Elsevier

Medical Hypotheses

Volume 59, Issue 2, August 2002, Pages 180-182
Medical Hypotheses

The intromission function of the foreskin

https://doi.org/10.1016/S0306-9877(02)00250-5Get rights and content

Abstract

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.

Introduction

Morgan [1], [2] stated that vaginal intromission is easier with a (retractable) foreskin in place. However, no one has experimentally tested his contention or clearly explained the mechanism. There are no contradictory claims in any of the citations to Morgan's letters. Harnes (3) published a `fruitless' attempt with a questionnaire to evaluate Morgan's claim of greater sexual pleasure with a foreskin. Articles about circumcision and evolutionary antecedents of human sexuality have almost totally neglected the even more general question: the function of the foreskin. The recent position paper of the American Pediatrics Association is silent on this issue (4). A heated debate in the New England Journal of Medicine produced no references and only a single sentence regarding the function of the foreskin, `...protection of the sensitive glans' (5). Porter and Bunker (6) in an article entitled, The dysfunctional foreskin, say only `...its function – physically, physiologically and immunologically protective of the glans and external urethral orifice.'

Several recent publications have considered evolutionary antecedents of human sexual behavior and unusual primate male genitalia but they do not mention the foreskin or prepuce [7], [8], [9]. Money (10) cites a survey finding that the foreskin is a `visual and tactile erotic organ.' Cox (11) postulates, without evidence, that the foreskin retards the age of sexual reproduction. There is little in the older literature they missed. Even in an article entitled, `Observations on the evolution of the genitalia and copulatory behaviour in male primates, (12) there is no mention of the foreskin or prepuce! All the Textbook of Sexual Medicine (13) says, without references, is `There is much controversy and little data surrounding the question of the effect of circumcision on male function.'

Section snippets

Evidence

Preliminary measurements of the force required for intromission with and without the benefit of the foreskin have been made with a simple device. The device consisted of a Styrofoam cup the bottom of which was cut to make a flexible artificial introitus. The cup was mounted on a diet scales so that the force being applied could be noted (Fig. 1). Twelve measurements were made with the glans penis alternately exposed or covered by the foreskin. Intromission with the glans exposed required a

Discussion

These preliminary findings support the claim by Morgan [1], [2] that vaginal intromission is easier with a (retractable) foreskin in place. The mechanism is simple. The interposed foreskin decreases the friction between the introitus and the glans. The unretracted foreskin consists of a thin dermis that is folded on itself with very little friction between the layers. As the penis advances, the foreskin unrolls so that the portion that makes initial contact with the introitus is 6 cm. Up the

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      Miscellaneous findings can be used to suggest potential mechanisms by which circumcision may impact competition for fertilizations. These include increased effort required to overcome friction during intromission (Taves, 2002); desensitization of the penis, raising the threshold for sexual arousal (Immerman & Mackey, 1997; Sorrells et al., 2007); increased latency to ejaculation (Senkul et al., 2004), which would especially hinder hasty covert copulations; decreased stimulation of the female, potentially impacting cryptic choice (O'Hara & O'Hara, 1999); an 8-mm decrease in mean length of the erect penis associated with circumcision (Richters, Gerofi, & Donovan, 1995); elimination of sex pheromones produced by the preputial mucosa (Immerman & Mackey 1997); and disruption of neural feedback involved in adaptive modulation of copulation dynamics (Cold & Taylor, 1999). These mechanisms are wholly speculative, based on limited observations.

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