Description

We present a fair and safe method for determining eligibility for the female sports category so that female athletes can be protected from competing against males. This video is inspired by an editorial called “Fair and Safe Eligibility Criteria for Women’s Sport” by Tucker, Hilton, & McGawley et al.

This editorial was published as a result of the 2024 Paris Olympics controversy over female category eligibility, where two male athletes competed in the female boxing category.

Collaborators

• Gregory Brown, Department of Kinesiology and Sport Sciences, University of Nebraska at Kearney

• Emma Hilton, School of Biological Sciences, University of Manchester

• Jonathan Pike, Department of Philosophy, Faculty of Arts and Social Sciences, The Open University

• Ross Tucker, Department of Sport Science, Institute of Sport and Exercise Medicine, University of Stellenbosch

Transcript

The female sports category exists to ensure safe and fair competition for female athletes, since males have significant performance advantages compared to females of equal height, weight, and age. These male advantages include larger skeletal structures, greater muscle mass with stronger muscles capable of producing force more rapidly, stronger tendons and ligaments, larger hearts and lungs, and a higher oxygen-carrying capacity (Pike, Hilton, & Howe, 2021). These advantages arise from a combination of testes, high testosterone production, and a functional androgen receptor response that drives physical changes in the male’s body throughout childhood and puberty, a process called androgenization (Handelsman, 2017; Catley & Tomkinson, 2013; Handelsman, Hirschberg, & Bermon 2018; Eiberg et al., 2005; Brown et al. 2025; Emeljanovas et al., 2020; Tambalis et al., 2016; Tomkinson et al., 2017, 2018). Even if testosterone is suppressed, the physiological advantages caused by androgenization remain (Hilton & Lundberg 2021).

To protect females and the integrity of the female sports category, athletes wishing to enter this category should be screened for eligibility, and those athletes who may have benefitted from male development excluded pending further investigation. Screening should occur at initial registration for entering the female category to prevent media scrutiny later and to ensure timely medical evaluation if needed.

But how do we employ a screen that is not only highly predictive of male development, but also simple, fast, and non-invasive?

Consider the cheek swab. A cotton swab is gently rubbed against the inner cheek, coating the cotton in saliva and collecting hundreds of thousands of buccal cells. DNA strands are then extracted from these cells. Then, a specific DNA sequence from the strand is amplified, creating millions of copies of it to detect a target gene. This is known as Polymerase Chain Reaction, or PCR (National Human Genome Research Institute, 2020). In this case, technicians use PCR to confirm the presence or absence of the SRY gene in the extracted DNA. SRY is responsible for initiating the development of testes and is known as the master switch for male development (Sekido & Lovell-Badge, 2009; Kashimada & Koopman, 2010; Kimball, 2020). PCR analysis for SRY is used in research worldwide where the sex of a mammal must be identified (Ardıclı, Bozkurt, & Vatansever, 2023; Hrovatin & Kunej, 2017; Luptakova et al., 2011). It is also cheap, comparable in price to testing for the sex of a baby or a genetic condition. Most importantly, it is highly predictive of male development, accurately classifying over 99.99% of individuals as either male or female (Richardson, Scott, & McLennan, 2017; O’Connell, Atlas, Ayers, & Sinclair, 2023; Sax 2002).

But what about the remaining cases? Rare developmental disorders may cause discrepancies between the screen result and an individual’s actual development. When such cases are flagged by the screen, a structured review process is initiated: first, the athlete is referred to independent medical specialists for diagnosis of a potential medical condition. Second, their female category application is temporarily suspended while the medical evaluation takes place. Third, if the evaluation confirms no testosterone-driven male development, the athlete may resubmit their application for consideration. However, if the athlete is found to have experienced male development, they will remain ineligible for women’s sports. This approach leaves complex decisions to medical experts, ensures ethical safeguards, and sets a clear protocol for handling atypical results.

Let’s look at three examples of atypical cases: Swyer Syndrome, CAIS, and 5-ARD.

1.       46:XY Swyer Syndrome (occurring in 1 in 80,000 births)

• Individuals can sometimes be SRY positive, but a mutation in downstream male-sex determining genes results in failure of the gonads to differentiate, leaving underdeveloped clumps of tissue called streak gonads.

• With no testes to produce male levels of anti-Mullerian hormone, they develop female internal genitalia. Finally, without male levels of testosterone, and thus, little to no DHT, they develop female external genitalia.

• Since they never experience testosterone-driven male development, they do not have the male performance advantage associated with androgenization.

2.       46:XY Complete Androgen Insensitivity Syndrome (CAIS) (occurring in 1 in 50,000 to 1 in 20,000 births)

• Individuals are SRY positive, and have testes that produce testosterone, but a mutation in the androgen receptor gene blocks their body’s ability to respond to testosterone.

• With no testosterone or DHT reception, they develop female-typical external anatomy and never undergo male physiological development. Their body still receives the anti-Mullerian hormone produced from the testes, however, and so they do not develop the Mullerian ducts.

• Like cases of Swyer Syndrome, since individuals with CAIS never experience testosterone-driven male development, they do not have the male performance advantage associated with androgenization.

3.       46:XY 5-Alpha Reductase Deficiency (5-ARD) (exact rates are unknown. It is very rare in the first world but more common in certain regions, such as the Dominican Republic or Turkey)

• Individuals are SRY positive and have functioning testes. These testes produce testosterone in the male range, forming the male’s internal genitalia. However, a mutation in the SRD5A2 gene causes a deficiency in the 5-alpha reductase type 2 enzyme. Without this enzyme, testosterone cannot be converted into its more potent form, dihydrotestosterone (DHT). With little to no DHT, the male’s external genitalia are underdeveloped or even female-like. They are therefore sometimes misidentified as females at birth.

• This deficiency in DHT, however, does not impact their male-level testosterone production or androgen receptor response to testosterone.

• Since they experience testosterone-driven male development, they do have the male performance advantage.

With no official sex screening in place since 1996, male athletes with XY 5-ARD have competed and won medals in women’s Olympic events due to their testosterone-driven male development.

Thus, as we can see from these cases, the key distinction is whether an athlete has experienced testosterone-driven male development (as in the case of XY 5-ARD) or has not (as in the cases of Swyer Syndrome and CAIS). This differentiation is crucial for maintaining the fairness of female competition.

The combination of the SRY cheek swab and medical assessment for atypical results provides a precise and ethical method for identifying and then evaluating potential disorders and male advantages. This process creates an important distinction between screening—an initial step to detect the SRY gene—and diagnosis, which involves a more thorough medical evaluation. Eligibility should not be determined solely by the screen results; rather, the SRY cheek swab serves as a cost-effective, rapid first step to identify athletes who may need further review. This approach ensures the integrity of female competition and a fair, ethical process for all athletes.

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