LIKE most body parts, penises come in all shapes and sizes.
But one thing most have in common is the mushroom-shaped tip.
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Unsurprisingly, people are fascinated by why it looks this way – and it turns out, there are several theories.
Scientists from the State University of New York put one of them to the test in 2003, with compelling results.
Why is the penis mushroom-shaped?
Some experts believe the penis is shaped the way it is due to the “semen displacement theory”.
This is quite simple – in order for men to ensure they carry on their lineage and impregnate a woman, their penis acts as a “tool”.
It has a ridge to scoop out the semen of love rivals from the vagina, or so the idea says.
As the semen from another male is removed, it is replaced with that of the new partner, increasing the chances of him becoming a father if the woman has had sex with multiple people in a short amount of time.
Nowadays, having a mushroom-shaped penis doesn’t seem entirely necessary.
But from a natural-science perspective, it makes sense, as humans biologically want offspring.
The ‘scooping out’ mechanism would have been much more useful hundreds of thousands of years ago when humans were considerably more occupied with procreating.
Put to the test
A team at State University of New York, led by Professor Gordon Gallup, looked into this theory and published their findings in the Journal of Evolutionary Psychology.
They found the thrust of the penis – and the ridge that separates the head from the shaft – could indeed help clear a woman’s vagina and reproductive system of a previous lover’s sperm.
They tested their theory in the lab, with latex penises and model vaginas.
Mixing starch and water together to make a solution similar in consistency to semen, they found the ridge around the top of a man’s penis could scoop out around 90 per cent of the “semen” substitute in just one thrust.
But a fake penis without a ridge only managed to remove about 35 per cent of the “semen”.
Depth of thrusting was also important for clearing the vagina.
Professor Gallup said: “We theorise that as a consequence of competition for paternity, human males evolved uniquely configured penises that function to displace semen from the vagina left by other males.
“Thus, the human penis may enable males to substitute their semen for the semen of their competitors.”
With surveys, the scientists found evidence that couples tend to have more energetic sex if the woman has been suspected of cheating, or if a couple has been apart.
It could, he said, be because the male has a subconscious desire to rid his partner of any trace of another man’s semen.
Professor Gallup’s colleague Rebecca Burch added: “A longer penis would not only have been an advantage for leaving semen in a less accessible part of the vagina, but by filling and expanding the vagina it also would aid and abet the displacement of semen left by other males as a means of maximising the likelihood of paternity.”
Other theories
Some believe that the penis may simply have its shape in order to make sex more pleasurable for both men and women.
And the penis may look more desirable in its current form, rather than a simple lengthy shape.
Others reckon it’s down to hormones like testosterone and dihydrotestosterone.
What other penis shapes are there?
Theories aside, there are many different kinds of penis shapes, from the pencil, to the sausage and cone shape.
There is no standard shape, and no penis should be considered normal or abnormal.
Size, girth, angle or circumcision are all among the factors that can lead men to have different-looking penises – all of which do the same job.