Published May 15, 2018
Updated August 8, 2022
How a bizarre study exposes the intellectual laziness of circumcision scholars
“You have to know how to read a scientific paper—and actually bother to do it.” 
In 2002 Donald R Taves, a psychiatrist at the University of Washington, conducted an experiment to measure the effect of foreskin on the force necessary for vaginal penetration. He reported his experiment in a medical journal.  The study provides a shocking view into the state of scholarship and confirmation bias among academics, particularly those with an anti-circumcision agenda.
Taves cut a quarter-size hole in the bottom of a Styrofoam cup to simulate a vaginal opening. He mounted the cup on a diet scale to measure the force needed for a man to enter his partner's vagina.  The 76 year-old Taves penetrated the hole with his erect penis - six times with his glans exposed, and six more times with his foreskin covering the glans. 
Taves described penetration with his foreskin covering the glans as "comfortable", while penetration with his foreskin pulled back and his glans exposed was "uncomfortable". He concluded that circumcised men use ten times greater force to enter a female partner than their uncircumcised peers.
The experiment consisted of the researcher having sexual intercourse with a Styrofoam cup. The problems with this study (I use that term loosely) are so numerous and apparent, it’s difficult to know where to begin.
Vaginas come in different sizes. So do penises. The researcher measured force based on only one penile girth and only one size opening.
Several factors can affect the force necessary for penetration: body angles, the mood of the male, the mood of the female, their levels of sexual arousal, their ages, and the point in the woman’s menstrual cycle. None of these aspects was measured. In fact the researcher never considered any factor other than his own foreskin.
Putting an exposed glans through the rough edges of a Styrofoam hole may be uncomfortable, even painful. A vaginal opening, by contrast, is smooth, somewhat flexible, and naturally designed for comfortable penetration.
The subject’s penis rubbed against the side of the cup as it entered and withdrew. But a vaginal canal is significantly longer than the 1/4-inch edge of a cup. The vagina puts pressure on most of the penis as it penetrates and withdraws, providing pleasurable sensations leading to orgasm.
A sexually aroused woman secretes vaginal fluid that aids intercourse. But a Styrofoam cup provides no such lubrication, and the researcher didn’t indicate whether he used artificial lubrication.
The assumption seems to be that less force and friction during penetration are preferable. But friction between the male and female genitals – the contact of the penis with the vaginal canal – is what causes stimulative pleasure. Many women have reported that the most important physical factor in a partner’s genitals is his girth.
"The British research … confirmed that women do indeed prefer a thick penis. The reason: ‘The greatest number of nerve endings are in the lowest part of the vagina,’ Nicole says. ‘So when a thick penis pushes against the labia and lower vaginal walls, it provides intense, pleasurable sensation.’” 
The male researcher had total control over penetration. But a number of sexual positions allow the female to control the depth, angle, and pace of penetration. 
While a thinner penis would provide less friction entering the vagina, a thicker penis that rubs against the vaginal wall might provide greater pleasure for both male and female partners. A lack of friction would cause the least amount of force. But such a sexual experience may be considered unsatisfying.
These flaws don’t begin to cover the problems associated with Taves using himself as the sole subject. Without a baseline measurement, the results can’t be compared. The researcher might have inadvertantly altered the amount of force he used during successive insertions. And with only a single participant, the results are not applicable to the general population. 
There is no legitimate comparison between the experiment and human sexual intercourse. A middle school student who submitted this experiment for a school project would receive a failing grade. One is left speechless at the realization that this study is given any consideration.
And yet, astonishingly, the study has been given serious respect in the scientific community. The results have been cited in at least 40 scholarly papers, articles, books, presentations, and anti-circumcision websites. Academics with advanced degrees have cited the study to prove that foreskin plays an "important" or even an "essential" role "in the dynamics of sexual intercourse.” At least eight papers claim that the study proves that circumcision increases the force necessary for vaginal penetration by 90% or ten-fold - despite the fact that not one vagina or circumcised penis was involved in the study.
Academic sources in Australia, Canada, India, and four European countries demonstrate that the study has broad international acceptance. The KNMG, a medical organization representing 53,000 physicians in the Netherlands, claimed that the study shows that circumcision impairs male sexuality - in order to support the KNMG's position against circumcision. Some writers cited the study as evidence that circumcision harms masturbation, reduces male sexual pleasure, and increases vaginal pain - subjects that Taves did not explore. In most cases this was the only study cited in support of the assertion that circumcision increases the difficulty in vaginal intromission. An appendix at the end of this post documents the academic sources that cite the study.
