Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How is instinct possible?

  1. Dec 18, 2008 #1
    Instinct, by definition, is a hard-wired behavior. It does not have to be learned.

    Therefore, it is passed on from generation to generation.

    Therefore, it is encoded in DNA (as preconfigured neural structures?)

    Therefore, it is a chicken and egg problem.

    Does it mean that a successful (possibly essential) behavior is transcribed to DNA somehow?

    How can DNA aquire a map to the physical world? When you consider that an Arctic Tern circumnavigates the planet during migration, or that a salmon knows how to get back to its place of birth, I am floored as to how this behavior could have been encoded for by chance, and equally floored by the prospect of a DNA transcription process where behavior is essentially 'recorded' in DNA.

    Am I way off base here? Is there something simple that I am missing?
  2. jcsd
  3. Dec 18, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    Yes slightly
    The genetic code doesn't have to encode the learnt facts - the DNA just has to encode the process of learning.
    A baby has a built in genetic ability to learn language, because the animals that didn't learn it didn't communicate with their species and so didn't mate and pass on their genes.
    Their DNA doesn't have to encode English - a baby would be just as good at learning Klingon.
    Similairly a bird's DNA doesn't code the route to take on a migration - it codes the behaviour to follow all the other birds when they take off.
  4. Dec 18, 2008 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Hi K,
    Do you mean for example, how can:
    - a spider 'know' how to spin a web (without having to learn it)
    - a new-born dolphin 'know' how to swim and come to the surface to breath air instead of inhaling water (without having to learn it).
    - etc...

    Yes, these are "hard wired" and passed down through DNA. The standard paradigm goes something like this. The DNA encodes the information needed to create a brain. It is the brain (neuron structure) which is responsible for causing certain types of behavior. DNA is considered the 'code' responsible for creating the 'hardware' of the brain, and that code has in it, the information needed to create the proper neuron structure. So the neuron structure has encoded in it the 'behavior' which therefore doesn't have to be learned.

    If you're asking, how can that structure get started, because the DNA has to have the proper code in order to create the brain with a specific hard wired structure (thus the chicken/egg problem) I think you only need to turn to evolution to understand how DNA can be modified through generations. Perhaps you can better phrase the question.
  5. Dec 18, 2008 #4
    i'd be very surprised if salmon are encoded to a specific stream. more than likely they form an imprint based on the smell of their environment when young. even in humans, smells evoke some of the deepest memories and emotions. which makes sense, since finding food and avoiding poisons is a matter of survival.
  6. Dec 18, 2008 #5
    I get no satisfaction from this answer. That is worded clumsy, but I hope you know what I mean.

    I can accept the learning explaination, but instinct by definition is not learned. Many are not even consciously engaged.

    I can even buy the bird-folllowing-bird scenario to some degree, but even that does not explain why certain aspects of migration such as how birds 100 miles apart will begin their migration at the same time and head to the same place.

    Somehow they all know where to go, and there has to be cases where a bird or a flock have begun a first migration alone without an experienced navigator.
  7. Dec 18, 2008 #6
    Logic says that instincts must be selected for over time, but some instincts are so complex that it's hard to stomach as a purely random manifestation.

    I also have never heard of a frog that tried to fly south for the winter, and you would thing that as a random process... I don't know.

    The fact that we don't know is interesting in itself.
  8. Dec 18, 2008 #7
    Even if a salmon does employ some kind of marker or sense, it still requires a very sophisticated set of behaviors.

    Wiki says that salmon spend as much as 5 years in the open ocean, but it does not say how far they range there, only that they may travel hundreds of miles to get back to their spawning ground.

    I'm surprised the salmon has not pressured itself out of existence. Them and penguins. The hell they go through just to satisfy the instinct to breed.

    Now that is a powerful instinct.
  9. Dec 20, 2008 #8
    Instinct is just governed by evolution.
    It can be done in steps to show how just because it seems complex does not mean it cant come from a simple process.

    1st example would be breathing. A process humans do without thinking. Anyone who cant breath dies. If a baby does not get the information on how to breath to a baby before its born it dies. Hence the baby's knowledge on how to breath is passed on from the mother before birth which must be in genes.

    Step it up a level. Spiders just knowing how to make a web is the same. If they could not make a web they would die and hence not reproduce and hence not pass on the DNA holding the information to build a web.

    and so on up the difficulty curve.

