NCBI ROFL: An explanation for the shape of the human penis.

By ncbi rofl | January 28, 2011 7:00 pm

“The present form of the human penis, reached over several million years of evolution, was orchestrated by the vagina of the human female.  The multifunctional vagina serves as a birth canal, a component of the structural support for the internal pelvic organs, and as a coital organ. In this last function, it has had an evolutionary effect in shaping male sexual anatomy.  Hominid fossils so far discovered show that the female pelvis evolved to accommodate the increasing size of the brain of the human infant.  Larger cranial capacity necessitated a larger birth canal and, as a result of sexual selection, an increase in the size of the penis.  Compared to that of the other great apes, the human penis is considerably larger, and evidence suggests that its unique configuration may also be a result of vaginal influence.

It has been proposed that the shape of the glans with its distinctive corona facilitates the scooping out of previously deposited semen, enabling the subsequent deposition of other genetic material.  This is not a likely occurrence.  The healthy vagina has a low pH to protect it from invading organisms.  This intense acidity will kill all sperm not promptly reaching the safety of the cervical mucus.  I suggest the evolutionary function of the glans and its corona is not to scoop out semen but vaginal secretions, which are then absorbed by the encompassing foreskin.  The mucous membrane of the foreskin adjacent to the glans is highly absorbent, as evidenced by the increased susceptibility of the uncircumcised male to HIV.  It has been suggested that there may be a glans protecting feature of the foreskin, but it is entirely possible that its primary function is to absorb behavior modifying chemical messengers from the female.  Numerous studies have shown the vaginal mucosa to be secretory.  In the primate rear-approach coital position, the corona rubs against the anatomically posterior wall of the vanina, the most dependent surface when the woman is standing, and therefore the place more likely to collect vaginal secretions.  The deepest end of the posterior vagina is the cul de sac, which commonly contains a small amount of fluid.  An analytical study of the vaginal secretions of an ovulating female for neuropeptides, such as pitocin and vasopressin, known to enhance pair bonding and protective behavior in the male, could be revealing.  Sexual intercourse may be a medium of communication between humans older than language itself.”

Image: Failblog

Related content:
Discoblog: NCBI ROFL: Phantom penis: historical dimensions.
Discoblog: NCBI ROFL: Wham, bam, thank you ma’am: an evolutionary perspective.
Discoblog: NCBI ROFL: Does semen have antidepressant properties?

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CATEGORIZED UNDER: NCBI ROFL, penis friday, Top Posts, WTF?
  • d

    I do seem to remember that as a child when I “cleaned” myself in the shower I could taste the soap. It wasn’t overpowering but it was there.

  • matt

    Perhaps the rifle is more accurate than the pistol. I for one am thankful i have a rifle that shoots that extended accurate distance.

  • VJGoh

    Does it really have to be one or the other? Sperm competition isn’t exactly far-fetched or unique. If the penis dislodges semen AND works to displace acid vaginal fluid, that hardly seems crazy. The only reason one would speculate on one and not the other is to have a go at the idea of sperm competition and the possibility of a non-monogamous, competitive/social mating scheme and the anthropological and sociological consequences therein.

    One-or-the-other theories bug me because they establish a false dichotomy that insists that the fully formed chicken MUST have come before the fully formed egg (or vice-versa, I suppose), instead of allowing for a proto-chicken evolving to lay a proto-egg and iterating on that. :/

  • Curious

    If the foreskin membrane absorbs behavior modifying compounds, the circumsicion could be originally conceived to avoid the female induced bonding on a context of patriarchal society?

  • Chris

    It’s very simple. Tab A fits into Slot B.

  • fredo

    “it is entirely possible that its primary function is to absorb behavior modifying chemical messengers from the female” – does this mean that women’s brains are controlled by mucus in their vaginas? That’s the first I’ve heard of that.

    Also I like that “it is entirely possible” translates to “I have just imagined”…

    I always imagined the ‘knob-end’ (as it is known in some circles) serves to provide sensation to both parties. If the penis was completely smooth there would not be much friction.

  • Anonymous

    I wish I still had my foreskin.

  • Gokumaan

    You mean tab “I” fits into slot “U”

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About ncbi rofl

NCBI ROFL is the brainchild of two Molecular and Cell Biology graduate students at UC Berkeley and features real research articles from the PubMed database (which is housed by the National Center for Biotechnology information, aka NCBI) that they find amusing (ROFL is a commonly-used internet acronym for "rolling on the floor, laughing"). Follow us on twitter: @ncbirofl

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