Confirmation bias is the tendency to seek out and embrace information that supports one’s view while ignoring or dismissing information that casts doubt on one’s perspective. “Deliberate use of confirmation bias is held in low esteem by scientists, and allowing confirmation bias to get the better of your results is regarded as a particularly sad form of incompetence.”  Scholarly acceptance of this study is one of many examples of researchers with a clear anti-circumcision agenda showing little or no skepticism for studies that support their views. One wonders how many researchers don’t even bother to read a study, but just blindly report the descriptions they read from earlier papers.
Based on the demonstrated confirmation bias and lack of skepticism on the part of both pro-circumcision and anti-circumcision researchers, any study related to this topic shouldn’t be accepted at face value. Each paper should be analyzed with a degree of skepticism. Having reviewed several studies related to circumcision, I have discovered to my amazement that studies are cited primarily based on whether the results support a scholar’s agenda, and not based on whether the scholar has affirmed that a study is scientifically valid and relevant.
Any partisan who cites the Taves study should answer whether he reviewed the study. If the answer is yes, he must explain why he considers an experiment that consists of sex with a Styrofoam cup would provide any information about the effect of circumcision on vaginal intercourse. If the answer is no, he must explain why others should give credence to the work of a researcher who doesn’t bother to research. We must call to account those scholars who are too lazy to do even a basic review of supportive evidence.
I didn't write this article in order to ridicule Donald Taves. The effect of the foreskin on the force used during vaginal penetration can be an appropriate topic for a researcher to explore. In principle Taves or a colleague should be able to test his hypothesis more rigorously. An adult toy such as an artificial vagina might effectively simulate the proper resistance during penetration. If several circumcised men and uncircumcised men can be recruited to participate, perhaps an experiment could be devised to measure intromission force.
That said, science-based studies in Africa have already shown that circumcision does not affect ease of vaginal penetration. Two RCT (randomized controlled trial) studies found no significant differences between circumcised men and uncircumcised men.  In a third study of female partners of recently circumcised men, 3.5% of women reported a decreased difficulty of vaginal penetration following circumcision, while less than 0.5% reported an increased difficulty. 
My contempt is reserved for the scholars who blindly cited the study. One wonders how many of them bothered to read a description of the experiment. They may have assumed that the study is valid based on previous citations or its publication in a science journal. They may have assumed that it’s valid because the results support their agenda. One would expect that academics know intuitively that a hole cut out of a Styrofoam cup is no substitute for a real woman. Alas, one learns with chagrin that society sometimes places too much faith in the wisdom and diligence of the academic science community.
 John Bohannon, “I Fooled Millions Into Thinking Chocolate Helps Weight Loss”; io9; May 27, 2015
 Donald R Taves; “The intromission function of the foreskin”; Medical Hypotheses, pp 180-182; August 2002
 A photo caption: Devise for measuring penile force during intromission. (Diet scales, Hanson Scale Co….) Lower left: an artificial introitus was made by cutting a quarter size piece out of the bottom of the an [sic] 8 1/3 ounce foam beverage cup (Western Family Space Saver insulated FOAM CUPS…) and making 8 equidistant cuts from the margin to the thickened rim of the cup. The length and number of cuts determined the stiffness and expansibility of the ‘introutus’ and hence the ease of intromission.
 Donald Taves; email to Andrew Gross; December 5, 2016. "I was the only subject. The comparison was the force needed for intromission of the artificial entroitus (the opening in the cup) when my foreskin was retracted as compared to when it was in place."
 Brittany Risher and Justin Park; “How big is yours?”; Men’s Health; January 29, 2010
 Anna Borges; “7 Sex Moves That Put YOU in Control”; Women’s Health; November 5, 2014
 Mark Sisson; “The Pitfalls and Limitations of Self-Experimentation”; Mark’s Daily Apple; 2015
 Chris Lee, “Confirmation bias in science: how to avoid it”; Ars technica; July 13, 2010
 Godfrey Kigozi et al; "The effect of male circumcision on sexual satisfaction and function, results from a randomized trial of male circumcision for human immunodeficiency virus prevention, Rakai, Uganda"; BJU International; December 7, 2007
 John M. Krieger et al; "Adult Male Circumcision: Effects on Sexual Function and Sexual Satisfaction in Kisumu, Kenya"; Journal of Sexual Medicine; August 28, 2008
 Godfrey Kigozi et al; "Sexual satisfaction of women partners of circumcised men in a randomized trial of male circumcision in Rakai, Uganda"; BJU International; November 10, 2009
Studies, articles, and websites that cite “The intromission function of the foreskin”
1."Taves, D., 'The Intromission Function of the Foreskin.' Med Hypothesis 59 (2002): 180." Academic Research Library - A categorized collection of academic articles and resources on foreskin and circumcision, Foreskin anatomy and functions; Your Whole Baby; page updated June 3, 2021. Entry includes a link and an excerpt from the abstract: "...Repeated measurements showed a 10-fold reduction of force on entry with an initially unretracted foreskin as compared to entry with a retracted foreskin..."
