penis size and evolution (semen displacement theory, etc.)

Discussion in 'Sex With a Large Penis' started by matthi, Jan 19, 2011.

  1. matthi

    matthi Well-Known Member

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    I was reading Sex at Dawn, where the authors discuss Gordon Gallup's "Semen Displacement Theory".

    The idea is that in a situation where women have many sexual partners in rapid succession, a penis that is shaped to displace semen of other males increases its owner's chances of impregnating her. They have some experimental data to back up this claim, focusing on the diameter of the coronal ridge of the glans as a factor in semen displacement; but they also point out that larger penises in general would have been more effective in such competitive situations (see here for a review).

    As an explanation for why human penises are comparatively large -- to most primate relatives, anyway -- this seems a fine (although not uncontroversial) hypothesis. But, it does require the postulate that for a very long time, women were having sex with many males in short succession. As discussed at length in Sex at Dawn, this does not seem implausible.

    But, I was wondering, are there any other evolutionary explanations (perhaps featuring the female orgasm) for those nice large penises featured on LPSG, and humans in general? Or, are we doomed to ever-decreasing penis sizes, now that the sperm-competition scenario, and thus evolutionary pressure on big and shapely penises according to the theory, is all but eradicated from most societies?
     
    #1 matthi, Jan 19, 2011
    Last edited: Jan 19, 2011
  2. petite

    petite New Member

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    Is that really the only explanation explored in that book? How disappointing. I have heard that theory, but there are others I believe are much more likely.
     
  3. matthi

    matthi Well-Known Member

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    Yes, I like the book a lot, but in my reading the authors don't seem to talk about other explanations (beyond semen displacement) for our big cocks. What did you have in mind, petite? I'm sure others must have considered things like

    - penis size is correlated with behavioral traits that make large penis-wielding males more sexually successful.
    - women prefer to mate with males with large penises.

    (the problem with these explanations is that they introduce a new puzzle, where you now have to explain how that situation came about.)

    - larger penises are more likely to result in female orgasm AND this increases the likelihood of pregnancy.

    (both of these parts of the argument are VERY controversial, as I understand it..)
     
  4. petite

    petite New Member

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    Yeah, I'm not buying the "women were gangbanged sooo much" theory.

    I don't believe female choice had an influence. I believe that other men are more responsible for penis size than women or physical explanations having to do with sex, since throughout most of history women haven't had a choice about who they had sex with, being essentially property or second class citizens. I believe that men who had a higher social status, for whatever reason, be it physical prowess, greater social skills, more wealth (in whatever form), had greater access to mate and/or marry and so they spread their genes more, and men with larger penises were respected more by other men, creating a feedback loop that lead to larger and larger penises. I believe the only thing that limited the size of the penis is whether it would still fit inside the vagina.

    You still see it today in human behavior. Women don't care one-tenth as much as men do about penis size, but men still want to compare and know who is larger and who is smaller than themselves. I've seen really large men in chat become awed and hush their voices when a larger man enters chat, even though the larger man can't hear them! Men still want to see women fucked by penises larger than their own. And as another thread pointed out, an awful lot of men actually enjoy being cuckolded, but women do not.
     
  5. D_Gunther Snotpole

    D_Gunther Snotpole Account Disabled

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    Why, under the same argument would Chimpanzee penises not be equally large? Or even larger, since they are more promiscuous?
    But they're far smaller, roughly half the size of the human penis.

    Interesting theory here, but I'm not sure it passes the sniff test.
     
  6. petite

    petite New Member

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    You're right. Good catch.
     
  7. B_subgirrl

    B_subgirrl New Member

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    I actually think it's a perfectly valid theory. Most primates do a whole lot of gangbanging (never thought I'd use that word in relation to evolutionary psych!), and it's not too much of a stretch of the imagination to imagine that we were doing it too not so long ago.

