In the human lineage, sensory penile spines were lost. A 2011 genomic study by McLean and colleagues found that a deletion of a conserved regulatory sequence, an enhancer, near the androgen receptor gene correlates with that anatomical loss, and confirmed 510 complete deletions of otherwise highly conserved sequences in humans, most of them non-coding. Whether the loss changed how men experience sex is a hypothesis, not a demonstrated effect. Multiple orgasm in men is a separate and uncommon phenomenon, with no established relation to penile spines.
The distinction matters because a genomic correlation is often reported as a behavioural cause, and that step is not supported by the data.
What do we know about the loss of penile spines in humans?
What is established is a correlation between a genomic deletion and an anatomical loss. McLean and colleagues, 2011, confirmed 510 complete deletions of otherwise highly conserved sequences in humans, almost all in non-coding regions. A deletion removes a sensory vibrissae and penile spine enhancer from the androgen receptor gene, a change correlated with the anatomical loss of penile spines.
A genetic correlation is not an effect on sexual behaviour. — Image: AI-generated / Gemini 3.1 Flash via OpenRouter
The deletions are not scattered at random. They are enriched near genes involved in steroid hormone signalling and neural function. A deletion near the GADD45G gene is correlated with expansion of specific brain regions.
The paper did not test effects on sexual behaviour and made no claim about what the loss does for behaviour. A deleted sequence is a difference between genomes, and a difference is not an effect on human sexual behaviour.
Why is the penis so diverse across species?
Hosken and colleagues, 2019, describe the penis as an incredibly diverse and rapidly evolving structure. Even closely related species that otherwise differ little in morphology can differ strongly in penis form, and penises are more complex than their basic function of sperm transfer requires. Rapid divergent evolution is typically the signature of traits under sexual selection.
Current evidence suggests the penis is no different, and the general agreement is that sexual selection is the main driver. Beyond that, many questions about penis evolution remain unresolved.
Is the loss of spines linked to human sexual behaviour?
No causal link has been established. The 2011 genomic study reported a correlation with anatomical loss and did not test behaviour. The proposal that the loss altered human sexual behaviour is a hypothesis that remains unproven.
[More research needed: none of the sources reviewed for this article tested the effect of losing penile spines on human sexual behaviour or sexual experience.] That gap defines the state of the evidence. Genomic data describe which sequences were deleted and where they sit; anatomical data describe a structure that humans lack. Neither describes what men feel, want or do.
A behavioural claim would require behavioural data from men. Until such data exist, the accurate statement is narrow: the 2011 deletion near the androgen receptor gene is documented, and its consequence for human sexual behaviour is not.
What does science know about multiple orgasms in men?
It is uncommon, and the physiology is poorly documented. A 2016 review by Wibowo and Wassersug found that fewer than 10% of men in their 20s and fewer than 7% after age 30 report multiple orgasms, based on 15 relevant publications. Confirmatory physiological data are few.
The review distinguishes sporadic multiple orgasms, with intervals of several minutes, from condensed multiple orgasms, in bursts of 2 to 4 orgasms within a few seconds to 2 minutes. The role of ejaculation and of physiological change during the refractory period in inhibiting multiple orgasms has barely been investigated.
A 2021 survey by Griffin-Mathieu and colleagues in the Journal of Sexual Medicine collected reports from 122 men, with orgasm counts from 2 to 30; the majority, 79.5% or 97 men, reported 2 to 4 orgasms separated by an interval in which further stimulation was needed. Most kept their erections and ejaculated with every orgasm, age was not a significant correlate, and it occurred more often in a partnered context. The study had no validated measures, no control group, no physiological measurement and relied on memory. In clinical work, men who ask about multiple orgasms mostly want to know whether they are normal; the scientific answer is that both single-orgasm and multiple-orgasm experiences fall within the range of men’s experience, and the question alone is not a sign of a disorder. The popular claim that all men can have successive orgasms without rest does not match the reported figures: fewer than 10% of men in their 20s and fewer than 7% after age 30.
The 2011 genomic study indicates that the human lineage lost them. The 2011 study found that a deletion removes a sensory vibrissae and penile spine enhancer from the human androgen receptor gene, a change correlated with the anatomical loss of penile spines.
Did losing the spines change human sex?
That has not been tested. The 2011 paper did not examine sexual behaviour, and none of the sources reviewed for this article measured an effect of the loss on human sexual behaviour or sexual experience. The idea that the loss changed human sexuality is a hypothesis.
What percentage of men have multiple orgasms?
Fewer than 10% of men in their 20s and fewer than 7% after age 30, according to a 2016 review of 15 relevant publications by Wibowo and Wassersug. It is uncommon rather than typical, and confirmatory physiological data remain few.
Does not knowing this matter, or relate to sexual problems today?
The evolutionary question is separate from clinical care. Not knowing why a structure was lost does not explain an individual’s difficulties, and none of the sources reviewed here connect that loss to sexual problems. Multiple orgasms appear to be a variation in experience rather than a disorder.
A Genetic Footprint and an Open Question
The evidence leaves a genetic footprint and an open behavioural question. Our editorial position is that the story of how our bodies evolved is fascinating but must be told with exactly the precision the evidence allows; a genetic correlation cannot be turned into an explanation of sexual behaviour today. Comparative work on penis diversity continues, and better genomic and behavioural data can narrow the gap between what was deleted and what it means.
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McLean CY, Reno PL, Pollen AA, Bassan AI, Capellini TD, Guenther C, et al. Human-specific loss of regulatory DNA and the evolution of human-specific traits. Nature. 2011;471(7337):216-219. PMID: 21390129. DOI: 10.1038/nature09774
Hosken DJ, Archer CR, House CM, Wedell N. Penis evolution across species: divergence and diversity. Nat Rev Urol. 2019;16(2):98-106. PMID: 30397329. DOI: 10.1038/s41585-018-0112-z
Wibowo E, Wassersug RJ. Multiple Orgasms in Men-What We Know So Far. Sex Med Rev. 2016;4(2):136-148. PMID: 27872023. DOI: 10.1016/j.sxmr.2015.12.004
Griffin-Mathieu G, Berry M, Shtarkshall RA, Amsel R, Binik YM, Gérard M. Exploring Male Multiple Orgasm in a Large Online Sample: Refining Our Understanding. J Sex Med. 2021;18(9):1652-1661. PMID: 34404626. DOI: 10.1016/j.jsxm.2021.06.017
Image credits: featured image: Photo: Edgar Santana / Pexels (Pexels). The first inline image was AI-generated (Gemini 3.1 Flash via OpenRouter).
