Human penis more evolved?

[Pirogi]

I read this in What Your Doctor May Not Tell You About Circumcision, and I had never heard it before. The authors said that the human penis (or I guess, more accurately, the foreskin) is more evolved than those of lower primates. The reason they gave was because the human foreskin has more (Meissner's?) corpuscles in the foreskin, and less in the glans, than other primates. Or actually, I guess the point was that humans are more evolved than primates, so the human penis/foreskin must therefore be more evolved as well, and so the specific distribution of mechanoreceptors must therefore be optimal. It was a really strange point to make.

When looking around the web for more info, I had a hard time understanding what I was reading. It looks like there are other types of mechanoreceptors as well. Can someone who knows chime in and tell me if my understanding is correct?

- Meissner's corpuscles are rapidly adapting tactile mechanoreceptors that detect light touch - stroking, fluttering, etc.
- Pacinian corpuscles are rapidly adapting tactile mechanoreceptors that are deeper in the tissue and detect gross pressure changes and vibrations - harder touch, like a poke.
- Merkel's discs are slowly adapting tactile mechanoreceptors that detect steady pressure
- Ruffini corpuscles are slowly adapting tactile mechanoreceptors that detect stretching of the skin

There are also many types of free nerve endings that detect touch, pressure, skin stretch, temperature, and pain.

Apparently (and I have no reference for this ... does anyone else?) Pacinian corpuscles are found in larger numbers on the glans than Meissner's corpuscles, and therein lies the controversy. People who oppose circumcision play up the Meissner's corpuscles angle (more on the foreskin, less on the glans), and those who support circumcision point to the Pacinian corpuscles on the glans to support that there is still plenty of sensation left in the glans when the foreskin is cut off. And really, is it possible to qualitatively support one type of mechanoreceptor over another, for every person? ie, one person may enjoy light touch more than harder touch, but others may enjoy the opposite. Is one type of mechanoreceptor "better" than the other?

The idea in the book that the evolved human has a "better" foreskin was strange to me. Anybody else have thoughts on this? I hadn't seen much info about mechanoreceptors/nerve endings in the different parts of the penis before this.

[Greg B]

I have not read that book, but from what you say, I would be cautious about using the phrase "more evolved" or "more advanced from an evolutionary standpoint."

There are plenty examples, for instance, of evolution where something is reduced or even lost.

The key to understanding how to interprete what the author may be saying is to have a soldi definition of what he means by "more evolved". Many do not really understand evolution and how it works. And we are still refining our scientific understanding.

Regards

[brant31]

Originally Posted by Pirogi

And really, is it possible to qualitatively support one type of mechanoreceptor over another, for every person? ie, one person may enjoy light touch more than harder touch, but others may enjoy the opposite. Is one type of mechanoreceptor "better" than the other?

The idea in the book that the evolved human has a "better" foreskin was strange to me. Anybody else have thoughts on this? I hadn't seen much info about mechanoreceptors/nerve endings in the different parts of the penis before this.

As it has been explained to me by doctors and a neuroanatomist, the glans is a relatively "dumb" organ... it can detect when it is being stimulated, but not how, from what, or how much. In relative terms, it is less sensitive than the heel of the foot. Think of its sensation as one low, mournful note vs the lively and varied symphony of the inner foreskin. I don't think nature ever intended the glans to be the primary sense receptor and interpreter on the penis... it is a useful shape for insertion, and the corona is probably shaped the way it is in great part to stimulate the foreskin as it passes over.

It has been said that the glans can live without a foreskin, but the foreskin cannot live without the glans. This is because another major reason the glans is present and shaped the way it is, is to keep the foreskin moderately stretched and supple. It is rather like a shoe tree. For years I automatically bought into the idea that the foreskin protects the glans, until one day in my research I had an epiphany: the foreskin is so much more important, and the glans is primarily there to serve the foreskin. People have it mostly backwards.

The analogy I use most often is the ancient practice of washing clothes against a rock. The glans is the rock, of course, and the foreskin is the object of the exercise -- also the valuable bit of the exercise.

Dr Chris Cold of Marshfield Clinic in Wisconsin and Prof Ken McGrath of Auckland University of Technology did research together and were able to conclude that the human foreskin is far from vestigial, as many detractors claim. To their surprise, in fact, it has been growing longer and more complex over tens of thousands of years, its evolution quickly outstripping that of other primates. No matter how many we cut off, Mother Nature keeps coming back to remind us how integral the foreskin is to healthy and enjoyable reproduction of our species. Longer foreskins apparently also serve a protective function from morbidity; the more moist mucosal tissue we have at our genitals, the greater and more effective the barrier against bacterial and viral infections.

I wouldn't get too caught up in the different types of nerve endings, other than to note that they work best in concert. Lots of men will tell you anecdotally that their glans is the most sensitive part of their penis, but histology does not bear that out in the least. For most circumcised men it is the spot on the ventral penis where the inverted frenulum remnant meets the circumcision scar, and for most intact men, it is the frenulum and the rest of the inner foreskin -- whether they've bothered to isolate the sensation or not.

[tlh]

Have you seen this article?


http://www.cirp.org/library/anatomy/taves1/

The intromission function of the foreskin.


Masters and Johnson observed that the foreskin unrolled with intercourse. However, they overlooked a prior observation that intromission was thereby made easier. To evaluate this observation an artificial introitus was mounted on a scales. Repeated measurements showed a 10-fold reduction of force on entry with an initially unretracted foreskin as compared to entry with a retracted foreskin. For the foreskin to reduce the force required it must cover most of the glans when the penis is erect. This may occur only in humans. These observations mean that foreskin and prepuce can no longer be considered synonymous. Why the penises of humans and chimpanzees evolved so differently should be addressed in light of these findings.

[QueenOfTheMeadow]

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