    Having said that, your theory Petite seems just as valid to some extent. The main problem I see with it is the time frame. Have men been worshiping big cocks for long enough for it to have affected evolution? And were human brains advanced enough to do the worshiping at an early enough time for it to have had such a widespread effect on size?

    matti, did the authors happen to say when they think human penises began to be significantly larger than those of other primates? I mean, I expect there would be little to no evidence on time frame, but it would help if there was.
     
  8. B_subgirrl

    B_subgirrl New Member

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    The same solution is not always found by all organisms for the same problem. There are about a zillion examples of this, but of course, I can't remember a single one right now :redface:.
     
  9. petite

    petite New Member

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    Yet, as Hhuck pointed out, chimpanzees do not have large penises, despite having "gangbanged" for so long, as we know that they do, so that theory seems to hold little water.

    There are many many species that reproduce via a penis, so the theory of convergent evolution would surely mean that more mammals would have larger penises than they do.
     
  10. B_subgirrl

    B_subgirrl New Member

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    I think we posted at the same time!
     
  11. petite

    petite New Member

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    And again! (I added, sorry!)
     
  12. B_subgirrl

    B_subgirrl New Member

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    I think you may have a point with this one.

    Of course, it may have been many factors, rather than just one that combined to enlarge the human penis. Maybe the sperm displacement added an extra 1/8 of an inch. Maybe male penis worship added another 1/8 of an inch. Maybe higher chance of female orgasm added another 1/8 of an inch. Etc.


    :smile: No adding!

    I can't believe I'm talking about evolution on LPSG (and it's not even in Etc)!!!
     
  13. petite

    petite New Member

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    That's not how selective factors in evolution work.

    The way that selection works in evolution is always based on the feedback loop concept, so that the end result taken as far as possible as long as it provides an advantage, [or] until that particular feature is limited by some other evolutionary factor relating to survival or reproductive advantage. Take the peacock. Females selected for a longer tailfeather, which probably initially was a survival advantage, the ability to fly faster, but eventually females who were encoded with the desire for a mate with a longer and longer tailfeather caused the males to develop tailfeathers that were so long that they could no longer fly, and eventually the limiting factor on how long tailfeathers became was how inhibiting those tailfeathers were to their ability to maneuver on the ground, long since having lost the ability to fly.

    Similarly in humans, if females were encoded to desire gang-banging, considering how much freedom we now have, wouldn't modern women be getting gangbanged at a much more frequent rate?

    Instead, there is much more evidence that men are probably encoded to care about their own penis size in relationship to other men, else this board would be totally flooded with women seeking out large penis-ed men, right? Which is another reason why I don't believe that selection by women is what actually created man's large penis, but I digressed from the first point I was making...

    Back to the peacock... If a longer penis provides an advantage, then the penis would get longer and longer until that length is limited by some other factor. In humans, I believe that limiting factor was the lagging size of the female vagina, whose evolution didn't increase in size at as fast a pace. In other species, if a larger penis would provide an advantage, that limiting factor would be something similar and it would work the same way. The penis wouldn't be enlarged just a little bit, it would become enlarged a lot.
     
    #13 petite, Jan 19, 2011
    Last edited: Jan 19, 2011
  14. petite

    petite New Member

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    I should have said, "Back to the peacock... If a longer penis provides an advantage, then the penis would get longer and longer until that length is limited by some other factor or until length no longer provided an evolutionary advantage, in which case you would have to explain why length ceased to work as a method of pushing out competitive semen after such a small change in average penis size."

    Sorry, I have trouble with clarity sometimes when I'm trying to explain an idea.

    (I'm so bad about the editing thing. I'm not trying to trip you up, I just suck at leaving out essential words, like the [or] above, and presenting my ideas in a logical progression. Especially with ideas that I've thought about the most, I don't think of them in a progressive step by step way any more, but rather in a gestalt jumble of all the different ways I've thought about approaching the question at hand in the past, and that interferes with my ability to explain what I mean. I'm much clearer at explaining my thoughts when it's the first time I've thought of an idea, because then my logic progresses in a step by step manner and I can simply record my stream of conscious thoughts and it's much clearer to follow.)
     
