Circumcision has been shown to reduce the risk of contracting a number of STDs [1,2,16]. Studies now provide evidence that that humans are in fact evolving out of foreskin [3,4]. The first study measured the foreskin length of a large cohort of uncircumcised Chinese men using the following classification.
The study found that the general Chinese male population (‘the control group’) fell into the following classifications.
As is shown, 22.9% of men in the general population, (‘control group’) have level 1 foreskin length, which is naturally circumcised (the foreskin is shortened to the point where all of the glands of the penis are exposed). Another 18.2% of the population has their foreskin cover less than half of the glands of their penis, which is quit close to being naturally circumcised. All together around 40% of Chinese men are more or less naturally circumcised. This study as well as others [3,4] also find that men that test positive for STD’s have longer foreskin on average, and the difference grows greater when accounting for frequency of sex and for age. All together these studies show that, especially in the Chinese population and mostly likely some other East Asian ethnicities, natural selection favors men with shortened foreskin.
Why Have Humans Just Started Evolving Out of Foreskin?
Foreskin is apart of our phylogenic heritage, all of the great Apes have it and we inherited the trait from our ancestors. Infectious diseases (including STDS) where thought to not have been an issue for humans until around 10,000 years ago when the agricultural revolution took place and humans began forming large communities where diseases could easily spread amongst a large population.[18,19] Prior to this time humans lives in very small tribes and rarely made contract with other groups of humans, thus greatly reducing the spread of diseases. Even after this time many humans still lived very small dispersed groups and not in large communities. It is thought agriculture did not reach Western Europe until just 4,000 years ago and many serious STDs like syphilis did not reach this population until just a few hundred years ago (syphilis was though to have come to Europe from their contact with North America). Before humans began to live in communities there would have been little benefit for a man to have resistances to STDs since only a couple of STDs (or even none) may have existed in a given population and at a low prevalence. Thus even if having foreskin provided just the smallest of benefits or even none at all, humans and our relatives would have kept it.
how can circumcision have both health benefits and lack consequences?
Circumcision has been associated with a number of health benefits including a reduced risk of urinary tract infections, penile and prostate cancer, and STD infection [1,2, 16]. Now the question of why do men have foreskin if circumcision is beneficial arises. As mentioned before in this article, a lack of foreskin being beneficial has only arisen recently in history with the rise of infectious diseases and humans have not had enough time to fully evolve out of it. Some people argue that foreskin plays a role in sexual pleasure, but a number of studies following men’s experience with adult circumcision indicate that very few men report a decrease in sexual function or pleasure, with the large majority of men rating their sex life as the same or even better after undergoing circumcision regardless if they are asked a few months or a few years after getting circumcised (these studies are talked about in the next section of this article).
At the heart of this discussion are two arguments. The first argument is that most of the health benefits that are gained from circumcision only become noticeable at a point in life where the large majority of men would not be likely to father any more children, thus from the viewpoint of natural selection there is only a small difference in a man being circumcised (or having reduced foreskin) or uncircumcised (natural selection only cares about what genes help you have the most amount of kids. So if certain genes can improve your health past a point where you have had your kids natural selection won’t view them as beneficial since it hasn’t helped you have more kids). For something like penile or prostate cancer this is clear, most cases happen after the age of 60 and rarely occur before the age of 40, but in a more subtle way this is also true for something that confers a resistance to STDs only for men. To begin with, STDs can only begin to affect a man after he has started reproducing and passing on his genes, in addition most young men who have had few to no sexual partners tend to have relations with women who have had few to no sexual partners and so these women are at a lower risk of having an STD, and so the men are less likely to contract an STD from them. This would imply that most men contract an STD when they are older and have already had a few children, and current statistics from the age of HIV diagnosis back up this theoretical reasoning; nearly twice as many men contracted heterosexual HIV between the age of 34-39 (356 new cases in 2015) in the USA then men between the age of 20-24 (194 new cases in 2015). The most serious STDs like HIV, high risk HPV, and Syphilis typically take 5 years to as man as 30 years to bring about serious consequences, and during this latency period men may continue to pass on their genes relatively uninhibited. In general, since STDs are transmitted through sex, STDs must give a man some time period where it does not greatly affect an infected man’s sex life so he might be able to pass on the disease. At the same time though, he is able to continue reproduction and pass on his genes relatively unaffected. As in all mammals, the females are the primary caregivers for young children, so the absence of the child’s father would mostly likely not greatly effect the child, and as mentioned before STDs typically take 5-30 years before serious consequences arise from them at which point most of the fathers children would be at a point where they would be mostly independent. The second argument in this discussion is that in spite of the fact that natural selection would only view the benefits of circumcision or reduced foreskin as being very small, there appears to be at least some ethnicities where natural selection has favored the loss of foreskin. Since natural selection has favored shortened foreskin and natural selection only views the benefits of circumcision as small, it must view the benefits of foreskin as even smaller, if there are even benefits at all.
