From September 2025, every athlete who wishes to compete in the female category at world ranking athletics competitions will have to undergo a once-in-a-lifetime test for the SRY gene. World Athletics has framed this as a move towards transparency, fairness, and consistency; however, the decision raises profound questions about how science, identity, and human rights are intertwined in sport. To understand what is at stake, one must first examine how the female category is defined under the new rules.
The female category under Rule 3.5
The female category is not left open to self-declaration. It is explicitly defined in World Athletics’ Eligibility Rule 3.5. According to this rule, participation is reserved primarily for biological females. Biological females who have taken testosterone as part of male gender-affirming treatment cannot return to women’s competition until at least four years after their last use, with the precise period determined on a case-by-case basis. There are also provisions for some individuals born male: those with Complete Androgen Insensitivity Syndrome, who, despite having XY chromosomes, do not undergo male sexual development or puberty, remain eligible. In addition, a narrow group of athletes with differences of sex development (DSD) may continue under transitional provisions if they meet strict hormonal conditions. The female category, therefore, is being defined not merely in social or identity terms but in deeply genetic and biological language.
What exactly is the SRY gene?
The SRY gene, short for Sex-determining Region Y, lies on the Y chromosome. It functions as the switch that initiates the male developmental pathway in embryos, directing the gonads to form testes and triggering testosterone production. Without SRY, the default pathway is ovarian development, leading to female differentiation. This central role is why World Athletics has chosen it as a gatekeeper marker. If the SRY gene is absent, the individual is presumed to have followed the female developmental pathway and is admitted into the female category. If it is present, further review is triggered to determine eligibility.
Yet biology is rarely so binary. Some individuals with XY chromosomes carry mutations that render the SRY gene inactive and thus develop as females. Others may have the gene translocated onto an X chromosome, resulting in an XX male. Beyond SRY, a cascade of genes, including SOX9, RSPO1, and WNT4, modulate sex development. The presence of SRY is therefore powerful but not absolute.
Why test for SRY and not chromosomes or hormones?
In earlier decades, sex verification in sport relied on chromosomal checks such as Barr body testing or full karyotyping. These methods caused repeated misclassification of women with intersex variations, leading to their abandonment in the 1990s. More recently, World Athletics used circulating testosterone levels to determine eligibility, setting cut-offs at 10 nmol/L and later 5 nmol/L. But hormone levels fluctuate, require constant monitoring, and were repeatedly challenged in court, with critics arguing that the link between testosterone and athletic performance was unproven and discriminatory.
SRY testing offers something different: a single genetic result, unchanging across life, that can be measured quickly and cheaply from a cheek swab. Once tested, an athlete never needs to repeat the procedure. For administrators, this is efficient. For athletes, it avoids repeated invasive testing. It is, on the surface, a clear dividing line.
The promise of clarity and consistency
Proponents of the new policy argue that the SRY test establishes a consistent, scientifically grounded criterion. World Athletics stresses that the test is highly accurate, using quantitative fluorescent PCR technology with minimal risk of error. Privacy safeguards are in place: results remain with the athlete unless they choose to share them with their doctor or the governing body’s medical manager. The process, according to the FAQs, was shaped through consultations with stakeholders, many of whom favored a genetic test over hormone monitoring.
The advantages are not trivial. Athletes no longer have to submit to repeated hormone testing. The once-in-a-lifetime model is less intrusive and, at least in theory, avoids the perception of arbitrariness. It also sidesteps the legal controversies that surrounded testosterone thresholds, providing regulators with a firmer ground to enforce boundaries in women’s sport.
The criticisms
Yet the very simplicity that makes the SRY test attractive to administrators is also its greatest weakness. Critics point out that human sex development cannot be reduced to a single gene. An athlete with Complete Androgen Insensitivity Syndrome will test positive for SRY, yet her body cannot respond to testosterone, and she develops and lives as female. Such women are explicitly exempted under Rule 3.5, but many other DSD conditions are not. For them, a positive SRY test may spell exclusion, even if they have always competed as women and identified as such.
There are also ethical concerns. Mandatory genetic testing without the possibility of refusal, since refusal leads to disqualification from world ranking competitions, raises issues of consent and dignity. Athletes may discover for the first time through this test that they carry a DSD, a revelation with far-reaching medical and psychological implications. Without adequate support, the test risks being not just an eligibility filter but a source of trauma.
Another criticism lies in the optics of fairness. By centering on SRY, the policy risks reviving the discredited “sex verification” models of the past. Instead of acknowledging the spectrum of biology, it reinforces a binary that many scientists argue is simplistic. The result could be the unjust exclusion of women whose only “fault” is that their genes do not fit an administrative category.
Transitional measures and contested ground
World Athletics has acknowledged that some athletes are caught midstream by the rule change. A very small number of DSD athletes already competing under the 2023 regulations will be allowed to continue for the remainder of their careers, provided they keep testosterone levels below 2.5 nmol/L. No such provisions exist for transgender athletes, who remain excluded if they have undergone male puberty. For many, this unequal treatment underscores that the new policy is less about scientific consistency and more about managing political pressures.
The role of genetic counselling
Perhaps the most important element missing in the policy rollout is recognition of the need for genetic counselling. For an athlete, being told they are SRY-positive is not just a matter of eligibility; it is a revelation about their own biology. It may imply differences in reproductive anatomy, fertility, hormone production, and even long-term health risks. Counselling is crucial to help athletes interpret these results, process their emotions, and make informed choices. Without it, the policy risks reducing people to laboratory reports rather than respecting them as whole human beings.
Science, fairness, and humanity
The SRY gene test is an attempt to resolve one of sport’s most contentious debates: how to define female eligibility in a world where biology and identity do not always align neatly. It promises clarity but risks exclusion. It offers efficiency but may sacrifice nuance. It is justified as a matter of fairness, yet it may undermine the very inclusivity it seeks to protect.
What is clear is that science alone cannot settle these debates. Fairness in sport must be weighed alongside dignity, privacy, and human rights. The new regulations may create more stability for governing bodies, but they will also reshape the lives of athletes who find themselves on the wrong side of a gene.
As genetics becomes part of the sporting rulebook, society faces a deeper question: do we want sport to reflect the complexities of human biology, or do we want to enforce neat categories even at the cost of fairness to individuals? The answer will define not just who gets to compete, but what sport itself stands for.
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