    #14 petite, Jan 19, 2011
    Last edited: Jan 19, 2011
  15. wilko

    wilko Member

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    I agree with this. As humanoids evolved a capacity for symbolism, a large penis perhaps became symbolic of high masculinity and thus a way of establishing heirachy among males.
     
  16. B_subgirrl

    B_subgirrl New Member

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    Ah, maybe I wasn't clear enough. I didn't intend to convey that each factor made things a little bigger, then thought 'I'll stop there, that's enough'. I meant that each of the factors could have been working SIMULTANEOUSLY, with all sharing the same limiting factor (possibly vagina size).

    Which brings me to another thought . . . it could be that the larger penis is only a side effect of a large vagina (haven't seen any research on it, just sort of thinking out loud here). Maybe, as the vagina (and other female organs) grew larger to work with bipedalism and comparatively large-headed babies, the penis had to grow apace. Shorter penises wouldn't have been depositing their sperm as deep as the longer penises were, and girthier penises may have left less space for sperm to escape before being taken into the uterus than thinner penises. So large penises are just a side effect of large vaginas. Maybe.


    We lost the gangbanging gene along the way :tongue:.


    I agree. I actually quite like your theory. I'm just not sure if the time factor is there.
     
  17. petite

    petite New Member

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    While possible, I feel that it's a very remote possibility. I think there's too many ifs there without enough positive evidence to support it.

    Interesting! I'm speaking of your interesting supposition that the female vagina could have increased in size as a result of bipedalism and the penis needed to keep up in size... I've actually thought of this! Not the bipedalism explanation for an increase in vaginal size, which is an impressive bit of creative thought, but whether vaginal size might have preceded penile size. The problem is, the cervix isn't located at the very end of the vagina, which eliminates the argument that longer penises are required for implantation in human females. Also, if implantation were the driving factor, then the cervix would become closer and closer to the opening of our bodies. It's those who reproduce the most who pass on their genes, so it would more advantageous to be fertilized more easily and not the other way around. Although, now that I think about it again, supposing that vaginal size increased before penile size thus driving penile growth up, both an increase in penile size and the movement of the cervix towards the opening of the vagina could occur simultaneously without any flaw in logic... [But then why did penile growth continue to grow past the necessary size for fertilization once the cervix becomes so easily accessible by shorter penises? There is no longer the evolutionary advantage that would continue the feedback loop that would generate longer penises. I realize looking at it now that my logic failed me when I wrote that last sentence. One mechanism would end up taking over and the other would stop.] But now that I think about how the uterus operates within the bodies of women, the cervix was probably always close to the opening. When I was pregnant, there was definitely no more room inside my torso for my cervix to be located higher up inside my body!

    In fact, if the cervix were located at the very end of the vagina, it would cause more maternal deaths because of the extremely large size of human heads. Our cervixes are actually closer to the opening of our bodies, reducing the amount of vaginal tearing during childbirth and a living mother has a better chance of passing on her genes again.

    :lmao:

    That's fair! As you always are! :biggrin1:
     
    #17 petite, Jan 19, 2011
    Last edited: Jan 19, 2011
  18. B_subgirrl

    B_subgirrl New Member

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    No worries :smile:. I'm worse than you are at explaining things when I'm not in uni-think mode (which I'm evidently not :redface::tongue:). I've read a whole bunch of stuff on evolution, and never quite get around to processing it as a whole, so you never know what's gonna come out :redface:.

    And definitely not worried about being tripped. It's not a competition - this is just fun to think about!!!
     
  19. petite

    petite New Member

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    That's an excellent way to explain it. I was struggling to find the words to express this particular thought and you did it so much more concisely than I could have.
     
  20. petite

    petite New Member

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    I totally agree. It's the reason why I've always loved science. It's fun to think about.
     
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