Studies conclusively show circumcision does not harm sexual pleasure or function
A significant number of studies have shown that foreskin does not play a role in sexual pleasure, including the 2007 World Health Organization and UNAIDS own findings on circumcisions effect on sexual pleasure, stating “Although it has been argued that sexual function may diminish following circumcision due to the removal of the nerve endings and subsequent thickening of the epithelium of the glans, there is little evidence of this”, the 2012 American Academy of Pediatrics own findings on circumcisions effect on sexual pleasure, stating “The literature review does not support the belief that male circumcision adversely affects penile sexual function or sensitivity, or sexual satisfaction, regardless of how these factors are defined”, a 2016 systematic review conducted by Danish researchers that found grade A evidence that circumcision in fact increases penile sensitivity and rejected the hypothesis that circumcised men experience inferior sexual function , a 2013 systematic review conducted by Australian researchers which found that studies that were rated as high quality from the Scottish Intercollegiate Guidelines Network gave indicate circumcision does not negatively impact sexual function, sexual sensitivity, sexual sensation or sexual satisfaction , and a 2013 meta-analysis and systematic review conducted by Chinese researchers which found circumcision in unlikely to have an adverse effect on sexual function , the Center of Disease Control 2014 guidelines on circumcision which states that few men report a decrease in sexual pleasure, more men report an increase, and almost all report either an increase or no change in sexual pleasure after undergoing circumcision , and numerous individual studies [10-15].
 World Health Organization and UNIADS: New Data on Male Circumcision and HIV Prevention: Policy and Programme Implications http://apps.who.int/iris/bitstream/10665/43751/1/9789241595988_eng.pdf http://www.who.int/hiv/pub/malecircumcision/research_implications/en/
 The American Academy of Pediatrics 2012 evaluation of circumcision:
 Redundant Prepuce Increases the Odds of Chronic Prostate/Chronic Pelvic Pain Syndrome. Zhao et al. (the table with foreskin lengths is the 4th image and 3rd table given in the paper. it is labeled ‘OR for CP/CPPS with respect to foreskin length’. The general Chinese population is the control group.) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4215657/
 Acceptability of Voluntary Medical Male Circumcision Among Male Sexual Transmitted Disease Patients in China. Wang et al. (foreskin lengths were measured by doctor and are given in the first table of the paper) https://www.ncbi.nlm.nih.gov/pubmed/26905739
 2007 World Health Organization and UNIADS: Male Circumcision, Global Trends and Determinates of Prevalence, Safety, and Acceptability http://www.unaids.org/sites/default/files/media_asset/jc1360_male_circumcision_en_0.pdf
 Male Circumcision Does Not Result in Perceived Male Sexual Function – A Systematic Review. Shabanzadeh et al http://www.danmedj.dk/portal/page/portal/danmedj.dk/dmj_forside/PAST_ISSUE/2016/DMJ_2016_07/A5245
 Effects of Male Circumcision on Male Sexual Functions: A Systematic Review and Meta-Analysis. Tian et al https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3881635/?report=reader
 Does Male Circumcision Affect Sexual Function, Sensitivity, or Satisfaction? A Systematic Review http://www.jsm.jsexmed.org/article/S1743-6095(15)30172-7/abstract
 Adult Male Circumcision Performed with Plastic Clamp Technique in Turkey. Results and Long-Term Effects on Sexual Function. Senel et al. http://www.urologyjournal.org/index.php/uj/article/view/1802/693
 Longer-Term Follow-Up of Kenyan Men Circumcised Using the ShangRing Device. Feldblum et al. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4569077/?report=reader
 Does Circumcision Affect Male’s Perception of Sexual Satisfaction? Cortes-Gonzales et al. https://www.ncbi.nlm.nih.gov/pubmed/19955598
 Effects of Adult Male Circumcision on Premature Ejaculation: Results from a Prospective Study in China. Gao et al. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4324807/
 Adult Male Circumcision: Effects on Sexual Function and Sexual Satisfaction in Kisumu, Kenya. Krieger et al. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3042320/?log$=activity
 Effects of Circumcision on Male Sexual Function: Debunking a Myth? Collins et al. https://www.ncbi.nlm.nih.gov/pubmed/11956452
 CDC: Male Circumcision https://www.cdc.gov/hiv/pdf/prevention_research_malecircumcision.pdf
 CDC HIV Surveillance Report 2015 (page 33 contains date on age of HIV diagnosis for all races) https://www.cdc.gov/hiv/pdf/library/reports/surveillance/cdc-hiv-surveillance-report-2015-vol-27.pdf
 Early Concepts of Diseases: Boston University http://sphweb.bumc.bu.edu/otlt/mph-modules/ep/ep713_history/ep713_history2.html
 Long Run Health Effects of the Neolithic Revolution http://paa2013.princeton.edu/papers/132307