2. The intromission function of the foreskin; Circumcision Reference Library (published the entire paper)
3. Hill, George; “Can Anyone Authorize the Nontherapeutic Permanent Alteration of a Child's Body?”; American Journal of Bioethics; 2003 "The foreskin plays an essential role in the dynamics of sexual intercourse, enabling nontraumatic intromission (Taves 2002)”
4. Fox, Mary; “A covenant with the status quo? Male circumcision and the new BMA guidance to doctors; 2005”; Journal of Medical Ethics; 2005 “The prepuce is a complex structure that has a range of significant sexological functions playing ‘an important role in the mechanical functioning of the penis during sexual acts, such as penetrative intercourse and masturbation.’” [citing Taves from other sources]
5. Elke D. Reissing, PhD.; "Pain, Fear, and Avoidance: Why a woman's body says no to sex"; Presentation given in part at the 2006 annual conference of the Canadian Psychological Association; University of Ottawa. "the elongated foreskin in men as a mechanical facilitating intromission" [citing Taves and a 1999 Cold-McGrath paper that discusses the genitalia of primate animals.] the elongated foreskin in men as a mechanism facilitating intromission
6. Dalton, JD; “Male circumcision - see the harm to get a balanced picture”; Journal of Men's Health and Gender. 2007 “Male circumcision permanently removes normal, functional, specialised tissue. It removes … the normal gliding function that facilitates intromission.” [citing Taves]
7. Dalton, John D; “Effect of circumcision on intromission and sexual satisfaction”; BMJ; 2007 “The intromission function of the foreskin has been documented by Taves.”
8. Hill, George; “The Case Against Circumcision”; Journal of Men’s Health & Gender; 2007 “The force required to penetrate increases 10-fold when the foreskin is absent.” [citing Taves]
9. Wilson, Christopher G; "Male genital mutilation: an adaptation to sexual conflict"; Evolution and Human Behavior; May 2008 "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)”
10. "Genital Integrity Policy Statement"; Doctors Opposing Circumcision; June 2008. "In adult life, the gliding action facilitates introitus."
(NOTE: The authors assigned footnote #4 to this statement. However footnote #4 refers to an article that does not mention introitus or intromission. Footnote #17 refers to Taves. The statement assigned to footnote #16 precedes this statement, and the statement assigned to footnote #18 follows shortly thereafter. It is therefore reasonable to conclude that the authors assigned the wrong footnote to the quoted statement.
11. Schreiber, M; Juristische Aspekte der rituellen Zirkumzision; Klinische Pädiatrie; 2009 “In einem Experiment wurde gezeigt, dass eine fehlende Vorhaut beim Einf ü hren des erigierten Penis die Reibekr ä fte um den Faktor 10 steigern kann.” [citing Taves] TRANSLATION: “In an experiment it was shown that the lack of foreskin when introducing the erect penis can increase the force of friction by a factor of 10.”
12. Gillian E. Langley; "Framing the foreskin: A content analysis of circumcision information handouts for expectant parents", p 82; University of Colorado Denver; 2009. "The evidence on the sexual functionality of the foreskin comes not only from anatomical and touch-testing studies such as those discussed above, but also from ... studies of effects on lubrication and intromission..." [citing Taves along with three studies that were based on inferior methodology - O'Hara & O'Hara (1999), Bensley & Boyle (2001), Bensley & Boyle (2003).]
13. Prof. Dr. Arie Nieuwenhuijzen Kruseman; "Non-therapuetic circumcision of male minors"; Koninklijke Nederlandsche Maatschappij tot bevordering der Geneeskunst (KNMG); May 27, 2010. "Another part of this argument says that [non-therapuetic circumcision] does not affect male sexuality. The foreskin is regarded as a part of the body that has no function at all in male sexuality. Many sexologists contradict this idea: in their view, the foreskin is a complex, erotogenic structure that plays an important role ‘in the mechanical function of the penis during sexual acts, such as penetrative intercourse and masturbation.’" [citing Taves from A Covenant with the Status Quo?]
