... not in so many words.

    It is not surprising that people have a hard time with the idea that all this need not have a controller at least programming in the rules at the start.
     
    Last edited by a moderator: May 6, 2017
  14. Oct 18, 2012 #13

    Drakkith

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    DNA is a blueprint for how to physically build an organism, which reacts the way it does thanks to the way it is put together? Is that pretty much what you are saying?
     
  15. Oct 18, 2012 #14

    Ryan_m_b

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    Blueprint is an often used but incorrect analogy. DNA sequences are nothing more than a template for RNA whose transcription is dependent on mechanical environmental factors. It's a really hard concept to get across but there are no genes for specific behaviours, those emerge out of a complex interplay between all the biochemical elements and that of the environment.

    Let's use the example of the hypoxia response as it's quite simple. Hypoxia is a state where oxygen demand exceeds supply. The hypoxic response is a series of behaviours that cells enact when in a state of hypoxia such as increasing anaerobic respiration, releasing angiogenic factors to encourage blood vessel growth towards them, stimulating red blood cell production etc. But there is no gene for any of that, there's no set of instructions that say "if the oxygen levels drop by X then perform the following". Instead when a cell enters a state of hypoxia an oxygen dependant reaction that leads to the degradation of hypoxia-inducible-factor 1A halts. Because of this HIF-1A (a protein constantly synthesised before being degraded in normoxic conditions) accumulates, migrates into the nucleus, becomes HIF-1 and binds to a series of promoter sites on the DNA sequence that activate a bunch of other genes.

    There's no higher order command, it's all unthinking and reactive.
     
  16. Oct 18, 2012 #15

    Drakkith

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    I'm taking that to mean we act certain ways because we are built certain ways. :biggrin:
     
  17. Oct 18, 2012 #16
    Epigenetics anyone?

    Also, there are more bacterial cells in your body than human cells, and DNA transfer is known to happen. What's the effect of that?

    People hardly know anything about the bacteriome. Also, much is also not known about the function of the majority of DNA, which is labeled as "junk" DNA, that really isn't junk at all.

    Why do identical twins have the same DNA, but act differently?

    Read up on the mosaic model of brain development, which is quite fascinating. Mutations happen all of the time neural stem cell differentiation. Mutations can arise at any step in the series of >100 billion cell divisions required to generate the number of neurons found in the fully developed brain, resulting in variably sized populations of neurons that share a unique somatogenetic inheritance. Chances are high that an individual who inherits a recessive mutation in a critical gene will have some subset of neurons in which the same gene is also mutated. This may represent an entire brain structure (e.g., cerebellum), smaller regional structures, or even scattered populations of neurons that migrate throughout the brain after neurogenesis.


    There may be SOME genetic pre-programming in your DNA, but it's probably not as much as you think.
     
  18. Oct 18, 2012 #17

    Drakkith

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    I've not heard of this before. Do you have a reference by chance?

    To my knowledge the cells in your brain reach out and make connections with other cells during development, but the connections themselves aren't pre-programmed or whatever. The dendrites shoot out in random directions, so the connections are different for every person even if their DNA is exactly the same. Since the connections are different, people don't act the same.
     
  19. Oct 18, 2012 #18
    f
    Sure:

    http://www.wired.com/medtech/health/news/2004/10/65252[/URL]

    We're essentially a bacteria hybrid, and our cells are outnumbered by alien cells.

    Also check out this article that says were really 'super organisms':

    [url]http://www.nature.com/nbt/journal/v22/n10/abs/nbt1015.html[/url]

    Example of gene transfer between alien organisms and eukaryotes:


    [url]http://www.sciencemag.org/content/292/5523/1903.abstract[/url]

    [url]http://www.the-scientist.com/news/display/53552/#ixzz1YEkWvHov[/url]

    Now people are studying the effect of gut bacteria health and its relation to brain diseases like Parkinson's and brain development. Really strange, but quite fascinating.


    [url]http://www.pnas.org/content/early/2011/01/26/1010529108.full.pdf[/url]


    Hardly anyone knows what the overall function of the bacteriome does, what the effect of gene transfer is, or how the bacterial-human symbiotic relationship can modulate development.
     
    Last edited by a moderator: May 6, 2017
  20. Oct 18, 2012 #19

    Drakkith

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    Interesting. I wonder how much of our body weight/biomass comes from these bacteria.
     
  21. Oct 18, 2012 #20

    Pythagorean

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    Last edited by a moderator: May 6, 2017
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