Sports must consider both safety and fairness when deciding whether transgender athletes should compete against women, according to a World Rugby sports scientist.
Ross Tucker was speaking after the IRFU denied claims it advised a Northern Irish women's rugby team to pull out of an amateur tournament because the opposition included a transgender player.
The actions of Lurgan Rugby were described as "transphobic" in a full-page report in a German newspaper, which outlined complaints from the Berlin Bruisers – a team for LGBTQ+ players.
The inclusion of trans women athletes in sports has become a contentious topic, with some arguing it may give players a natural advantage.
On The Pat Kenny Show, Dr Tucker, who has a PhD in exercise physiology and is currently working as a research scientist for World Rugby, said "all sports" have to face up to the issue.
"The reality is women's sports exist for a number of reasons," he said. "One of the most important ones is because it has to exclude male biology.
"When sports fail to recognise that, you're going to create controversies like you are experiencing right now."
Safety vs fairness
Dr Tucker said the issue of "fairness" arises in both contact and non-contact sports.
"For instance, in swimming, there may not be a safety issue in the way that there is for rugby," he said.
"In combat sports, like boxing and martial arts, the safety issue would be even greater to consider.
"Whether you frame it as a safety issue for women who have to then compete against [transgender women] - where physical contact and combat are a factor - that's obviously crucial – but the fairness issue exists regardless.
"So, the track and field athlete, a swimmer, cyclist, male biology creates performance advantages – they happen to bring with them safety considerations as well.
"The fundamental issue is male biology needs to be excluded from women's sports and that's for safety and fairness reasons."
Dr Tucker said when scientists have made comparisons between the average physique of athletes, they have found "enormous" differences in their performance abilities.
"The power differences are 30% to 40%, strength differences are 30% to 50%, and speed is 15% to 20% in males compared to females," he said.
"Yes, you could find exceptional females who look better athletically than relatively mediocre males but that's not what sport is.
"You want sports to be a contest between the best of each category and the moment you blur the boundary around women's sport, you no longer allow that to happen."
Dr Tucker said the "jury is still out" on whether or not people who transition before puberty have an advantage.
"There is evidence at the moment that, once you go through puberty under the influence of male hormones like testosterone, you can't undo that advantage," he said.
"There is, as yet, no strong evidence for what happens to male biology and hence performance advantage if puberty is suppressed.
"I've seen recent evidence showing that even before puberty, male advantage exists because it's created from the moment of conception, but until evidence exists not many sports will draw the line before that."
Dr Tucker rejected the idea that transgender athletes are being "excluded" from sports they love.
"They're excluded from the category that they're not born into," he said.
"If you don't regulate it, then let's let all humans compete in one category because you effectively undermine the integrity of women's sports.
"We want, obviously, to let people live the life they wish to live and identify in the gender in which they wish to identify, but that does not automatically guarantee or give that person the right to participate in a category that they don't belong in."
Last year, the IRFU banned transgender women from playing against other adult women in contact rugby in Ireland.
Trans Equality Together Co-Director Moninne Griffith condemned the decision, saying it "directly affects a very small number of trans players in Ireland, but it will have deep-reaching negative consequences across society".
"It is openly sending a message to trans people, their families and allies that they are not welcome in the rugby community," she said.
"We note the IRFU's values include respect, integrity, and inclusivity - this decision flies in the face of these values."