14. Duncker, Richard; "A controversial junction between politics, religion, science and sex"; Men Do Complain; November 9, 2010. "The foreskin has been present in mammals for about 65 million years to aid sexual intercourse because the mechanical function of the foreskin reduces the force needed for the insertion of the penis into the vagina, intromission, by a factor of 10." [citing Taves]
15. Warwick Marshall; "Circumcision in Australia: Reforming the Law", pp 30-31; University of Tasmania; April 2011. "An unaltered foreskin has some accepted, and several disputed, beneficial functions affected by circumcision: ... it may help facilitate and reduce trauma to the vagina during intromission..." [citing Taves along with several studies by longtime anti-circumcision activists O'Hara, Denniston, Milos, Taylor, Boyle, and others]
16. Bunker, C.B.; “The Genital, Perianal and Umbilical Regions”; Andrologia; 2010 Song, B; “Possible function of the frenulum of prepuce in penile erection”; Andrologia; November 29, 2011. "The frenulum of prepuce is the ruffle of the foreskin, while little is known about its function." [citing Taves]
17. Hegazy, Abdelmonem Awad; “Male circumcision: review and authors perspective”; theHealth; March 2012 “Moreover, the foreskin that is retracted over the body of the glans during coitus facilitating the intromission.” [citing Taves]
18. Schröder, Annette; “Circumcision: Case Against Surgery Without Medical Indication”; Frontiers in Immunology; May 2012, p 188 “An experimental study showed that the foreskin, being a double invagination of skin that covers the glans and unfolds with intromission, facilitates intromission significantly (measured by force in g) compared to the exposed glans.” [citing Taves]
19. E. Bondioli; "Preliminary data for the development of a decellularized membrane from animal dermis"; Journal of Tissue Engineering and Regenerative Medicine; April 2014. "Circumcision also alters the mechanical functioning of the penis, requiring a ten-fold increase in force to achieve vaginal penetration." [citing Taves]
20. Njoroge, Kezia Muthone; "Male circumcision and the shaping of masculinities in Muranga, Kenya: Implications for public health"; Northumbria University; December 2014. "The penetrative force is argued to increase ten times when the foreskin is absent (Taves, 2002)."
21. “Rook’s Textbook of Dermatology; Griffins, Christopher et al, editors; Wiley; 2015 [citing Taves]
22. Denniston, George; "Male Infant Circumcision: A Brief Overview of the Issues"; Doctors Opposing Circumcision; February, 2016 “Circumcision has been shown to increase the difficulty of penetration” [citing Taves and a 2004 article about erectile dysfunction following adult circumcision]
23. Arianne Shahvisi; "Cutting slack and cutting corners: anethical and pragmatic response to Arora and Jacobs’ 'Female genital alteration: a compromise solution’"; BMJ Medical Ethics; March 2016 "The foreskin is a richly innervated, highly mobile piece of tissue that plays an important mechanical role in masturbation and in other sexual acts. Unsurprisingly then, circumcision has been shown to limit the sexuality of boys and men." [citing Taves]
24. Esra, RT; “Does HIV Exploit the Inflammatory Milieu of the Male Genital Tract for Successful Infection?”; Frontiers in Immunology; June 2016 “Although not necessary for normal penile functioning, the foreskin is thought to confer physical and immunological protection to the sensitive glans penis.” [citing Taves]
25. J. Steven Svoboda et al; “Circumcision is Unethical and Unlawful”; Cambridge University Press; summer 2016. “The foreskin protects the glans against dryness and abrasion, and allows for a unique gliding action that may facilitate comfortable sexual intercourse.” [citing Taves and three other sources]
26. Arianne Shahvisi; "Why UK doctors should be troubled by female genital mutilation legislation"; Clinical Ethics; December 2016 [citing Taves in the references]
27. J. Stephen Svoboda; “Nontherapeutic Circumcision of Minors as an Ethically Problematic Form of Iatrogenic Injury”; AMA Journal of Ethics; August 2017 “The foreskin keeps the glans moist and facilitates a gliding action that promotes pleasurable sexual sensations.” [citing Taves] 28. Lindsay Watson and Tom Golden; "Male Circumcision Grief: Effective and Ineffective Therapeutic Approaches"; New Male Studies: An International Journal, p 111; August 24, 2017. "In reality, the foreskin ... reduces the force needed to penetrate the vagina - the 'shoehorn effect' (Taves, 2002)..."
