While “size matters” might seem like a sensational headline, for evolutionary biologists, the dimensions of the human penis present a genuine scientific conundrum.
In comparison to other prime ape species, such as chimpanzees and gorillas, the human phallus is disproportionately longer and more robust than would be anticipated for a primate of our bodily scale.
If the sole functional imperative of a penis is the conveyance of gametes, then the considerable disparity in size compared to our closest evolutionary kin warrants investigation.
Our recent investigation, disseminated today within the pages of PLOS Biology, posits that a larger human penis fulfills a dual role beyond mere reproductive function: it serves to enhance mate attraction and to intimidate rivals.
Investigating the Prominence
The inquiry into the origins of distinctive human physical characteristics is a prominent area within evolutionary science. It is already established that certain morphological attributes, such as increased stature and a more inverted triangular torso, contribute to heightened male sexual appeal.
However, the impact of a larger penis on perceived attractiveness remains less understood. Humanity’s bipedal locomotion predates the widespread adoption of clothing, rendering the penis a conspicuous feature to potential mates and competitors throughout the majority of our evolutionary history.
Could this visibility have exerted selective pressure favoring augmented dimensions?
A decade prior, in a seminal study, we presented female participants with life-sized digital renderings of 343 anatomically accurate, 3D computer-generated male figures. These figures were designed to exhibit variations in height, shoulder-to-hip ratio, and penile dimensions.
Our findings demonstrated a discernible preference among women for individuals possessing greater height, broader shoulders, and a larger penis.
While this research garnered significant international attention, it represented only a partial explanation. Our current study elucidates that male perception of penis size is also a relevant factor.
A Bifunctional Hypothesis?
Across numerous species, traits that are particularly pronounced in males, such as the mane of a lion or the antlers of a deer, typically serve a dual purpose: they are aesthetically appealing to females and they serve as indicators of competitive prowess to other males. To date, it remained unconfirmed whether human penis size might operate under a similar bifunctional model.
Our new research re-affirmed the prior observation that a larger penis is perceived as more attractive by women. Subsequently, we investigated whether men also perceive a rival with a larger penis as more appealing to women, and crucially, we sought to determine if men interpret a larger penis as a signifier of a more formidable adversary in hypothetical confrontations.
To obtain these insights, over 800 individuals were exposed to the 343 digitally rendered figures, which varied in height, body morphology, and penile size. Participants engaged with and evaluated a selection of these figures, either directly through life-sized projections or remotely via online platforms on their personal devices.
Female participants were tasked with rating the figures based on their sexual desirability. Concurrently, male participants assessed the figures as potential rivals, evaluating their perceived physical threat and competitive efficacy in a romantic context.
Key Findings
For women, enhanced penile size, greater height, and a V-shaped upper torso all contributed to increased male attractiveness. However, a point of diminishing returns was observed: beyond a certain threshold, further increases in penile or stature dimensions yielded progressively smaller gains in desirability.
The most significant revelation, however, emerged from the male participants’ evaluations. Men interpreted a larger penis as indicative of a rival possessing superior combat capabilities and a more potent capacity for sexual competition. Similarly, taller individuals with a more pronounced V-shaped physique were assessed by men in a comparable manner.
Intriguingly, unlike the female respondents, men consistently assigned higher scores to figures exhibiting increasingly exaggerated traits as stronger sexual competitors. This suggests a tendency for men to overestimate the appeal of these characteristics to women.
The uniformity of our findings was particularly noteworthy. The assessments of the various figures yielded remarkably congruent conclusions, irrespective of whether participants observed the stimuli as life-sized projections in situ or viewed them on smaller digital displays online.
Immediate Impressions – With Caveats
It is imperative to acknowledge that the primary evolutionary driver for the human penis was undoubtedly sperm transfer. Nevertheless, our research provides evidence that it also functions as a biological signaling mechanism.
We now possess empirical support suggesting that the evolution of penile size may have been influenced, in part, by female mate selection preferences and its role as a signal of physical prowess among conspecific males.
It is important to note, however, that the impact of penis size on perceived attractiveness was found to be four to seven times greater than its effect as a signal of combative ability. This ratio implies that the augmented size of the human penis evolved predominantly as a sexually selected ornament to attract females, rather than solely as a marker of male dominance, although it appears to serve both functions.
Furthermore, our study highlighted an interesting psychological phenomenon. We quantified the speed at which participants rendered their judgments. Individuals exhibited significantly faster reaction times when evaluating figures characterized by a smaller penis, reduced height, and a less V-shaped upper body. This expedited response suggests that these specific attributes are, on a subconscious level, almost instantaneously categorized as less sexually appealing or physically threatening.
Naturally, the scope of what our experimental design can reveal is subject to certain limitations. While we systematically manipulated male height, penile dimensions, and body shape, real-world assessments are also influenced by other crucial factors such as facial morphology and personality traits. Further investigation is required to ascertain the interplay of these elements.
Moreover, while our findings demonstrated robustness across diverse ethnicities and genders, it is acknowledged that perceptions of masculinity are subject to considerable cultural variation and temporal shifts globally.