    Migration paths will be learned by following older individuals in the migration. If they do not follow they will die and again wont pass on the genes that say "follow your parents/crowd"

    I think the problem lies in that you are thinking these things come about randomly. They come about through evolution which is not random at all. Creatures will slowly evolve to particular behaviors and despite looking complex there will always be a set of small steps to something very basic. Over the very long periods of time complex actions can come about from evolution from something rather basic in comparison.
  10. Jan 14, 2009 #9
    It's not that, I understand things are pressured in certain directions.

    I'm saying that things like migration paths are more than just learned by following, they are in the genes. If these complex behaviors are selected for, then so be it; but I wonder if there might not be additional help somewhere.

    After all, the time it takes to get to some current state of instinctual behavior, if driven purely by selection, would indicated that many other attributes may have had the chance to manifest during that time. Things like changing skin color I would think would be beneficial to any species, and the fact that it occurs at all would imply that most species would eventually have this ability.

    I don't know; my gut tells me it is natural selection plus something else, such as reverse transcription of some sort.
  11. Jan 14, 2009 #10


    User Avatar
    Gold Member

    As an example, let's look at elvers. These are tiny, almost transparent baby eels that come to Maine's rivers to grow in fresh water. When they are mature enough, they head out to the Sargasso Sea to breed, and their spawn comes back to Maine. The elvers have never been in a Maine river, nor do they know the smell of fresh water, having hatched in the ocean, and having spent most of their brief lives swimming the Atlantic to get here. How do they know to "come home" to waters where they can live relatively safe from predation, so that they can mature and head back to the Sargasso? It's not learned behavior. If you could see a bucket of those little glassine creatures, you'd have to wonder how such behavior could be hard-wired into such tiny little nervous systems.

    As an aside: Elvers have a fair degree of protection here, in part because years ago, the Japanese were paying over $2000/lb for them live-shipped to Japan to stock eel farms. Over-fishing resulted, and strict regulations with tough penalties had to be instituted to protect enough of the returning elvers to ensure viability of the population.
  12. Jan 14, 2009 #11
    Steven Pinker disagrees with you. read 'the language intstinct'.

    theres nothing really extraordinary about instinct. we have lots of instincts. we are born with mental modules that process visual/auditory/tactile information. we take it so much for granted that we dont even notice it but it would in fact be extremely difficult to get a computer to do what a newborn instect does easily.

    babies learn language but dogs never do. yet both have the 'process of learning' encoded in their dna.
  13. Jan 15, 2009 #12


    User Avatar
    Gold Member

    I think you'll find the cause of mutations to be the random factor in the development of an animal's instincts. The mutations are caused by the organisms interaction with the environment.

    I think it's hard for you to imagine such complex instinctual "manifestations" or developments because these developments have taken place over 100s of millions of years. In some cases billions of years. It depends on the species we're talking about.

    Salmon have been around along time. Or, at least their predecessors have. We're talking about probably over 250 million years. Every generation during every one of those 250 million years is subject to environmental adversities and challenges.

    Each generation there is a modification in the gene pool of the species because a certain feature was advantageous for a certain number and helped that portion of that generation survive. And the modification or "mutation" remains while the individuals without it do not.

    Let's say a Salmon's generation cycle is about 7 years. Multiply these changes by 7 into 250,000,000, = 35,714,286 generations of evolutionary development... and development of instinct.

    36 million generations represents enough time to develop some pretty complex instincts.
    Last edited: Jan 16, 2009
  14. Jan 16, 2009 #13
    This is a standard misconception that probably stems out of creationist's fallacious arguments against evolution. A complex instinct didn't just randomly spring into existence in a couple of individuals after which those individuals were selected, but the instinct itself gradually evolved from simpler behaviours, each of the steps being favorable for the individual in question.
  15. Jan 16, 2009 #14
    What instincts do all humans share?
  16. Jan 16, 2009 #15


    User Avatar
    Gold Member

    One common instinct is to "google".
  17. Jan 16, 2009 #16
    I just googled that and it said on wiki that it's a common misconception that googling is an instinct?

    Now I'm just confused?

    Is it true that if you type Google into Google it can break the internet?
  18. Jan 16, 2009 #17
    the language instinct
  19. Jan 16, 2009 #18
    The instinct to learn language you mean. Ok got that one from before what else?
  20. Jan 16, 2009 #19
    All of them, by definition.
  21. Jan 16, 2009 #20
    ? :confused:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook