Picture this: you’re the parent of a sporting prodigy, a teenage girl who seems destined for global success. Her whole life, she has worked with obsessive dedication, placing sport above academic or professional pursuits to chase her ultimate dream: Olympic gold.

When she gets there, she lines up beside a cluster of athletes with differences of sexual development (DSD), who, in a strictly biological sense, are part-male. Some were born with internal testes which, when they hit puberty, flooded their system with testosterone, giving a boost in muscular development that is unavailable to more than 99% of their female peers.

The only athletes to run faster than these women are widely accepted to be dopers, meaning your daughter’s only hope of winning is to artificially boost her testosterone levels with anabolic steroids. Otherwise, she can train as hard as she wants, but she’ll never win. It won’t even be close.

Is that fair?

And what if this wasn’t a race, but a boxing match? Would that change how you feel?

Now picture this: you’re the parent of three daughters. From birth you’re made aware the biology of your youngest doesn’t neatly fit into the male or female archetype, but lies somewhere in between. But to you, to her, she will only ever be a girl.

In her teens she develops muscle in different ways to her sisters, and soon discovers a love for sport. She keeps getting better, keeps working harder, until she eventually qualifies for the Olympics, at which point she is asked to undergo a medical examination.

Doctors discover her testosterone levels are through the roof and that she has internal testes, and tell her that to compete as a woman she must take medication that will lower her testosterone levels closer to the female range or else undergo surgery to achieve the same outcome. Otherwise, she can compete against men, or stay home.

Is that fair?

Therein lies the nub of the debate about Caster Semenya’s challenge to the IAAF’s testosterone rules, set to be decided in the coming month at the Court of Arbitration for Sport (CAS). Both parents would believe their daughter is not being given a fair chance. And both may be right.

But for all the talk about Semenya, who has been unbeatable at 800m since 2015, this is ultimately not about her. Her case will establish a ruling with long-lasting repercussions across sport, and not just for DSD women. The International Olympic Committee is reportedly awaiting the decision to decide its regulations for transgender athletes ahead of the 2020 Games.

DSD and transgender athletes are different, of course, but sport may ultimately have to treat them the same. Both are unquestionably women, but both may also have a performance edge due to male sex organs.

Many intelligent, informed and well-meaning experts have argued that all women, regardless of biology, should be free to compete unrestricted. If that includes women who were until recently men, so be it. If it includes women with internal testes which produce testosterone in the male range? Well, biology isn’t fair, they argue, citing the wingspan of Michael Phelps or the stride length of Usain Bolt.

But here’s the thing: if we are to accept the unregulated presence of male biology in women’s sport, that women born without male sex organs must compete against those who have them on the premise that biology is fundamentally unfair, why not abandon the women’s category altogether?

After all men and women compete against each other in horse racing – why not in athletics, or boxing? The answer is obvious, and should underpin the debate about women’s sport which is, fundamentally, a protected category.

And it’s one we must protect.

But what is a woman? And should the dividing line be different in sport than society? That’s the key question, one no one can fully answer.

Many critics of the regulations have called them racist, which ignores the fact that in Semenya’s event, 13 of the 14 best athletes in the world last year were black. If DSD athletes are slowed by these regulations, the athletes who will soon fill the podium – who will benefit most – are black women.

No one doubts the deeply upsetting situation Semenya has had to deal with enduring, invasive examinations and crass, insensitive commentary, but it’s possible to sympathise with her while also sympathising with her rivals, who are in a race they cannot win – at least without doping.

In recent weeks I spoke to an agent of a world-class 800m athlete, who explained the desperation felt by women who run against DSD athletes.

They are broken,” he said. “When they walk off the track, more than anything they want to scream.

When interviewed, though, such athletes will rarely offer an honest opinion, aware that remarks about unfair advantages will likely label them a jealous, potentially even racist, sore loser.

Truth is, the majority in athletics have both great sympathy and immense respect for Semenya, whose charisma is renowned, but the majority also believe women’s sport should not be an open door for those with either partial or fully male biology, at least without testosterone regulation.

In many ways, this debate offers a depressing window into wider society, where differing views are shouted down with vicious intolerance by those who’d deem themselves progressive. People should be free to argue that women with internal testes have a right to compete for top prizes without being ridiculed, just as they should be free to argue it’s unfair without being labelled racist or transphobic.

But worst of all are those hijacking this issue for commercial gain. In an ever-more desperate bid to masquerade salesmanship as social justice, Nike launched an ad last week featuring Semenya running to a voiceover from Serena Williams, who says with a not-so-subtle dig:

When we’re too good, there’s something wrong with us.

This is Nike, climbing aboard an ethical plinth for women’s rights – a company facing a lawsuit by four former female employees for alleged violations of US equal-pay laws and for fostering a work environment that allowed sexual harassment. Nike, flying its flag for equality, a concept workers at factories in Honduras and Vietnam must find deeply ironic.

But the biggest problem in all of this? There is simply no right answer, no solution to satisfy all parties.

The best one, I believe, is that currently being offered to DSD athletes – that if they choose to enter the elite echelon of women’s sport and compete for huge rewards with biology that is partially male, they should lower their testosterone levels closer to the female range.

But having said that, I still expect Semenya to win her case, that the regulations will be suspended.

If so, it will mean DSD athletes continue to prosper in elite athletics. Great news for them, but not so great for their rivals who were born without such complex – but in a sporting sense, ultimately beneficial – biology.

Critics have slammed the regulations, often with good cause, but they grow quieter when asked how best to draw a dividing line between genders, or to acknowledge that the presence of male biology can offer a sizeable advantage in women’s sport.

And that’s the problem. Two warring factions, and both parents may be right. But which daughter deserves to win?

What will the DSD ruling mean?

The International Association of Athletics Federations has delayed the introduction of a testosterone limit for female athletes until after a verdict is reached on Semenya’s appeal to CAS against the rule.

In a statement explaining its position, the IAAF said: “If a DSD athlete (with differences in sexual development) has testes and male levels of testosterone, they get the same increases in bone and muscle size and strength and increases in haemoglobin that a male gets when they go through puberty, which is what gives men such a performance advantage over women.

Therefore, to preserve fair competition in the female category, it is necessary to require DSD athletes to reduce their testosterone down to female levels before they compete at international level.

The new limit, which only applies to races from 400m to one mile, was meant to come into force on November 1, and would require athletes to maintain their testosterone levels to below five nanomoles per litre (nmol/L) for at least six months before competing.

For affected athletes, this would mean taking hormone suppression tablets, similar to oral contraceptives.

Semenya’s victory at the 2009 World Championships in Berlin — her first of three world and two Olympic 800m titles — began an often shameful public debate about the then 18-year-old’s gender.

It brought about IAAF’s first attempt to set a limit for testosterone and its hyperandrogenism rule was in place until Indian sprinter Dutee Chand challenged the rule at the CAS in 2015.

The Swiss-based court ruled there was a lack of evidence to support the rule and suspended it for two years, pending further research.

Having asked for six more months to complete that research, the IAAF came back to CAS earlier this year with what it claimed was statistical proof that high levels of testosterone do provide an advantage and it is particularly significant on the track between 400 metres and one mile. This evidence has not been universally accepted by sports scientists, while other critics of the policy have also questioned its fairness.

Semenya has said: “I just want to run naturally, the way I was born. It is not fair that I am told I must change. It is not fair that people question who I am.”