The infamous "penis game."
As college students, we all experience being exposed to sexual or somewhat immature jokes regarding penises, or more specifically, penis sizes. In fact, there is a vast spectrum of different penis sizes that exist in the world. The shortest penis recorded is 1cm (0.39 in) long, whereas the longest recorded is 34cm (13.5 in) long, representing a 34-fold difference. Human species is the only organism that shows such diverse genital sizes. The size of the penis can be measured in two ways: length and width. In this blog, we will be focusing more on the length aspect than the girth, although a survey from BMC Women's Health actually did reveal that for women, sexual preference for width is a much more important factor than length for sexual stimulation.
*Fun Fact: any person who prefers to have sexual relationships with a partner who has larger-than-average penis size is called the "size queen."
Video 1. Fun YouTube video where the male is using his "magic trick" to seduce the females.
*I apologize for the Korean title! It means "how Casanova seduces girls".
*Fun Fact: in self-measurement surveys, the reported length of the penis is usually 2~3 cm longer than the actual length.
Figure 1. Map showing the average penis length. Keep in mind that these are average values!
So how do males view their penis sizes themselves? Quite surprisingly, the male self-perception of their own penis is pessimistic; they tend to underestimate their own size. There are a few theories that tries to explain this phenomenon. First, when males see their own penis, they usually are looking down, creating an optical "foreshortening." This negative self-perception also might come from media and pornographic representation, which often have actors with abnormally sized penises. Especially with the invention of clothing and the culture of covering the private parts, males rarely have encounters where they see others' genitals, thus the only image they can compare to come from these outside representations.
*Fun Fact: there are actually three different ways of measuring the penis length: flaccid, stretched, and erect. And all three of these measurements does not correlate with each other.
Figure 2. Histogram of penis length (inches) in the United States.
Why do men worry about their penis length so much? The fact that companies that market penis enlarging creams or instruments make a good fortune represents the men's desire for "more." Some men even develop impotence, or erectile dysfunction, if women make belittling comments about their dimensions. So the psychological aspect definitely kicks in. For men, the phrase "size matters" rarely leaves their minds. Most men indeed have penises that are long enough for reproductive success. The fact is that there are females and homosexual males that do believe in "bigger the better."
Video 2. Interviews of females and homosexual males regarding the importance of penis size in sexual pleasure. Keep in mind that the sample size is small and can be biased. At 0:43, she actually uses the term "size queen" as mentioned above.
*Fun Fact: Any penis shorter than 7cm is considered to have micropenis condition.
Figure 3. An example of a penis-enlarging instrument that traps blood in the penis during erection.
So we touched on the societal and intrapersonal perspectives of looking at penis sizes. Delving into the evolutionary biological aspect of the human penis: how are we doing interspecifically? Do any other animals have larger penis size than we do? The good(?) news is that human males have the largest penis out of all the great apes, despite the fact that some other apes have much bigger body sizes.
*Fun Fact: in terms of reproductive success, the human penis only has to be 7cm long for successful fertilization.
So how did we end up having the biggest penis? Evolutionary biologists are seeking to find the answer through investigating sexual selection associated with the evolution of upright posture of human species. As early hominids starting walking upright, their copulation method also became face-to-face, rather than male being on top or behind. This led to much more difficult copulation success, as well as less pleasure for the females, as their sexual organs were still oriented rearwards. One plausible hypothesis that we can come up with from this is that males with larger penises were sexually selected, for both the pleasure and the reproductive successfulness.
Figure 4. Peacock boasting its sexual healthiness to peahen. In one aspect of evolution, this can be an analogous situation as abnormal human male penis size.
This idea can be connected to one of the evolutionary terms that we learned throughout the semester: linkage disequlibrium. The two sets of genes, one for having large penis and another for preference for large penises, are selecting each other, using the penis size as the signal. However, this conjecture requires a confirmation that penis size in fact has a significant genetic component. I haven't found any scientific investigation that studied heritability of penis size in humans, although it has been done in other species, such as the ones we covered in class. The closest study I found was done by National Center for Genome Research, where they reported that body size, penis size, comes both from the father and the mother. Perhaps longer penis ensured higher rate of reproduction? I wasn't able to find any data whether penis longer than 7cm (mentioned above) has any advantage in terms of fertilization success rate.
*Fun Fact: There are other animals that enjoy sex, not just for evolutionary instinct, but for pleasure, such as gorillas, bonobos, dolphins, and chimpanzees.
Figure 5. Dolphin copulation. Let's give them some privacy..
*Fun Fact: animal that has the longest copulation duration is rattle snake- they can last for more than 22 hours!
To sum up, the topic of penis size is and will remain an interesting evolutionary and social issue and phenomenon. After the emergence of sexual reproduction and copulation, the sexual organs have gone through biological evolution according to the demands and selection. Socially, evolutionarily, sexually, aesthetically, psychologically, and biologically, penis length are going through, and will go through variation again, and it would be interesting to continue this investigation. In the end, human species do not mate choose mates solely by the penis size.
*Last Fun Fact: animal with the overall longest penis is the Argentine Blue Bill Duck, with 42.5cm (17 in) long penis. I didn't include the picture, but if you want to see it, here's the link.
Any comments or questions welcomed!
PS. I think I posted about 5 articles on penises. I promise this will be the last one!
Eisenman, R (2001), "Penis size: Survey of female perceptions of sexual satisfaction." BMC Women's Health: 1. doi:10.1186/1472-6874-1-1.
Wessells, H.; Lue, T.F.; McAninch, J.W. (1996). "Penile length in the flaccid and erect states: guidelines for penile augmentation". The Journal of Urology 156 (3): 995-997. doi:10.1016/S0022-5347(01)65682-9.
"Length-boosting surgery for 'micro-penises'". New Scientist. 2004-12-06.
Pertschuk, Michael; Trisdorfer, Alice. "Men's bodies- the survey". Psychology Today. Retrieved 2007-07-17.
Jahme, Carole. "Penis size: An evolutionary perspective." Guardian UK. May 6th, 2010.
Seduction Labs. "Human penis size and evolution." Jun 5th, 2007 <http://www.seductionlabs.org/2007/06/05/human-penis-size-evolution/>
AskWhy! "Evolution of Human Penis." <http://askwhy.co.uk/dinosauroids/?p=315>
"Why Evolution Is True." March 21st, 2011 <http://whyevolutionistrue.wordpress.com/2011/03/21/geographic-variation-in-human-penis-size/>