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How did sex evolve?

  1. Jul 5, 2003 #1
    This is a question that, when I tried to look up references, I just got "this is an area of a lot of confusion in the scientific community" type of answers.

    We know that primitive beings do not have sexual relations, but reproduce asexually. How, though, did sexual relations evolve? How and why did beings start to need each other to make more of their species?

    Any comments would be appreciated.
  2. jcsd
  3. Jul 5, 2003 #2
    I don't know if you are aware

    but even at the level of common bacteria there is some exchange of genetic material. And many lower creatures don't show sexual dimorphism, or change their sex at some stage in their life.

    My own theory about sexual dimorphism is that the need to compete triggered it. An advanced organism that had to perform both male and female functions would have problems competing with specialized male and females.
    Last edited: Jul 5, 2003
  4. Jul 5, 2003 #3
    Mentat - I have some WONDERFUL information for you bud.

    Here is a freaking insane piece of biological insight.


    Bacteria are simple creatures. They posess 3 important parts for this discussion. Bacteria have chromosomes which hold their DNA. They also have what is known as a plasmid - This plasmid holds non-chromosomal DNA.

    Bacteria can keep exotic DNA on the plasmid or they can actually put chromosomal DNA onto the plasmid... but why you ask?

    This leads us to the third part.......the PILUS.

    A pilus is a part of bacterial anatomy that they can construct from their DNA.

    It looks like a penis and stick out of their body. What a bacteria is able to do with this pilus is stick it into another bacteria and they can transfer the DNA that is on their plasmid to eachother!!!!!!!

    So if I had some cool new genes that you wanted, I could poke you with my plasmid and give you them, so now you have more DNA and are thus more adaptive!!!!!!!!!

    Does othat not sound like a penis transfering genes through sperm???

    DO YA LIKE THAT OR WHAT!!!!!!!!!
  5. Jul 5, 2003 #4
    Mentat - Another point I might add is that you must remember the human mitochondria has RNA for a reason. Our mitochondria is actually the mitochondria of the anciet bacteria. In otherwords part of us still contains the elemtns of the ancient bacteria we come from.

    So you can see that there is a direct connection in this matter.

    I bet you're liking how I have been able to answer your questions lately - you know it is nice to be able to spread this information so soon after I first learned it myself!

  6. Jul 6, 2003 #5


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    True in general I suppose, but there are examples of sexual reproduction in "primitive" (less complex) creatures.

    As you found, there is still a lot of research to be done on that question. But as most things, the first critters that could do IT could probably also do it asexually. i.e., the ability arose while the creature was still mostly asexual. As Tyger mentioned, even bacteria can swap genes with other bacteria when the circumstances are right.

    The key is that sexual reproduction gives a big advantage in the form of variety (gene "recombination"). Variety within a population offers more chances at survival when faced with changing environments. In a population of clones (asexual reproduction), Disaster X can wipe out the entire population because they all have the same susceptibility. But in a population with many variations, there is a better chance that some subset of the population will be able to make it through Disaster X. Or, on a more day-to-day level, a diverse population can explore new avenues of living (new foods, new environments, etc.) whereas the clones need things not to change in order to have the odds in their favor.

    I seem to recall hearing about a good reference on this subject just recently...I can't think of it at the moment. If I recall, I'll post it here.
  7. Jul 6, 2003 #6


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    Re: Re: How did sex evolve?

    Greetings !

    Like it was said here before it probably started from
    single cells connecting and sharing DNA. Then it evolved
    into large cells and quick small cells - at least that's
    the way they showed it in one of the Evolution chapters that
    specificly adressed the sex issue.

    One of the intresting experiments that was carried out with
    a species of fish and shown in that chapter showed that
    single sex fish were less capable of fighting off deseases
    because they reproduced by cloning rather than shared genes
    which form a more adaptable system when it comes to viruses
    and bacteria. However, when the gene pool is small the self
    cloning single cell fish had an advantage (which probably
    explains why such a rare spiecies was found in a small pond
    in a desert).

    Live long and prosper.
  8. Jul 6, 2003 #7


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  9. Jul 7, 2003 #8
    One word: Parasites

    If you consider the human genome to be an elaborate set of locks and parasites (eg. virus, bacteria, etc) as safe crackers who are constantly evolving keys to open the locks and exploit it's host. Sexual reproduction is a means of changing the combination of a series of locks every generation. That's the concise version. I recommend you read Matt Ridley's Red Queen. It gives an outline of most of the theories of the origin of sexual reproduction along with an indepth account of how human nature has developed through evolutionary processes. It's a great book.
  10. Jul 7, 2003 #9
    Re: Re: How did sex evolve?

    Fully awesome, CrystalStudios! :smile: I was completely unaware of that.
  11. Jul 7, 2003 #10
    Re: Re: How did sex evolve?

    Ah. That also makes a lot of sense.
  12. Jul 7, 2003 #11
    I'll try and find it, thanks Deslaar.
  13. Jul 8, 2003 #12

    Another God

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    If you want to know anymore about this Mentat, I could hold a small tutorial sort of thread on it (we do a lot of work with this stuff in Microbial Genetics....)

    The Pilus, is often called 'The Sex Pilus', and any cell which expresses this phenotype, actually can't mate with another cell that has pili.
  14. Jul 8, 2003 #13
    I would very much appreciate a "tutorial sort of thread" on this topic, should you find time to do so.
  15. Jul 8, 2003 #14

    one of the most interesting explainations I've heard of, and very credible. It would be nice to see computer sims of some of these ideas run.
  16. Jul 10, 2003 #15
    Evolution of sex.

    I donno Mentat...

    I'm still doing a lot of study on this one!:wink:

    It must have to do with receptors and survival.

    Receptors, even in simple organisms, are there to stimulate an organism and alert it to sources of food and sources of light and sources of dark and sources of DNA (that are outside of its gene pool) with which to hook up.

    The sensors act in the presence of stimulus. Some of the stimulus is adverse and some of it is pleasurable.

    How these distinctions (between pleasurable and adverse) came into being is a long story... I suppose certain cerebral ganglia of the organism lead to a pleasure centre and others lead to a warning system centre... but this is examplified in more complex organisms whereas, in a simple organism (with few ganglia)... there must be a chemical warning system and a chemical pleasure system used to alert the cell group (of the organism) with regard to the stimulus present in its environment.

    Using a similar model we can postulate that a simple organism might experience a chemical surge of a pleasurable content upon realizing the stimulus of one of its own species within its vicinity or environment. The experience is pleasurable... and the result is, possibly, sexual union and offspring that carry a fairly new make up of DNA from both of the original participants.

    From there, sex got a bit more complicated... not quite as "easy" (if you disregard the 60s and 70s) and slightly more creative (when you consider the trapeze and the trampolines in 40 percent of the bedrooms across North America.

    Last edited: Jul 10, 2003
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