29. Jonathan I. Meddings; "Genital Autonomy (Rationalist Society of Australia White Paper)"; Rationalist Society of Australia; February 2018 "The foreskin facilitates the insertion of the penis into the vagina, and circumcision increases the force required for penetration tenfold." [citing Taves]
30. Stefano Eleuteri; "Mutilazioni genitali: diffusione, significato e gestione clinica"; April 2018; "È richiesto un maggiore attrito penieno durante la penetrazione (Taves, 2002)" TRANSLATION: "Increased penile friction is required during penetration (Taves, 2002)"
31. Morris L. Sorrells; "The Sexual Impact of Circumcision"; Doctors Opposing Circumcision; last updated April 2018 "The mobility of the intact penile skin also plays a facilitative role in foreplay, masturbation, and intromission (insertion of the penis), all of which are adversely impacted by circumcision." [citing Taves and a 2007 study of men circumcised as adults]
32. Munzer, Stephen R.; Examining Nontherapeutic Circumcision; Health Matrix: The Journal of Law-Medicine; May 17, 2018. "The foreskin, mucous membrane covering the glans, and the frenulum have at least the following functions: protection of the glans from injury; protection of the glans and the opening of the urethra (urethral meatus) from chafing and contaminants (dirt, sand, etc.); lubrication of the glans during sexual arousal to facilitate intercourse and masturbation; and erogenous sensation." [citing Taves and others]
33. Venkatachalam Raveentheran; “Reply to Letter to the Editor”; Journal of Pediatric Surgery; June 1, 2018. “Donald Taves hypothesized that rolling back of intact prepuce during intermission makes penile penetration easier. According to him friction caused by circumcised glans and the ensuing discomfort is probably an impediment to intercourse. If so, primitive man should have performed circumcision on young boys rather than in late adolescence as a gesture of coital facilitation.” Stephen Moreton engaged with Raveentheran, and concluded, "[Raveentheran] also misses my point about Taves' experiment. As I said, a Styrofoam cup is not a model for a human vagina, and Raveethiran's hair-splitting over "intromission" and "intercourse" does not change this. Circumcision does not make "intromission unpleasant..." Stephen Moreton; "A critique of Raveethiran's 'Reply to letter to the Editor: Tracing the origins of circumcision'"; Journal of Pediatric Surgery; January 21, 2019
34 Welch, Stephanie; "The 'Benefits,' Risks, and Costs of Routine Infant Circumcision"; Journal of Evolution and Health; July 19, 2018. "The retraction of the foreskin allows the penis to function as a rolling bearing in which the male and female mucosal tissue can come in direct contact while the epithelial tissue remains outside (and lubrication stays inside). This reduces the force needed for intromission by 90%." [citing Taves]
35. Arianne Shahvisi; "Female Genital Alteration in the UK: A failure of pluralism and intersectionality" - in: Katja Kuehlmeyer, et al (editors); "Ethical, legal and social aspects of healthcare for migrants: perspectives from the UK and Germany", p 216; Routledge; November 2018. "While FGA is often described as being intended to control and limit the sexuality women, male circumcision is almost never described in this way, even though it has been shown to limit the sexual pleasure of men (Taves, 2002)."
36. Valeria Purpura; "The development of a decellularized extracellular matrix–based biomaterial scaffold derived from human foreskin for the purpose of foreskin reconstruction in circumcised males"; Journal of Tissue Engineering; December 2018 "Loss of the foreskin’s gliding action causes circumcised males more difficulty in penetrating their respective partners, as the force required for penetration is increased 10-fold." [citing Taves and a 2004 study about erectile dysfunction following adult circumcision]
37. Kulvinder Kochar Kaur et al; "How does HIV Gain Entry into Male Genital Tract-Utilizing knowledge from Male Medical Circumcision Trials - A Minireview"; ACTA Scientific Microbiology; February 2019. "Though foreskin is not necessary for penile functioning normally, it is believed to offer some physical and immunological protection, to the sensitive glans penis.“ [citing Taves]
38 Baky Fahmy, Mohamed Abdel A; "Normal and Abnormal Prepuce"; Springer; March 7, 2020. Taves is cited in Chapter 1 and Chapter 7: Raveenthiran Venkatachalam; "History of the Prepuce" p 20 - "In a simulated experiment Taves demonstrated that rolling back of prepuce during intercourse facilitates easy penetration of the glans."; Irene Paraboschi and Massimo Garriboli; "Functions of the Prepuce" p 71 - "In an experimental study, Taves et al. proved that an unretracted foreskin reduces the force required to penetrate by tenfold."
39. Janine Jewanra, Sinaye Ngcapu; “Semen: A modulator of female genital tract inflammation and a vector for HIV-1 transmission”; American Journal of Reproductive Immunology; June 2, 2021. ”In uncircumcised males, the foreskin provides both physical and immunological protection to the glans.” [citing Taves]
40. J.S. Svoboda et al; "Protecting All Children: Affirming the right to genital autonomy of every child"; International NGO Council on Genital Autonomy; April 2022. "The foreskin keeps the glans moist and facilitates a gliding action promoting pleasurable sexual sensations." [citing Taves and others]