It's one of the most contentious questions in the evolution of human sexuality: why does the female orgasm exist? Historically ignored and disparaged by scientists, the role of the clitoris in sexual arousal remains cloaked in enigma, even to this day.

Unlike men, whose sperm is crucial for reproduction, women do not need to orgasm in order to have children, and in the vast majority of cases, normal intercourse does not stimulate their clitoris enough to reach a climax.

So why does it even exist? Today, there are two broad and competing theories, both of which have their limitations.

Depending on which you believe, the female orgasm either evolved to help select the best mate, or it's a mere byproduct of the male orgasm - a remnant of our ancient past that no longer serves any evolutionary function, kind of like nipples on men.

But maybe, just maybe there's another explanation we've been overlooking. Biomedical scientist Roy Levin from the UK has now written a contentious new review proposing a fresh, updated role for the clitoris.

"Despite numerous modern accounts that characterise the activation of human female sexual arousal by clitoral stimulation none appear to have referred to it possessing any involvement in a specific reproductive role," he writes.

"Nearly all repeat the mantra that 'the clitoris is the only human organ whose sole function (my italics) is the transmission of sexual pleasure'."

Levin thinks this is a huge oversight. Analysing recent research, he instead argues that the clitoris exists equally for both enjoyment and reproduction. It's a major challenge to current theories and beliefs, but Levin thinks it's about time we re-examined the evidence.

When the clitoris was first mentioned in the 1500s, it was mistakenly thought to have a role in the urinary tract, and some physicians argued it didn't exist in healthy women at all.

Nowadays, we know a whole lot more about this part of female anatomy, but our overwhelming fixation on its role in sexual pleasure may have masked a more subtle function: it's ability to transport and retain male sperm.

Before the highly sensitive clitoris reaches a zenith of sexual pleasure, recent studies have shown it causes activation in all major brain systems, including areas involved in arousal, reward, memory, cognition, and social behaviour.

This widespread brain activity then leads to genital changes, like increased blood and oxygen flow, as well as warmth and lubrication. When nearing an orgasm, the outside of the vagina can also form an 'orgasmic platform', lifting the uterus to accommodate sperm, and during an orgasm, the pelvic floor muscles rhythmically contract.

Not only does this induce sexual arousal, Levin explains, it prepares the female body for reproduction, ensuring the greatest potential for fertilisation. For instance, the changes to the shape of the cervix stops semen from travelling into the uterus too quickly, allowing the sperm time to grow stronger and more mobile.

"The often repeated mantra, that the sole function of clitoris is to induce sexual pleasure, is now obsolete," says Levin.

"The concept changes a major sexual belief, and the physiological evidence is now obvious."

But while the idea might appear self-evident to Levin, it's doubtful everyone will be so easily convinced. While detailed reviews have also proposed a sperm-selection role behind the female orgasm, the physiology of this mechanism is still under dispute and additional research will probably be needed before we can draw any strong conclusions.

Some studies show that following the release of oxytocin (a hormone associated with sexual arousal), fluid is sucked into the fallopian tube, and when this type of pressure change exists, pregnancy rates are significantly higher.

Plus, fertility research in other non-human species, like rats, cows, dogs, horses and rabbits, suggests similar transport and retention of sperm. Among cats, rabbits and ferrets, for instance, the clitoris is located inside the vagina, and at least for these animals, research suggests the female orgasm is essential to procreation.

A study in 2019 found that female rabbits who did not orgasm ovulated 30 percent less, and this suggests that in our own distant evolutionary past, the female orgasm might have stimulated egg release, helping us create new offspring.

Nowadays, however, with the human clitoris having migrated to a new location, such benefits could have disappeared, leaving only the orgasm behind.

"If this theory is correct," says evolutionary biologist Gunter Wagner, "none of those older ideas are valid."

Levin, on the other hand, thinks this theory misses the main sequence of events.

"What they obviously overlooked in formulating their hypothesis is that clitoral stimulation activates, via the brain, a series of physiological changes that precede the induction of orgasm/ovulation," he writes, "and that these changes prepare the human female genital tract for the possible entry of semen."

In other words, just because the clitoris has moved, doesn't mean it no longer plays a role in fertility. Today, the widespread brain activity seen in humans post-orgasm and the physical changes that causes, appear to make it easier for sperm to survive, with little effect on ovulation.

It's a super tricky, complicated subject, made all the more difficult by historical negligence.

As much as we've learned, the mystery behind the female orgasm will no doubt continue for many more years. But if we continue to think of the clitoris only in terms of pleasure, we might not find the answers we are looking for.

The study was published in Clinical Anatomy.